10 Channel LED Backlight Driver with Integrated Power Supply 34844 34844A

10 Channel LED Backlight Driver with Integrated Power Supply 34844 34844A
Freescale Semiconductor
Advance Information
Document Number: MC34844
Rev. 9.0, 3/2012
10 Channel LED Backlight Driver
with Integrated Power Supply
The 34844/A is a high efficiency, LED driver for use in backlighting
LCD displays from 10" to 20"+. Operating from supplies of 7.0 to 28 V,
the MC34844/A is capable of driving up to 160 LEDs in 10 parallel
strings. Current in the 10 strings is matched to within ±2%, and can be
programmed via the I2C/SM Bus interface.
The 34844/A also includes a Pulse Width Monitor (PWM) generator
for LED dimming. The LEDs can be dimmed to one of 256 levels,
programmed through the I2C/SM Bus interface. Up to 65,000:1 (256:1
PWM, 256:1 Current DAC) dimming ratio.
The integrated boost converter generates the minimum output
voltage required to keep all LEDs illuminated with the selected current,
providing the highest efficiency possible.
The 34844 has an integrated boost self-clocks at a default
frequency of 600 kHz, but may be programmed via I2C to 150/300/
600/1200 kHz. The PWM frequency can be set from 100 Hz to 25 kHz,
or can be synchronized to an external input. If not synchronized to
another source, the internal PWM rate outputs on the CK pin. This
enables multiple devices to be synchronized together.
The 34844A has a default boost frequency of 320 kHz, but may be
programmed via I2C to 160/320/650/1300 kHz. The PWM frequency
can be set from 110 Hz to 27 kHz, or can be synchronized to an
external input. If not synchronized to another source, the internal PWM
rate outputs on the CK pin. This enables multiple devices to be
synchronized together.
The 34844/A also supports optical/temperature closed loop
operation and also features LED over-temperature protection, LED
short protection, and LED open circuit protection. The IC also includes
over-voltage protection, over-current protection, and under-voltage
lockout.
34844
34844A
LED DRIVER
EP SUFFIX (PB-FREE)
98ASA10800D
32-PIN QFN-EP
ORDERING INFORMATION
Device
MC34844EP/R2
MC34844AEP/R2
Temperature
Range (TA)
Package
-40 °C to 105 °C
32 QFN-EP
Features
• Input voltage of 7.0 to 28 V
• 2.5 A integrated boost FET
• Up to 50 mA on the 34844 LED current per channel
• Up to 80 mA on the 34844A LED current per channel
• 90% efficiency (DC:DC)
• I2C/SM Bus interface
• 10 channel current mirror with ±2% current matching
• Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)
• PWM frequency programmable or synchronizable from 100 to 25,000 Hz for the 34844
• PWM frequency programmable or synchronizable from 110 to 27,000 Hz for the 34844A
• 32-Ld 5x5x1.0mm TQFN Package
Applications
•
•
•
•
Monitors and HDTV - up to 42 inch
Personal Computer Notebooks
GPS Screens
Small screen Televisions
* This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© Freescale Semiconductor, Inc., 2009-2012. All rights reserved.
34844
VIN
VDC1
VDC2
7.0 to 28 V
SWA
SWB
VOUT
VDC3
PGNDA
COMP
PGNDB
SLOPE
Control Unit
VDC1
VDC1
FAIL
SCK
SDA
A0/SEN
CK
ISET
PIN
NIN
~
~
~
~
~
~
~
~
~
~
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
PWM
M/~S
EN
VDC1
VCC
GND
Figure 1. MC34844 Simplified Application Diagram (SM Bus Mode)
34844A
VIN
7.0 to 28V
SWA
SWB
VDC1
VDC2
PWM
PGNDA
COMP
PGNDB
SLOPE
Control Unit
FAIL
SCK
SDA
PWM
PWM
VOUT
VDC1
A0/SEN
CK
M/~S
EN
VDC1
ISET
PIN
NIN
VOUT
VOUT
VDC3
GND
VCC
~
~
~
~
~
~
~
~
~
~
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
Figure 2. MC34844A Simplified Application Diagram (Manual Mode)
34844
2
Analog Integrated Circuit Device Data
Freescale Semiconductor
DEVICE VARIATIONS
DEVICE VARIATIONS
MC34844 is within the MC34844 Specifications Pages 4 to 31, MC34844A is within the MC34844A Specifications Pages 32
to 54
Table 1. Key Device Variations between the MC34844 and MC34844A
Electrical Parameter(1)
Condition
Value
Maximum LED Current
mA
34844
55
34844A
85
LED Channel Sink Current
(typ)
34844
RISET=5.1 kΩ ±0.1%
50
34844A
RISET=3.48 kΩ ±0.1%
80
Switching Frequency
34844
34844A
PWM Frequency Range
34844
Unit
(typ)
(BST [1:0]=0)
0.15
(BST [1:0]=1)
0.30
(BST [1:0]=2) [default]
0.60
(BST [1:0]=3)
1.20
(BST [1:0]=0)
0.16
(BST [1:0]=1)) [default]
0.32
(BST [1:0]=2)
0.65
(BST [1:0]=3)
1.30
This frequency range applies for Master
mode, Slave mode, and Manual mode
34844A
mA
MHz
Hz
100 - 25000
110 - 27000
Notes
1. Refer to the respective Electrical Parameters for specific details
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
3
MC34844
MC34844 SPECIFICATIONS PAGES 4 TO 31
MC34844 SPECIFICATIONS
PAGES 4 TO 31
34844
4
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
SWA
VIN
VDC1
VDC2
SWB
LDO
A0/SEN
OVP
VDC3
PGNDA
COMP
SLOPE
BOOST
CONTROLLER
PGNDB
VOUT
CK
EN
CLOCK/PLL
V SENSE
FAIL
M/~S
PWM
I0
PWM GENERATOR
I1
I2
SCK
SDA
I2C INTERFACE
10 CHANNEL
50 mA CURRENT
MIRROR
I3
I4
I5
I6
I7
I8
ISET
CURRENT DAC
PIN
TEMP/OPTO
LOOP CONTROL
NIN
I9
OCP/OTP/UVLO
GND
Figure 3. 34844 Simplified Internal Block Diagram
34844
5
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
PIN CONNECTIONS
VOUT
VDC2
M/~S
COMP
VDC1
SCK
SDA
PWM
PIN CONNECTIONS
32
31
30
29
28
27
26
25
VIN 1
24 CK
PGNDB 2
23 VDC3
TRANSPARENT
TOP VIEW
SWB 3
SWA 4
22 SLOPE
21 NIN
QFN - EP
5.0 MM X 5.0 MM
32 LEAD
PGNDA 5
20 PIN
EP GND
A0/SEN 6
19 ISET
EN 7
18 FAIL
IO 8
EP = Exposed Pad
17 I9
9
10
11
12
13
14
15
16
I1
I2
I3
I4
I5
I6
I7
I8
Figure 4. 34844 Pin Connections
Table 2. 34844 Pin Definitions
A functional description of each pin can be found in the Functional Pin Description section beginning on page 14.
Pin Number
Pin Name
Pin Function
Formal Name
Definition
1
VIN
Power
Input voltage
2
PGNDB
Power
Power Ground
Power ground
3
SWB
Input
Switch node B
Boost switch connection B
4
SWA
Input
Switch node A
Boost switch connection A
5
PGNDA
Power
Power Ground
Power ground
6
A0/SEN
Input
Device Select
Address select, device select pin or OVP HW control
7
EN
Input
Enable
8 - 17
I0-I9
Input
LED Channel
18
FAIL
Open Drain
Fault detection
19
ISET
Passive
Current set
20
PIN
Input
Positive current scale
21
NIN
Input
Negative current scale Negative input analog current control
22
SLOPE
Passive
Boost Slope
23
VDC3
Output
Internal Regulator 3
24
CK
Input/Output
Clock signal
Input supply
Enable pin (active high, internal pull-up)
LED string connections
Fault detected pin (open drain):
No Failure = Low-impedance
Failure = High-impedance
LED current setting resistor
Positive input analog current control
Boost slope compensation Setting resistor
Decoupling capacitor for internal phase locked loop power
Clock synchronization pin (input for M/~S = low - internal pull-up, output
for M/~S = high)
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
6
MC34844
PIN CONNECTIONS
Table 2. 34844 Pin Definitions (continued)
A functional description of each pin can be found in the Functional Pin Description section beginning on page 14.
Pin Number
Pin Name
Pin Function
Formal Name
Definition
25
PWM
Input
External PWM
26
SDA
Bidirectional
I2C data
I2C data Line
27
SCK
Bidirectional
I2C clock
I2C clock line
28
VDC1
Output
Internal Regulator 1
29
COMP
Passive
Compensation pin
30
M/~S
Input
Master/Slave selector
Selects Master mode (1) or Slave mode (0)
31
VDC2
Output
Internal Regulator 2
Decoupling capacitor for internal regulator
32
VOUT
Input
Voltage Output
EP
GND
-
Ground
External PWM input (internal pull-down)
Decoupling capacitor for internal logic rail
Boost converter Type compensation pin
Boost Output voltage sense pin
Ground Reference for all internal circuits other than Boost FET
34844
7
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 3. Maximum Ratings
All voltages are with respect to ground, unless otherwise noted. Exceeding these ratings may cause a malfunction or
permanent damage to the device.
Ratings
Symbol
Value
Unit
ELECTRICAL RATINGS
Maximum Pin Voltages
VMAX
V
A0/SEN
7.0
I0, I1, I2, I3, I4, I5, I6, I7, I8, I9,EN(5)
45
VIN
30
SWA, SWB, VOUT
65
FAIL, PIN, NIN, ISET, M/~S, CK, PWM
6.0
Maximum LED Current
ESD
IMAX
Voltage(2)
55
VESD
mA
V
Human Body Model (HBM)
+2000
Machine Model (MM)
+200
THERMAL RATINGS
Ambient Temperature Range
Junction to Ambient Temperature
Junction to Case Temperature
(3)
(3)
Maximum junction temperature
Storage temperature range
Peak Package Reflow Temperature During Reflow
(4)
TA
-40 to 105
°C
TθJA
32
°C/W
TθJC
3.5
°C/W
TJ
150
°C
TSTO
-40 to 150
°C
TPPRT
260
°C
Power Dissipation
W
TA = 25 °C
3.9
TA = 70 °C
2.5
TA = 85 °C
2.0
TA = 105 °C
1.4
Notes
2. ESD testing is performed in accordance with the Human Body Model (HBM) (AEC-Q100-2), and the Machine Model (MM) (AEC-Q100003), RZAP = 0 Ω
3.
4.
5.
Per JEDEC51 Standard for Multilayer PCB
Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may
cause malfunction or permanent damage to the device.
45 V is the Maximum allowable voltage on all LED channels in off-state.
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
8
MC34844
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Static and Dynamic Electrical Characteristics
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1,
PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
VIN
7.0
12
28
V
Manual & SM Bus: EN = Low, SCK & SDA=Low
-
2.0
-
μA
I2C: EN = Low, SETI2C bit = 1, CLRI2C bit = 0
-
17
-
ISLEEP
-
3.0
-
mA
IOPERATIONAL
-
10.0
-
mA
UVLO
5.4
6.0
6.4
V
UVLOHYST
150
200
250
mV
VDC1
2.4
2.5
2.6
V
VDC2
5.5
6.0
6.5
V
VDC3
2.4
2.5
2.6
V
SUPPLY
Supply Voltage
Supply Current when Shutdown Mode
Supply Current when Sleep Mode
ISHUTDOWN
SM-Bus: EN = low, SCK & SDA= Active, SETI2C bit = 0, EN bit = 0
I2C: EN = High, SETI2C bit = 1, CLRI2C bit = 0, EN bit = 0
Supply Current when Operational Mode
Manual: EN= High, SCK & SDA=Low, PWM=Low
SM-Bus: EN= Low, SCK & SDA=Active, EN bit= 1, PWM=Low
I2C: EN = High, SETI2C bit = 1, CLRI2C bit = 0, EN bit = 1, PWM=Low
Under-voltage Lockout
VIN Rising
Under-voltage Hysteresis
VIN Falling
VDC1 Voltage(6)
CVDC1 = 2.2 μF
VDC2 Voltage(6)
CVDC2 = 2.2 μF
VDC3 Voltage(6)
CVDC3 = 2.2 μF
BOOST
Output Voltage Range(7)
V
VIN = 7.0 V
VOUT1
8.0
-
43
VIN = 28 V
VOUT2
31
-
60
IFET
2.3
2.5
2.7
A
RDSON
-
250
500
mΩ
IBOOST_LEAK
-
-
10
μA
EFFBOOST
-
90
-
%
Boost Switch Current Limit
RDSON of Internal FET
IDRAIN= 1.0 A
Boost Switch Off-state Leakage Current
VSWA,SWB = 65 V
Peak Boost Efficiency(8)
Notes
6. This output is for internal use only and not to be used for other purposes. A 1.0 kΩ resistor between the VDC3 and VDC1 pin is
recommended for <-20 °C operation.
7. Minimum and Maximum output voltages are dependent on Min/Max duty cycle condition.
8. Guaranteed by design
34844
9
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1,
PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
IOUT/VIN
-0.2
-
0.2
%/V
IOUT/VLED
-0.2
-
0.2
%/V
VSLOPE
-
0.49
-
V/μs
ACSA
-
9.0
-
Current Sense Resistor
RSENSE
-
22
-
mΩ
OTA Transconductance
GM
-
200
-
μS
Transconductance Sink and Source Current Capability
ISS
-
100
-
μA
VHOLD
0.45
0.5
0.55
V
IFAIL_LEAK
-
-
5
μA
VOL
-
-
0.4
V
ISINK
49
50
51
mA
VMIN
675
750
825
mV
IMATCH
-2.0
-
2.0
%
VSET
2.017
2.048
2.079
V
ILEDRES
-
1.5
-
%
ICH_LEAK
-
-
10
μA
VPIN_DIS
2.2
-
-
V
IPIN
-2.0
-
2.0
μA
Line Regulation (9)
VIN=7.0 to 28 V
Load Regulation (9)
VLED = 8.0 to 65 V (all Channels)
Slope compensation voltage ramp
RSLOPE = 68 kΩ
Current Sense Amplifier Gain
Output Voltage Precharge
FAIL PIN
Off-state Leakage Current
VFAIL = 5.5 V
On-state Voltage Drop
ISINK = 4.0 mA
LED CHANNELS
Sink Current
ICHx Register = 255, RISET=5.1 kΩ 0.1%, PIN&NIN = Disabled,
TA=25 °C
Regulated minimum voltage across drivers
Pulse Width > 4.0 μs
Current Matching Accuracy
ISET Pin Voltage
RISET=5.1 kΩ 0.1%
LED Current Amplitude Resolution
1.0 mA < ILED < 50 mA
Off-state Leakage Current, All channels
(VCH = 45 V)
PIN INPUT
Voltage to Disable PIN mode
PIN Bias Current
PIN = VSET
Analog Dimming Current
IDIM_PIN
mA
ICHx Register = 255, RISET=5.1 kΩ 0.1%
PIN = VSET/2
23.75
25
26.25
PIN = VSET
47.50
50
52.50
Notes
9. Guaranteed by design
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
10
MC34844
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1,
PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
VNIN_DIS
2.2
-
-
V
ININ
-2.0
-
2.0
μA
NIN INPUT
Voltage to Disable NIN mode
NIN Bias Current
NIN = VSET
Analog Dimming Current
IDIM_NIN
mA
ICHx Register = 255, RISET=5.1 kΩ 0.1%
NIN = VSET/2
23.75
25
26.25
NIN = 0 V
47.50
50
52.50
150
165
175
-
25
-
OVER-TEMPERATURE PROTECTION
Over-temperature Threshold(10)
OTT
Rising
Hysteresis
°C
2
I C/SM BUS PHYSICAL LAYER [SCK, SDA]
I2C Address
ADRI2C
-
1110110
-
Binary
SM-Bus Address
ADRSMB
-
1110110
-
Binary
Input Low Voltage
VILI
-0.3
-
0.8
V
Input High Voltage
VIHI
2.1
-
5.5
V
Input Hysteresis
VHYSI
0.3
-
-
V
Output Low Voltage
VOLI
-
-
0.4
V
IINI
-5.0
-
5.0
μA
CINI
-
-
10
ρF
Input Low Voltage
VILL
-0.3
-
0.5
V
Input High Voltage
VIHL
1.5
-
5.5
V
VHYSL
-
0.1
-
V
IIIL
-5.0
-
5.0
μA
VOLL
-
-
0.2
V
VOHL
2.2
-
5.5
V
CINI
-
-
5.0
ρF
Sink Current < 4.0 mA
Input Current
Input
Capacitance(10)
LOGIC INPUTS / OUTPUTS (CK, M/~S, PWM, A0/SEN)
Input Hysteresis
Input Current
Output Low Voltage (CK)
ISINK < 2.0 mA
Output High Voltage (CK)
ISOURCE < 2.0 mA
Input Capacitance(10)
Notes
10. Guaranteed by design
34844
11
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1,
PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
OVP = Fh
OVPFH
60.5
62.5
64.5
V
OVP = Eh
OVPEH
56.5
58
60
V
OVP = Dh
OVPDH
53
54
56
V
OVP = Ch
OVPCH
49
51
52.5
V
OVP = Bh
OVPBH
45
47
48.5
V
OVP = Ah
OVPAH
41
43
44.5
V
OVP = 9h
OVP9H
38
39
40.5
V
OVP = 8h
OVP8H
34
36
37.5
V
OVP = 7h
OVP7H
30.5
32
33.5
V
OVP = 6h
OVP6H
26
28
30
V
OVP = 5h
OVP5H
23
24
25
V
OVP = 4h
OVP4H
19
20
21
V
OVP = 3h
OVP3H
15
16
17
V
OVP = 2h
OVP2H
11
12
13
V
Over-voltage threshold,
OVPHW
6.15
6.5
6.85
V
ISINK_OVP
-
100
-
μA
Switching Frequency (BST [1:0]=0)
fSW0
0.14
0.15
0.17
MHz
Switching Frequency (BST [1:0]=1)
fSW1
0.27
0.30
0.33
MHz
Switching Frequency (BST [1:0]=2)
fSW2
0.54
0.60
0.66
MHz
Switching Frequency (BST [1:0]=3)
fSW3
1.08
1.2
1.32
MHz
Minimum Duty Cycle
DMIN
-
10
15
%
Maximum Duty Cycle
OVER-VOLTAGE PROTECTION
Over-voltage Clamp - OVP Register Table:
Set by Hardware, Voltage at A0/SEN
A0/SEN Sink Current
BOOST
DMAX
80
85
-
%
Soft Start Period
tSS
-
6.5
-
ms
Boost Switch Rise Time(10)
tTR
-
15
-
ns
Boost Switch Fall Time(10)
tF
-
25
-
ns
Notes
11. Guaranteed by design
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
12
MC34844
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, ILED = 50 mA, PWM = VDC1, M/~S = VDC1,
PIN & NIN = VDC1, - 40 °C ≤ TA ≤ 105 °C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
fPWMS
100
-
25000
Hz
PWM GENERATOR
PWM Frequency Range (13)
M/~S = Low (Slave Mode)
PWM Frequency
fPWMM
Hz
M/~S = High (Master Mode)
FPWM Register = 768
22500
25000
27500
90
100
110
tfPWM
-
0.39
-
%
tPWM_IN
150
-
-
ns
fPWM
100
-
23000
Hz
fCKS
100
-
25000
Hz
fCKS_JITTER
-
-
0.1
%
FPWMS=25 kHz
-
-
50
ms
FPWMS=100 Hz
-
2000
-
ms
22500
25000
27500
Hz
90
100
110
FPWM Register = 192,000
PWM dimming resolution
PWM PIN (DIRECT PWM CONTROL)
Input PWM Pin Minimum Pulse(13)
Input PWM Frequency Range
PHASE LOCK LOOP
CK Slave Mode Frequency Lock Range(12)
M/~S = Low (Slave Mode)
CK Slave Mode Input Jitter(13)
M/~S = Low (Slave Mode)
Slave Mode Acquisition Time
TS_ACQ
M/~S = Low (Slave Mode)
CK Frequency (Master Mode)
fCKMASTER
FPWM Register = 768
FPWM Register = 192,000
I2C/SM BUS PHYSICAL LAYER [SCK, SDA]
Interface Frequency Range
fSCK
SM Bus Power-on-Reset Time
tRST
-
tF
Output fall time
400
kHz
-
100
ms
40
-
160
ns
tR
20
-
80
ns
tR/tF
-
-
25
ns
tR/tF
-
23
50
ns
10 ρF < CL < 400 ρF
Output rise time
10 ρF<CL<400 ρF
LOGIC OUTPUT (CK)
Output Rise and Fall time(12)
CL<100 ρF
LED CHANNELS
Channels Rise and Fall Time(13)
Notes
12. Special considerations should be made for frequencies between 100 Hz to 1.0 KHz. Please refer to Functional Device Operation for
further details.
13. Guaranteed by design
34844
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Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
LED backlighting has become very popular for small and
medium LCDs, due to some advantages over other
backlighting schemes, such as the widely used cold cathode
fluorescent lamp (CCFL). The advantages of LED
backlighting are low cost, long life, immunity to vibration, low
operational voltage, and precise control over its intensity.
However, there is an important drawback of this method. It
requires more power than most of the other methods, and this
is a major problem if the LCD size is large enough.
To address the power consumption problem, solid state
optoelectronics technologies are evolving to create brighter
LEDs with lower power consumption. These new
technologies together with highly efficient power
management LED drivers are turning LEDs, a more suitable
solution for backlighting almost any size of LCD panel, with
really conservative power consumption.
One of the most common schemes for backlighting with
LED is the one known as “Array backlighting”. This creates a
matrix of LEDs all over the LCD surface, using defraction and
diffused layers to produce an homogenous and even light at
the LCD surface. Each row or column is formed by a number
of LEDs in series, forcing a single current to flow through all
LEDs in each string.
Using a current control driver, per row or column, helps the
system to maintain a constant current flowing through each
line, keeping a steady amount of light even with the presence
of line or load variations. They can also be use as a light
intensity control by increasing or decreasing the amount of
current flowing through each LED string.
To achieve enough voltage to drive a number of LEDs in
series, a boost converter is implemented, to produce a higher
voltage from a smaller one, which is typically used by the
logical blocks to do their function.
The 34844 implements a single channel boost converter
together with 10 input channels, for driving up to 16 LEDs per
string to create a matrix of more than 160 LEDs. Together
with its 90% efficiency and I2C programmable or external
current control, among other features, makes the 34844 a
perfect solution for backlighting small and medium size LCD
panels, on low power portable and high definition devices.
FUNCTIONAL PIN DESCRIPTION
INPUT VOLTAGE SUPPLY (VIN)
IC ENABLE (EN)
IC Power input supply voltage, is used internally to
produce internal voltage regulation (VDC1, VDC3) for logic
functioning, and also as an input voltage for the boost
regulator.
The active high enable pin is internally pulled high through
pull-up resistors. Applying 0 V to this pin would stop the IC
from working.
INTERNAL VOLTAGE REGULATOR 1 (VDC1)
This pin is for internal use only, and not to be used for other
purposes. A capacitor of 2.2 μF should be connected
between this pin and ground for decoupling purposes.
INTERNAL VOLTAGE REGULATOR 2 (VDC2)
INPUT/OUTPUT CLOCK SIGNAL (CK)
This pin can be used as an output clock signal (master
mode), or input clock signal (slave mode), to synchronize
more than one device.
MASTER/SLAVE MODE SELECTION (M/~S)
This pin is for internal use only, and not to be used for other
purposes. A capacitor of 2.2 μF should be connected
between this pin and ground for decoupling purposes.
Setting this pin High puts the device into Master mode,
producing an output synchronization clock at the CK pin.
Setting this pin low, puts the device in Slave mode, using the
CK pin as an input clock.
INTERNAL VOLTAGE REGULATOR 3 (VDC3)
EXTERNAL PWM INPUT (PWM)
This pin is for internal use only, and not to be used for other
purposes. A capacitor of 2.2 μF should be connected
between this pin and ground for decoupling purposes. A
1.0 kΩ resistor between the VDC3 and VDC1 pin is
recommended for <-20 °C operation.
This pin is internally pulled down. An external PWM signal
can be applied to modulate the LED channel directly in
absence of an I2C interface.
BOOST COMPENSATION PIN (COMP)
Passive pin used to compensate the boost converter. Add
a capacitor and a resistor in series to GND to stabilize the
system.
CLOCK I2C SIGNAL (SCK)
Clock line for I2C communication.
ADDRESS I2C SIGNAL (SDA)
Address line for I2C communication.
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Freescale Semiconductor
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MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
A0/SEN
Address select, device select pin, or Hardware Overvoltage Protection (OVP) Control.
CURRENT SET (ISET)
Each LED string can drive up to 50 mA. The maximum
current can be set by using a resistor from this pin to GND.
POSITIVE CURRENT SCALING (PIN)
Positive current scaling factor for the external analog
current control. Applying 0 V to this pin, scales the current to
near 0%, and in the same way, applying 2.048 V (Vset), the
scale factor is 100%. By applying a voltage higher than 2.2 V,
the scaling factor is disabled, and the internal pull-ups are
activated.
If PIN pin and NIN pin are used at the same time then by
applying 0 V to the PIN pin and 2.048 V to NIN pin, scales the
current to near 0%, and in the same way, applying 2.048 V to
the PIN pin and 0 V to NIN pin, scales the current to 100%.
By applying a voltage higher than 2.2 V, the scaling factor is
disabled and the internal pull-ups are activated in both pins.
NEGATIVE CURRENT SCALING (NIN)
Negative current scaling factor for the external analog
current control. Setting 0 V to this pin scales the current to
100%, in the same way, setting 2.048 V (Vset) the scale
factor is near 0%. By applying a voltage higher than 2.2 V, the
scaling factor is disabled and the internal pull-ups are
activated.
If PIN pin and NIN pin are used at the same time then by
applying 0 V to the PIN pin and 2.048 V to NIN pin, scales the
current near 0%, and in the same way, applying 2.048 V to
the PIN pin and 0 V to NIN pin, scales the current to 100%.
By applying a voltage higher than 2.2 V, the scaling factor is
disabled and the internal pull-ups are activated in both pins.
GROUND (GND)
Ground Reference for all internal circuits other than the
Boost FET.
The Exposed Pad (EP) should be used for thermal heat
dissipation.
I0-I9
Current LED driver, each line has the capability of driving
up to 50 mA.
FAULT DETECTION PIN (FAIL)
When a fault situation is detected, this pin goes into high
impedance.
BOOST SLOPE COMPENSATION SETTING
RESISTOR (SLOPE)
Use an external resistor of about 68 kΩ to configure the
Boost compensation slope.
POWER GROUND PINS (PGNDA, PGNDB)
Ground pin for the internal Boost FET.
OUTPUT VOLTAGE SENSE PIN (VOUT)
Input pin to monitor the output voltage. It also supplies the
input voltage for the internal regulator 2 (VDC2).
SWITCHING NODE PINS (SWA, SWB)
Switching node of boost converter.
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Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34844 - Functional Block Diagram
Regulators / Power Down
Boost
3 Internal Regulators
Protection / Failure Detection
Over-temperature Protection
Over-current Protection
Under-voltage Protection
Over-voltage Protection
LED Open Protection
LED Channels
Logic Control
Optical and Temperature Control
PWM Dimming
Serial Interface Control
Regulator / Power down
Protection / Failure Detection
LED Channels
Logic Control
Boost
Figure 5. Functional Internal Block Diagram
REGULATORS/ POWER DOWN
The 34844 is designed to operate from input voltages in
the 7.0 to 28 V range. This is stepped down internally by
LDOs to 2.5 V (VDC1 and VDC3) and 6 V (VDC3) for
powering internal circuitry. If the input voltage falls below the
UVLO threshold, the device automatically enters in power
down mode.
Operating Modes:
The device can be operated by the EN pin and/or SDA/
SCK bus lines, resulting in three distinct operation modes:
• Manual mode, there is no I2C capability, the bus line pins
must be tied low, and the EN pin controls the ON/OFF
operation.
• SM Bus mode, EN pin must be tied low and the device is
turned ON by any activity on the bus lines. The part shuts
down if the bus lines are held low for more than 27 ms, the
27 ms watchdog timer can be disabled by I2C (setting
SETI2C bit high) or tying the EN pin high. In Sleep mode
(EN bit=0) the device reduces the power consumption by
leaving “alive” only the blocks required for I2C
communication.
• I2C mode, has to be configured by I2C communication
(SETI2C bit = 1) right after the IC is turned ON, it prevents
the part from being turned ON/OFF by the bus. Sleep
mode is also present and it is intended to save power, but
still keep the IC prepared to communicate by I2C. Turning
the EN pin OFF, the chip enters into a low power mode.
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Freescale Semiconductor
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MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Table 5. Operation Current Consumption Modes
Mode
Manual
SM Bus
EN Pin
SCK/SDA Pins
I2C Bit Command
Current Consumption
Mode
Low
Low
N/A
Shutdown
High
Low
N/A
Operational
Low
Low (> 27 ms)
EN bit = X
Shutdown
Low
Active
EN bit = 0
Sleep
Low
Active
EN bit = 1
Operational
Low
X
CLRI2C bit = 0
SETI2C bit = 1
I2C Low Power
(Shutdown)
Comments
Part Doesn’t
Wake-up
EN bit = X
SETI2C bit = 1
I2 C
High
X
CLRI2C bit = 0
Sleep
EN bit = 0
SETI2C bit = 1
High
X
CLRI2C bit = 0
Operational
EN bit = 1
BOOST
HARDWARE OVP:
The integrated boost converter operates in nonsynchronous mode and integrates a 2.5 A FET. An integrated
sense circuit is used to sense the voltage at the LED current
mirror inputs and automatically sets the boost output voltage
(DHC) to the minimum voltage needed to keep all LEDs
biased with the required current. The DHC is designed to
operate under specific pulse width conditions in the LED
drivers. It operates for pulse widths higher than 4.0 μs
If the pulse widths are shorter than specified, the DHC
circuit will not operate and the voltage across the LED drivers
will increase to a value given by the OVP minus the total LED
voltage in the LED string. Therefore it is imperative to select
the proper OVP level to minimize power dissipation.
The OVP can be set from 11 to 62 V, ~4.0 V spaced, using
the I2C interface (OVP Register). If I2C capability is not
present, the OVP can be controlled by a resistor divider
connected from VOUT to GND with its mid point tied to A0/
SEN pin (threshold = 6.5 V). During an OVP condition, the
output voltage will go to the OVP level which is programmed
via the I2C interface or settled by a resistor divider on A0/SEN
pin, or by a zener diode. The formulas to calculate the
hardware OVP using any of the two methods are as follows:
The OVP value should be set to greater than the maximum
LED voltage over the whole temperature range. A good
practice is to set it 5.0 V or so above the max LED voltage.
The boost converter also features internal Over-current
Protection (OCP) and has a user programmable Overvoltage Protection (OVP).
The OCP operates on a cycle by cycle basis. However, if
the OCP condition remains for more than 10 ms then the
device turns off the LED Drivers, the Boost goes to Sleep
mode and the output FAULT pin goes into high-impedance.
The device can only be restarted by recycling the enable or
creating a Power On Reset (POR).
The user can program the boost frequency by I2C
(BST[1:0]) only after the IC is powered up and before the
boost circuit is turned ON for the first time (PWM pin low to
high). This sequence avoids boost frequency to be changed
inadvertently during operation. The first I2C command has to
wait for 5.0 ms after the part is turned ON, in order to allow
sufficient time for the device power up sequence to be
completed.
The boost controller has an integral track and hold
amplifier with indefinite hold time capability, to enable
immediate LED on cycles after extended off times. During
extended off times, the external LEDs cool down from their
normal quiescent operating temperature and thereby
experience a forward voltage change, typically an increase in
the forward voltage. This change can be significant for
applications with a large number of series LEDs in a string
operating at high current. If the boost controller did not track
this increased change, the potential on the LED drivers would
saturate for a few cycles once the LED channels are reenabled.
Method 1
Method 2
VOUT
RUPPER
A0/SEN
RLOWER
VZENER2
A0/SEN
OVP = VZENER2 + 6.5 V
OVP = 6.5 V [(RUPPER / RLOWER) + 1] + (100E-6 x RUPPER)
34844
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Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Also the device has a precharge voltage that add 0.5 Volts
to the Boost, cycle by cycle of the PWM. It helps the boost to
respond faster every time the load turns back on again.
CURRENT MIRROR
The programmable current mirror matches the current in
10 LED strings to within 2%. The maximum current is set
using a resistor to GND from the ISET pin. This can be scaled
down using the I2C interface to 255 levels.
Zero current is achieved by turning off the LED Driver by
I2C (registers CHENx = 0 h) for a duty cycle from 0% to 99%
or by pulling PWM pin low regardless of the duty cycle.
I2C capability allows the channels to be controlled
individually or in parallel.
Current on LED Channel (PIN and NIN mode disabled)
Eqn. 1
ICH [ RegisterValue ]
Current [ A ] = ----------------------------------------------------------RSET [ ohms ]
In the off state, the LEDs current is set to 0 and the boost
converter stops switching.
This feature allows to drive more than 50 mA of current by
connecting the LED string to 2 or more LED channels in
parallel. For example; if the application requires to drive 5
channels at 100 mA, then the bottom of each LED string
should be connected to two channels in order to duplicate the
current capability (Example: CH0+CH1 = 100 mA).
PWM GENERATOR
The PWM generator can operate in either master or slave
modes, as set by the M/~S pin.
In master mode, the internal PWM generator frequency is
programmed through the I2C interface (registers FPWM).
The default programmed value set the number of 25 kHz
clocks (40 μs) in one PWM cycle. The 18-bit resolution allows
minimum PWM frequencies of 100 Hz to be programmed.
The resulting frequency is output on the CK pin.
PWM Frequency
Eqn. 2
19.2Mhz
PWMFrequency [ Hz ] = -------------------------------------------------------------------FPWM [ RegisterValue ]
In slave mode, the CK pin acts as an input. The internal
digital PLL uses this frequency as the PWM frequency. By
setting one device as master, and connecting the CK output
to the input on a number of slave configured devices, all
PWM frequencies are synchronized together.
The duty cycle of the PWM waveform in both master and
slave modes is set using a second register on the I2C
interface (register DPWM), and can be controlled from 100%
duty cycle to 1/256 TPWM = 0.39%. Zero percent of duty cycle
is achieved by turning LED drivers off (register CHENx = 0h)
or pulling PWM pin low.
An external PWM can also be used. The PWM input is
'AND'ed with the internal signal. By setting the serial interface
to 100% duty cycle (default), the external pin has full control
of the PWM duty cycle. This pin can also be used to modulate
the LED at a lower frequency than the PWM dimming
frequency (Minimum pulse width = 150 ns).
A pulsed mode can also be programmed using the I2C
interface (STROBE bit = 1). In this mode, each rising edge of
the PWM signal turns on the next channel, while turning off
all other channels. The duration that the channel is
illuminated is set by the duty cycle of the PWM input pin. This
can be used to scan the output channels.
DISABLING LED CHANNELS
The 34844 allows the user to enable and disable each of
the 10 channels separately by writing the corresponding
CHENx bit on Registers 08 and 09 thru I2C.
When a channel is disabled thru the I2C prior the device
starts to operate, the corresponding LED driver is disabled
but the feedback circuit is still connected. This may interfere
with the operation of the dynamic headroom control (DHC)
which can lead to erratic output voltage regulation. For this
condition, the output voltage may ramp up to the OVP level if
the voltage on the LED driver is not substantially above the
DHC regulation voltage (0.75 V typ). Because of this
operation under I2C/SMBUS Mode, we recommend to
connect the unused channels to VDC2 thru a100 kohm
resistor and also follow the below powering up sequence:
1. PWM pin = Low.
2. Power up the part.
3. Program the I2C commands and disable the unused
channels.
4. Enable the Boost and current drivers by taking PWM
pin to HIGH.
This previous device's operation does not happen when all
channels are being used because the voltage across the LED
drivers is always equal or higher than the DHC regulation
voltage (0.75 V typ). For this condition, the user can disable/
enable any of the channels thru I2C without causing any
erratic behavior but the FAIL pin cannot be cleared. If FAIL
pin is to be cleared thru I2C, it will be necessary to use the
suggested configuration shown at the FAIL PIN session.
FAIL PIN
If a LED fails open in any of the LED strings, the voltage in
that particular LED channel will be close to ground and the
LED open failure is detected. When this happens, a failure is
registered, the FAIL pin is set to its high-impedance stage,
and the channel is turned off.
The FAIL pin cannot be cleared for manual mode unless a
complete power on reset is applied. However for I2C/SMBUS
mode, the FAIL pin is cleared by disabling the malfunction
channels (CHENx = 0) and clearing the failure bit (CLRFAIL
bit = 1).
If the application only requires clearing the failure for the
floating or unused channels, then the unused channels must
be connected to VDC2 thru a 100 kohm resistor to avoid
reach instability problems. This will allow detecting another
failure from the connected channels. (See Figure 6)
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Freescale Semiconductor
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MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
If I2C communication is not present, FAIL condition should
be reset by removing the failure and re-enabling the device
thru the EN pin.
OPTICAL AND TEMPERATURE CONTROL LOOP
The 34844 supports both optical and temperature loop
control.
Figure 6. Single Channel Disconnect Circuit.
For applications where multiple failure detection is
required, then one 100 kohm resistor must be placed from
each channel to a diode (D2) connected to VDC2. The
resistor will provide a pull up voltage to the disconnected
channels so that they do not interfere with the DHC circuit.
The diode (D2) ensures that when the connected channels
are in PWM off state the LED strings do no conduct current
to VDC2. (See Figure 7)
For temperature loop control, the LED brightness can be
adjusted depending on the temperature of the LEDs.
For optical loop control, the 34844 supports both optical
closed loop backlight control, where the brightness of the
backlight is maintained at a required level by adjusting the
light output, until the desired level is achieved, or with
ambient light control, where the backlight brightness
increases as ambient light increases.
Both temperature and optical loops are supported through
the PIN and NIN pins. Each pin supports a 0-2.048 V input
range which affects the current through the LEDs. The PIN
pin increases current as the voltage rises from 0-2.048 V.
The NIN pin reduces current as the voltage rises from 02.048 V.
A 10.2 k resistor or higher value must be used at the ISET
pin if the part is configured to use PIN+NIN control loop
functionality, the 50 mA maximum current is achieved at the
higher allowed level of PIN/NIN pins, ensuring the maximum
current of the LED Drivers are not exceeded.
The optical and temperature control loop can be disabled
by I2C setting bits (PINEN & NINEN), or by tying PIN and NIN
pins high (>2.2 V) it is called VSET mode, and the LED Driver
maximum current is set to 50 mA by using a 5.1 k resistor at
the ISET pin.
Current on LED Channel (PIN mode)
Eqn. 3
( VPIN × ICH [ RegisterValue ] )
Current [ A ] = ---------------------------------------------------------------------------------------RSET [ ohms ] × 2
Current on LED Channel (NIN mode)
Eqn. 4
( 2.048 – VNIN ) × ICH [ RegisterValue ]
Current [ A ] = ------------------------------------------------------------------------------------------------------------RSET [ ohms ] × 2
Current on LED Channel (PIN+NIN mode)
Eqn. 5
( 2.048 – VNIN + VPIN ) × ICH [ RegisterValue ]
Current [ A ] = ----------------------------------------------------------------------------------------------------------------------------------RSET [ ohms ] × 2
LED FAILURE PROTECTION
Figure 7. Resistor/Diode placement for multiple open
circuit detection
If the fail pin cannot be cleared by software then it indicates
that the failure is because of t an over-current in the Boost.
Since this is a critical failure the only way to clear it is by
releasing the part from the over-current condition and then
shutdown the part (Refer to Table 5)
Open LED Protection
If LED fails open in any of the LED strings, the voltage in
that channel will be pulled close to zero, which will cause the
channel to be disabled. As a result, the boost output voltage
will go to the OVP level and then come down to the regulation
level to continue powering the rest of the LED strings.
Short LED Protection
If an LED shorted in any of the LED strings, the device will
continue to operate without interruption. However, if the
34844
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Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
shorted LED happens to be in the LED string with the highest
forward voltage, the DHC circuit will automatically regulate
the output voltage with respect to the new highest LED
voltage. If more LEDs are shorted in the same LED string, it
may cause excessive power dissipation in the channel which
may cause the OTT circuit to trip which will completely
shutdown the device.
OVER-TEMPERATURE PROTECTION
The 34844 has an on-chip temperature sensor that
measures die temperature. If the IC temperature exceeds the
OTT threshold, the IC will turn off all power sources inside the
IC (LED drivers, boost and internal regulators) until the
temperature falls below the falling OTT threshold. Once it
comes back on, it will operate with the default configuration
(refer to Table 7).
SERIAL INTERFACE CONTROL
The 34844 uses an I2C interface capable of operating in
standard (100 kHz) or fast (400 kHz) modes.
The A0/SEN pin can be used an address select pin to
allow more than 2 devices in the system. The A0/SEN pin
should be held low on all chips expect the one to be
addressed, where it is taken HIGH.
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Freescale Semiconductor
20
MC34844
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
NORMAL MODE
I 2C
In normal operation the 34844 is programed via
to
drive up to 50 mA of current through each one of the LED
channels. The 34844 can be configured in master or slave
mode as set by the M/~S pin.
In Master mode, the internal PWM generator frequency is
programmed through the I2C interface. The programmed
value sets the number of 25 kHz clocks (40μs) in one PWM
cycle. The 18-bit resolution allows minimum PWM
frequencies of 100 Hz to be programmed. The resulting
frequency is output on the CK pin.
In slave mode, the CK pin acts as an input. The internal
digital PLL uses this frequency as the PWM frequency.
By setting one device as a master, and connecting the CK
output to the input on a number of slave configured devices,
all PWM frequencies are synchronized together. For this
application A0/SEN pin indicates which device is enable for
I2C control.
In Slave mode, an internal phase lock loop will lock the
internal PWM generator period to the period of the signal
present at the CK pin. The PLL can lock to any frequency
from 100 Hz to 25 KHz provided the jitter is below 1000 ppm.
At frequencies above 1.0 KHz, the PLL will maintain lock
regardless of the transient power conditions imposed by the
user (i.e. going from 0% duty cycle to 100% at 20W LED
display power). Below 1.0 kHz, thermal time constants on the
die are such that the PLL may momentarily lose lock if the die
temperature changes substantially during a large load power
step. As explained below, this anomaly can be avoided by
controlling the rate of change in PWM duty cycle.
To better understand this issue, consider that the on chip
PLL uses a VCO that is subject to thermal drift on the order
of 1000 ppm/C. Further consider that the thermal time
constant of the chip is on the order of single digit
milliseconds. Therefore, if a large power load step is imposed
by the user (i.e. going from 0% duty cycle to 100% duty cycle
with a load power of 20 W), the die will experience a large
temperature wave gradient that will propagate across the
chip surface and thereby affect the instantaneous frequency
of the VCO. As long as such changes are within the
bandwidth of the PLL, the PLL will be able to track and
maintain lock. Exceeding this rate of change may cause the
PLL to lose lock and the backlight will momentarily be
blanked until lock is reacquired.
At 100 Hz lock, the PLL has a bandwidth of approximately
10 Hz. This means that temperature changes on the order of
100 ms are tolerable without losing lock. But full load power
changes on the order of 10 ms (i.e. 100 Hz PWM) are not
tracked out and the PLL can momentarily lose lock. If this
happens, as stated above, the LED drivers are momentarily
disabled until lock is reacquired. This will be manifested as a
perceivable short flash on the backlight immediately after the
load change.
To avoid this problem, one can simply limit large
instantaneous changes in die temperature by invoking only
small power steps when raising or lowering the display power
at low PWM frequencies. For example, to maintain lock while
transitioning from 0% to 100% duty cycle at 20 W load power
and a PWM frequency of 100 Hz would entail stepping the
power at a rate not to exceed 1% per 10 ms. If a load of less
than 20 W is used, then the rate of rise can be increased. As
the locked PWM frequency increases (i.e. use 600 Hz
instead of 100 Hz), the step rate can be further increased to
approximately 4% per 2.0 ms. The exact step rate to avoid
loss of PLL lock is a function of essentially three things: (a)
the composite thermal resistance of the user's PCB
assembly, (b) the load power, and (c) the PWM frequency.
For all cases below 1.0 KHz, simply using a rate of 1% duty
cycle change per PWM period will be adequate. If this is too
slow, the value can be optimized experimentally once the
hardware design is complete. At PWM rates above 1.0 KHz,
it is not necessary to control the rate of change in PWM duty
cycle.
It is important to point out that when operating in the
master mode, one does not need to concern themselves with
loss of lock since the reference clock and the VCO clock are
collocated on the die, and therefore experience the same
thermal shift. Hence in master mode, once lock is initially
acquired, it is not lost and no blanking of the display occurs.
The duty cycle of the PWM in both master and slave mode
is set using a second register on the I2C interface.
An external PWM signal can also be applied in the PWM
pin. This pin is AND’ed with the internal signal, giving the
ability to control the duty cycle either via I2C or externally by
setting any of the 2 signals to 100% duty cycle.
STROBE MODE
A strobe mode can be programmed via I2C.
In this mode, each rising edge of the PWM signal turns on
the next channel, while turning off all other channels. The
duration that the channel is illuminated is set by the duty cycle
of the PWM input pin.
This mode can be also programmed by controlling the ON
and OFF state of each LED channel via I2C.
MANUAL MODE
The 34844 can also be used in Manual mode without using
the I2C interface. By setting the pin M/~S High, the LED
dimming will be controlled by the external PWM signal. The
over-voltage protection limit can be settled by a resistor
divider on A0/SEN pin.
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Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DEVICE OPERATION
I2C BUS SPECIFICATION
During manual mode, all internal Registers are in Default
Configuration, refer Table 7, under this configuration the PIN
and NIN pins are enabled to scale the current capability per
string and may be disable by setting 2.2 V in the
corresponding pin.
Also in this mode, the device can be enabled as follows:
+ EN pin + PWM signal (Two Signals): In this
configuration, the PWM signal applied to PWM pin will be in
charge of controlling the LED dimming and a second signal
will enable or disable the chip through the EN pin. Figure 21
+ PWM Signal tied to SDA pin (Just ONE signal): In this
configuration the PWM pin should be tied to SDA pin. The
PWM signal applied to PWM pin will be in charge of
controlling LED dimming and enable the device every time
the PWM is active. For this configuration EN pin should be
LOW.
POWER DOWN MODE
If the input voltage falls below the UVLO threshold, the
device enters automatically into power down mode. When in
power down, the supply current is reduced below 2.0 μA
when there is no I2C activity, and it rises up when I2C
interface is enabled.
I2C BUS SPECIFICATION
The 34844 is a unidirectional device that can only be written by an external control unit. Since the device is a 7 bit address
device (1110110), the control unit needs to follow a specific data transfer format which is shown in Figure 8.
Figure 8. A Complete Data Transfer
For a complete data transfer, please use this format in the
The receiver (34844) must pull down the SDA line during
following order:
this acknowledge pulse to indicate that the data was
correctly written.
1. START condition
• Bits in the first byte: The first seven bits of the first bite
2. The 34844 device address and Write instruction
make up the slave address. The eighth bit is the LSB (least
(R/W = 0)
significant bit), which determines the direction of the
3. First data pack, it corresponds to the 34844 Register
message (Write = 0)
that needs to be written. (refer to Table )
For the 34844 device, when an address is sent, each of the
4. Second data pack, it corresponds to the value that
devices in a system compares the first seven bits after the
should be written to that register. (refer to Table )
START condition with its address. If they match, the
device considers itself addressed by the control unit as a
5. STOP condition
slave-receiver.
I2C variables description:
• STOP: this condition occurs when SDA changes from
LOW to HIGH while SCK is HIGH
• START: this condition occurs when SDA changes from
HIGH to LOW while SCK is HIGH.
For more information about “I2C BUS SPECIFICATION”
please refer to the following link:
• ACKNOWLEDGE: The acknowledge clock pulse is
generated by the Master (Control Unit).
http://www.nxp.com/acrobat_download/literature/
• The transmitter releases the SDA line (HIGH) during the
9398/39340011.pdf
acknowledge clock pulse.
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
22
MC34844
FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
LOGIC COMMANDS AND REGISTERS
Table 6. Write Registers
reg / db
00
D7
D6
OVP3
OVP2
D5
OVP1
D4
D3
OVP0
D2
D1
NINEN
PINEN
EN
CLRI2C
SETI2C
01
D0
04
FPWM5
FPWM4
FPWM3
FPWM2
FPWM1
FPWM0
05
FPWM11
FPWM10
FPWM9
FPWM8
FPWM7
FPWM6
06
FPWM17
FPWM16
FPWM15
FPWM14
FPWM13
FPWM12
DPWM5
DPWM4
DPWM3
DPWM2
DPWM1
DPWM0
CHEN4
CHEN3
CHEN2
CHEN1
CHEN0
CHEN9
CHEN8
CHEN7
CHEN6
CHEN5
BST1
BST0
07
DPWM7
DPWM6
08
09
STRB
CLRFAIL
ALL_OFF
14
F0
ICH0_7
ICH0_6
ICH0_5
ICH0_4
ICH0_3
ICH0_2
ICH0_1
ICH0_0
F1
ICH1_7
ICH1_6
ICH1_5
ICH1_4
ICH1_3
ICH1_2
ICH1_1
ICH1_0
F2
ICH2_7
ICH2_6
ICH2_5
ICH2_4
ICH2_3
ICH2_2
ICH2_1
ICH2_0
F3
ICH3_7
ICH3_6
ICH3_5
ICH3_4
ICHG_3
ICH3_2
ICH3_1
ICH3_0
F4
ICH4_7
ICH4_6
ICH4_5
ICH4_4
ICH4_3
ICH4_2
ICH4_1
ICH4_0
F5
ICH5_7
ICH5_6
ICH5_5
ICH5_4
ICH5_3
ICH5_2
ICH5_1
ICH5_0
F6
ICH6_7
ICH6_6
ICH6_5
ICH6_4
ICH6_3
ICH6_2
ICH6_1
ICH6_0
F7
ICH7_7
ICH7_6
ICH7_5
ICH7_4
ICH7_3
ICH7_2
ICH7_1
ICH7_0
F8
ICH8_7
ICH8_6
ICH8_5
ICH8_4
ICH8_3
ICH8_2
ICH8_1
ICH8_0
F9
ICH9_7
ICH9_6
ICH9_5
ICH9_4
ICH9_3
ICH9_2
ICH9_1
ICH9_0
FA
ICHG_7
ICHG_6
ICHG_5
ICHG_4
ICHG_3
ICHG_2
ICHG_1
ICHG_0
Table 7. Register Description
Register Name
Default Value
(Hex)
EN
1
Chip Enable by software. This signal is ‘OR’ed with external EN (0=off, 1 =on)
PINEN
1
PIN pin enable (0=off, 1 =on)
NINEN
1
NIN pin enable (0=off, 1 =on)
OVP[3:0]
F
OVP voltage
SETI2C
0
SET I2C communication (Disable SM Bus Mode)
CLRI2C
0
Clear set I2C
FPWM[17:0]
300
PWM Frequency
DPWM[7:0]
FF
PWM Duty Cycle (FFh =100%)
CHEN[9:0]
3FF
Channel Enable (0=off, 1=on)
ALL_OFF
0
All 10 channels OFF at the same. In order to reactivate channels this bit should be clear.
CLRFAIL
0
Clear fail if channels are re-enable.
STRB
0
Strobe MODE (0=Parallel, 1=Strobe)
Description
34844
23
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
Table 7. Register Description
Register Name
Default Value
(Hex)
BST[1:0]
2
ICH#[7:0]
FF
Channel Current Program (FFh = Maximum Current)
ICHG[7:0]
FF
Global Current Program
Description
Boost Frequency (150,300,600,1200 kHz) [0h=150 Hz]
Table 8. Over-voltage Protection
REGISTER (HEX)
OVP VALUE (VOLTS)
2
11
3
15
4
19
5
23
6
27
7
31
8
35
9
39
A
43
B
47
C
51
D
55
E
59
F
62
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
24
MC34844
FUNCTIONAL DEVICE OPERATION
TYPICAL PERFORMANCE CURVES (TA=25°C)
TYPICAL PERFORMANCE CURVES (TA=25°C)
95%
94%
93%
Efficiency (%)
92%
91%
90%
Fs = 600KHz
L=22uH, DCR=52mO
Schottky V12P10-E3/86A
COUT = 2x4.7µF, 2x2.2µF/100V
FPWM=600Hz, 100% duty
Load = 16 LEDs, 50mA/channel
VLED = 48V, ±1V /channel
89%
88%
87%
86%
85%
10
12
14
16
18
20
22
24
26
28
30
Vin, volts
Figure 9. Boost efficiency vs Input Voltage
50.50
ILED (highest VLED channel), mA
50.45
Fs = 600KHz
L=22uH, DCR=52mO
Schottky V12P10-E3/86A
COUT = 2x4.7µF, 2x2.2µF/100V
FPWM=600Hz, 100% duty
Load = 16 LEDs, 50mA/channel
V LED = 48V, ±1V /channel
50.40
50.35
50.30
50.25
50.20
50.15
50.10
50.05
50.00
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Vin, volts
Figure 10. Line Regulation, VIN Changing
34844
25
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DEVICE OPERATION
TYPICAL PERFORMANCE CURVES (TA=25°C)
50.0
45.0
50.01 mA
LED Current, mA
40.0
37.59 mA
35.0
30.0
25.0
25.03 mA
20.0
15.0
12.46 mA
10.0
FPWM=25KHz
5.0
0.0
0.4%
0.14 mA
25.0%
50.0%
75.0%
99.6%
PWM Duty Cycle (%)
Figure 11. PWM Dimming Linearity
10.10
10.08
10.06
Bias Current, mA
10.04
10.02
10.00
9.98
9.96
9.94
I2C Mode
SM_Bus Mode
Manual Mode
9.92
9.90
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Vin, volts
Figure 12. Bias Current vs Input Voltage (Operational Mode)
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
26
MC34844
FUNCTIONAL DEVICE OPERATION
TYPICAL PERFORMANCE CURVES (TA=25°C)
3.12
3.10
Bias Current, mA
3.08
3.06
3.04
3.02
I2C Mode
3.00
SM_Bus Mode
2.98
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Vin, volts
Figure 13. Bias Current vs Input Voltage (Sleep Mode)
COMP
Vin=24V
Load=16 LEDs, 50mA/channel
VLED = 47V, ±1V
VOUT
INDUCTOR
CURRENT
Figure 14. Boost Soft Start
34844
27
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
FUNCTIONAL DEVICE OPERATION
TYPICAL PERFORMANCE CURVES (TA=25°C)
ILED, CH1
ISET=40mA (all channels)
FPWM=600Hz, 40% duty
VCH1
VOUT
(ac coupled)
Precharge
INDUCTOR
CURRENT
Figure 15. Typical Operation Waveforms for FPWM=600 Hz, 40% Duty
SWA
SWB
INDUCTOR
CURRENT
VOUT
(ac coupled)
ILED, CH1
ISET=50mA (all channels)
FPWM=600Hz, 100% duty
Figure 16. Typical Operation Waveforms for FPWM=600 Hz, 100% Duty
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
28
MC34844
FUNCTIONAL DEVICE OPERATION
TYPICAL PERFORMANCE CURVES (TA=25°C)
VCh1
ISET = 20mA,
FPWM=20KHz, Duty=0.78% (2LSB)
ILED1
Figure 17. Low Duty Dimming Operation Waveforms (FPWM=20 kHz, 2LSB)
VCh1
ISET = 20mA,
FPWM=20KHz, Duty=0.39% (1LSB)
ILED1
Figure 18. Low Duty Dimming Operation Waveforms (FPWM=20 kHz, 1LSB)
34844
29
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844
TYPICAL APPLICATIONS
TYPICAL APPLICATIONS
MANUAL MODE (Single Wire Control)
22uH
VIN = 24V
1
2
VOUT
U1
1.0K
47uF
1
+
2.2uF
2.2uF
2.2uF
0
56pF
0
5.6K
309K
1.8nF
0
0
CLK
VOUT
0
150K
OVP = 55V
20K
VDC1
5.1K
VDC1
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
32
PGNDA
PGNDB
CK
EN
25
PWM
27
26
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
0
VOUT
VIN
28
31
23
Master CK Output
24
7
SWA
SWB
4
3
2
D1
1
LED MATRIX (16S10P)
13.8uF
+
5
2
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
34844
0
Figure 19. Manual Mode (Single Wire Control)
MANUAL MODE (Two Wire Control)
22uH
VIN = 24V
1
2
VOUT
U2
1.0K
47uF
1
+
2.2uF
2.2uF
0
2.2uF
56pF
0
Control
5.6K
309K
1.8nF
0
EN
PWM
Unit
VOUT
150K
0
OVP = 55V
20K
VDC1
5.1K
VDC1
0
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
Master CK Output
24
7
0
VIN
28
31
23
PWM
27
26
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
VOUT
32
PGNDA
PGNDB
CK
EN
25
SWA
SWB
4
3
34844
2
D5
1
LED MATRIX (16S10P)
13.8uF
+
5
2
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
0
Figure 20. Manual Mode (Two Wire Control)
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
30
MC34844
TYPICAL APPLICATIONS
22uH
VIN = 24V
1
2
VOUT
U3
1.0K
47uF
1
+
2.2uF
2.2uF
0
2.2uF
56pF
0
5.6K
309K
1.8nF
Master CK
0
0
Control
VDC1
0
SCK
SDA
Unit
VDC1
5.1K
VDC1
VIN
28
31
23
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
24
7
CK
EN
25
PWM
27
26
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
0
SWA
SWB
4
3
VOUT
32
D8
2
1
LED MATRIX (16S10P)
13.8uF
+
5
2
PGNDA
PGNDB
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
34844
0
Figure 21. SM Bus Mode
MASTER - SLAVE Connection
22uH
VIN = 24V
1
2
VOUT
U4
1.0K
47uF
1
2.2uF
2.2uF
0
2.2uF
5.6K
56pF
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
24
7
CK
EN
25
PWM
27
26
SCK
SDA
VDC1
6
30
A0/SEN
M/~S
5.1K
19
ISET
20
21
PIN
NIN
309K
1.8nF
0
0
0
Master CK
VDC1
VDC1
0
SWA
SWB
4
3
VOUT
32
VIN
28
31
23
+
PGNDA
PGNDB
2
D1
1
LED MATRIX (16S10P)
13.8uF
+
5
2
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
34844
0
A0/SEN (Master)
A0/SEN (Slave)
MASTER Device
Control
Unit
SDA
SCK
SLAVE Device
VIN = 24V
1
22uH
2
VOUT
U5
1.0K
47uF
1
2.2uF
0
2.2uF
2.2uF
0
56pF
5.6K
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
Master CK
24
7
CK
EN
VDC1
25
PWM
27
26
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
309K
1.8nF
0
0
Input
5.1K
VDC1
0
VIN
28
31
23
+
SWA
SWB
4
3
VOUT
32
PGNDA
PGNDB
34844
2
D2
1
LED MATRIX (16S10P)
13.8uF
+
5
2
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
0
Figure 22. Master - Slave Connection
34844
31
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
MC34844A SPECIFICATIONS PAGES 32 TO 54
MC34844A SPECIFICATIONS
PAGES 32 TO 54
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
32
MC34844A
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
SWA
VIN
SWB
VDC1
LDO
VDC2
A0/SEN
OVP
VDC3
PGNDA
COMP
BOOST
CONTROLLER
SLOPE
PGNDB
VOUT
CK
CLOCK/PLL
EN
V SENSE
FAIL
M/~S
PWM
I0
PWM GENERATOR
I1
I2
SCK
SDA
I2C INTERFACE
10 CHANNEL
80 mA CURRENT
MIRROR
I3
I4
I5
I6
I7
I8
ISET
CURRENT DAC
PIN
TEMP/OPTO
LOOP CONTROL
NIN
I9
OCP/OTP/UVLO
GND
Figure 23. 34844A Simplified Internal Block Diagram
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
33
MC34844A
PIN CONNECTIONS
VOUT
VDC2
M/~S
COMP
VDC1
SCK
SDA
PWM
PIN CONNECTIONS
32
31
30
29
28
27
26
25
VIN 1
24 CK
PGNDB 2
23 VDC3
TRANSPARENT
TOP VIEW
SWB 3
SWA 4
22 SLOPE
21 NIN
QFN - EP
5MM X 5MM
32 LEAD
PGNDA 5
20 PIN
EP GND
A0/SEN 6
19 ISET
EN 7
18 FAIL
IO 8
EP = Exposed Pad
17 I9
9
10
11
12
13
14
15
16
I1
I2
I3
I4
I5
I6
I7
I8
Figure 24. 34844A Pin Connections
Table 9. 34844A Pin Definitions
A functional description of each pin can be found in the Functional Pin Description section beginning on page 42.
Pin Number
Pin Name
Pin Function
Formal Name
Definition
1
VIN
Power
Input voltage
2
PGNDB
Power
Power Ground
Power ground
3
SWB
Input
Switch node B
Boost switch connection B
4
SWA
Input
Switch node A
Boost switch connection A
5
PGNDA
Power
Power Ground
Power ground
6
A0/SEN
Input
Device Select
Address select, device select pin or OVP HW control
7
EN
Input
Enable
8 - 17
I0-I9
Input
LED Channel
18
FAIL
Open Drain
Fault detection
19
ISET
Passive
Current set
20
PIN
Input
Positive current scale
21
NIN
Input
Negative current scale Negative input analog current control
22
SLOPE
Passive
Boost Slope
23
VDC3
Output
Internal Regulator 3
24
CK
Input/Output
Clock signal
25
PWM
Input
External PWM
Input supply
Enable pin (active high, internal pull-up)
LED string connections
Fault detected pin (open drain):
No Failure = Low-impedance
Failure = High-impedance
LED current setting resistor
Positive input analog current control
Boost slope compensation Setting resistor
Decoupling capacitor for internal phase locked loop power
Clock synchronization pin (input for M/~S = low - internal pull-up, output
for M/~S = high)
External PWM input (internal pull-down)
34844A
34
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
PIN CONNECTIONS
Table 9. 34844A Pin Definitions (continued)
A functional description of each pin can be found in the Functional Pin Description section beginning on page 42.
Pin Number
Pin Name
Pin Function
Formal Name
Definition
26
SDA
Bidirectional
I2C data
I2C data Line
27
SCK
Bidirectional
I2C clock
I2C clock line
28
VDC1
Output
Internal Regulator 1
29
COMP
Passive
Compensation pin
30
M/~S
Input
Master/Slave selector
Selects Master mode (1) or Slave mode (0)
31
VDC2
Output
Internal Regulator 2
Decoupling capacitor for internal regulator
32
VOUT
Input
Voltage Output
EP
GND
-
Ground
Decoupling capacitor for internal logic rail
Boost converter Type compensation pin
Boost Output voltage sense pin
Ground Reference for all internal circuits other than Boost FET
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
35
MC34844A
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 10. Maximum Ratings
All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or
permanent damage to the device.
Ratings
Symbol
Value
Unit
ELECTRICAL RATINGS
Maximum Pin Voltages
VMAX
V
A0/SEN
7.0
I0, I1, I2, I3, I4, I5, I6, I7, I8, I9(17)
EN, VIN
45
30
SWA, SWB, VOUT
65
FAIL, PIN, NIN, ISET, M/~S, CK, PWM
6.0
Maximum LED Current
ESD Voltage
(14)
IMAX
85
VESD
mA
V
Human Body Model (HBM)
+2000
Machine Model (MM)
+200
THERMAL RATINGS
Ambient Temperature Range
TA
-40 to 105
°C
Junction to Ambient Temperature(15)
TθJA
32
°C/W
Junction to Case Temperature(15)
TθJC
3.5
°C/W
TJ
150
°C
Storage temperature range
TSTO
-40 to 150
°C
Peak Package Reflow Temperature During Reflow(16)
TPPRT
260
°C
Maximum junction temperature
Power Dissipation
W
TA = 25°C
3.9
TA = 70°C
2.5
TA = 85°C
2.0
TA = 105°C
1.4
Notes
14. ESD testing is performed in accordance with the Human Body Model (HBM) (AEC-Q100-2), and the Machine Model (MM) (AEC-Q100003), RZAP = 0 Ω
15.
16.
17.
Per JEDEC51 Standard for Multilayer PCB
Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may
cause malfunction or permanent damage to the device.
45 V is the Maximum allowable voltage on all LED channels in off-state.
34844A
36
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 11. Static and Dynamic Electrical Characteristics
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1,
-40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
VIN
7.0
12
28
V
SUPPLY
Supply Voltage(20)
Supply Current when Shutdown Mode
μA
ISHUTDOWN
Manual: PWM = Low, EN = Low, SCK & SDA=Low
-
2.0
17
-
-
4.0
-
mA
-
13.0
-
mA
UVLO
5.4
6.0
6.4
V
UVLOHYST
-
300
-
mV
VDC1
2.3
2.5
2.75
V
VDC2
5.5
6.0
6.5
V
VDC3
2.3
2.5
2.75
V
VIN = 7.0 V
VOUT1
8.0
-
28
V
VIN = 28 V
VOUT2
32
-
60
IFET
2.3
2.5
2.7
A
tBOOST_TIME
-
10
-
ms
RDSON of Internal FET (IDRAIN= 1.0 A)
RDSON
-
250
500
mΩ
Boost Switch Off-state Leakage Current
IBOOST_LEAK
-
-
10
μA
Feedback pin Off-state Leakage Current (VOUT = 65 V )
VOUTLEAK
-
500
700
μA
Peak Boost Efficiency(20)
EFFBOOST
-
90
-
%
SM Bus: EN bit = 0, SCK & SDA=Low, EN pin= Low
I2C:
SETI2Cbit=1, CLRI2C=0, EN bit= 0, EN pin = Low
Supply Current when Sleep Mode
ISLEEP
SM-Bus: EN = low, SCK & SDA= Active, SETI2C bit = 0, EN bit = 0
I2C: EN = High, SETI2C bit = 1, CLRI2C bit = 0, EN bit = 0
Supply Current when Operational Mode
IOPERATIONAL
Manual: EN= High, SCK & SDA=Low, PWM=Low
SM-Bus: EN= Low, SCK & SDA=Active, EN bit= 1, PWM=Low
I2C: EN = High, SETI2C bit = 1, CLRI2C bit = 0, EN bit = 1, PWM=Low
Under-voltage Lockout (VIN Rising)
Under-voltage Hysteresis (VIN Falling)
VDC1 Voltage
(18)
CVDC1 = 2.2 μF
VDC2 Voltage(18)
CVDC2 = 2.2 μF
VDC3 Voltage(18)
CVDC3 = 2.2 μF
BOOST
Output Voltage Range(19)(20)
Boost Switch Current Limit
Boost Switch Current Limit Timeout
VSWA,SWB = 65 V
Notes
18. This output is for internal use only and not to be used for other purposes. A 1.0 kΩ resistor between the VDC3 and VDC1 pin is
recommended for <-20 °C operation.
19. Minimum and Maximum output voltages are dependent on Min/Max duty cycle and current limit condition.
20. Guaranteed by design
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
37
MC34844A
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 11. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1,
-40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
IOUT/VIN
-0.2
-
0.2
%/V
IOUT/VLED
-0.2
-
0.2
%/V
VSLOPE
-
0.49
-
V/μs
ACSA
-
9.0
-
Current Sense Resistor
RSENSE
-
22
-
mΩ
OTA Transconductance
GM
-
200
-
μS
Transconductance Sink and Source Current Capability
ISS
-
100
-
μA
IFAIL_LEAK
-
-
50
μA
VOL
-
-
0.4
V
Line Regulation
(21) -
Load Regulation
VIN=7.0 to 28 V
(21) - VLED
= 8.0 to 65 V (all Channels)
Slope compensation voltage ramp - RSLOPE = 68 kΩ
Current Sense Amplifier Gain
FAIL PIN
Off-state Leakage Current - VFAIL = 5.5 V
On-state Voltage Drop - ISINK = 4.0 mA
LED CHANNELS
Sink Current
ISINK
ICHx Register = 255, PIN&NIN = Disabled, TA=25 °C
RISET=3.48 kΩ, 0.1%
Regulated minimum voltage across drivers
Pulse Width > 400 ns
Current Matching Accuracy
ISET Pin Voltage
VMIN
IMATCH
mA
78.4
80
81.6
625
700
775
-2.0
-
2.0
mV
VSET
RISET=3.48 kΩ, 0.1%
%
V
2.007
2.048
2.069
-
1.5
-
ICH_LEAK
-
-
10
μA
VPIN_DIS
2.2
-
-
V
IPIN
-2.0
-
2.0
μA
PIN = VSET/2
36
40
44
mA
PIN = VSET
76
80
84
LED Current Amplitude Resolution
ILEDRES
1.0 mA < ILED < 80 mA
Off-state Leakage Current, All channels - (VCH = 45 V)
%
PIN INPUT
Voltage to Disable PIN mode
PIN Bias Current
PIN = VSET
Analog Dimming Current
IDIM_PIN
ICHx Register = 255, RISET=3.48 kΩ 0.1%
Notes
21. Guaranteed by design
34844A
38
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 11. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1,
-40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
VNIN_DIS
2.2
-
-
V
ININ
-2.0
-
2.0
μA
NIN = VSET/2
36
40
44
mA
NIN = 0 V
76
80
84
150
165
175
-
25
-
NIN INPUT
Voltage to Disable NIN mode
NIN Bias Current
NIN = VSET
Analog Dimming Current
IDIM_NIN
ICHx Register = 255, RISET=3.48 kΩ 0.1%
OVER-TEMPERATURE PROTECTION
Over-temperature Threshold(22)
OTT
Rising
Hysteresis
°C
2
I C/SM BUS PHYSICAL LAYER [SCK, SDA]
I2C Address
ADRI2C
-
1110110
-
Binary
SM-Bus Address
ADRSMB
-
1110110
-
Binary
Input Low Voltage
VILI
-0.3
-
0.8
V
Input High Voltage
VIHI
2.1
-
5.5
V
Input Hysteresis
VHYSI
-
0.3
-
V
Output Low Voltage
Sink Current < 4.0 mA
VOLI
-
-
0.4
V
IINI
-5.0
-
5.0
μA
CINI
-
-
10
ρF
Input Low Voltage
VILL
-0.3
-
0.5
V
Input High Voltage
VIHL
1.5
-
5.5
V
Input Current
Input Capacitance
(22)
LOGIC INPUTS / OUTPUTS (CK, M/~S, PWM, A0/SEN, EN)
Input Hysteresis
VHYSL
-
0.1
-
V
Input Low Voltage (EN)
VILL
-0.3
-
0.5
V
Input High Voltage (EN)
VIHL
2.1
-
28
V
Output Low Voltage (CK)
VOLL
-
-
0.45
V
VOHL
2.2
-
5.5
V
IIIL
-5.0
-
5.0
μA
CINI
-
-
5.0
ρF
ISINK < 2.0 mA
Output High Voltage (CK)
ISOURCE < 2.0 mA
Input Current
Input
Capacitance(22)
Notes
22. Guaranteed by design
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
39
MC34844A
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 11. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1,
-40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
OVP = Fh (Default)
OVPFH
60.5
62.5
64.5
V
OVP = Eh
OVPEH
56.5
58
60
V
OVP = Dh
OVPDH
53
54
56
V
OVP = Ch
OVPCH
49
51
52.5
V
OVP = Bh
OVPBH
45
47
48.5
V
OVP = Ah
OVPAH
41
43
44.5
V
OVP = 9h
OVP9H
38
39
40.5
V
OVP = 8h
OVP8H
34
36
37.5
V
OVP = 7h
OVP7H
30.5
32
33.5
V
OVP = 6h
OVP6H
26
28
30
V
OVP = 5h
OVP5H
23
24
25
V
Over-voltage threshold,
OVPHW
6.15
6.5
6.85
V
ISINK_OVP
70
100
130
μA
Switching Frequency (BST [1:0]=0)
fSW0
0.14
0.16
0.18
MHz
Switching Frequency (BST [1:0]=1) (Default)
fSW1
0.29
0.32
0.35
MHz
Switching Frequency (BST [1:0]=2)
fSW2
0.59
0.65
0.72
MHz
Switching Frequency (BST [1:0]=3)
fSW3
1.17
1.30
1.42
MHz
Boost Switching Frequency
fSW
0.29
0.32
0.35
MHz
Minimum Duty Cycle
DMIN
-
10
15
%
Maximum Duty Cycle
DMAX
80
85
-
%
tSS
-
6.5
-
ms
tTR
-
15
-
ns
tF
-
25
-
ns
OVER-VOLTAGE PROTECTION
Over-voltage Clamp - OVP Register Table:
Set by Hardware, Voltage at A0/SEN
A0/SEN Sink Current, TA=25°C
BOOST
Soft Start Period
Boost Switch Rise Time
Boost Switch Fall Time
(23)
(23)
Notes
23. Guaranteed by design
34844A
40
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
ELECTRICAL CHARACTERISTICS
STATIC AND DYNAMIC ELECTRICAL CHARACTERISTICS
Table 11. Static and Dynamic Electrical Characteristics (continued)
Characteristics noted under conditions VIN = 12 V, VOUT = 42 V, PWM = VDC1, M/~S = VDC1, PIN & NIN = VDC1,
-40°C ≤ TA ≤ 105°C, PGND = 0 V, unless otherwise noted.
Characteristic
Symbol
Min
Typ
Max
Unit
fPWMS
110
-
27000
Hz
25000
27000
29000
Hz
103
110
112
tfPWM
-
0.39
-
%
tPWM_IN
150
-
-
ns
fPWM
110
-
27000
Hz
fCKS
110
-
27000
Hz
fCKS_JITTER
-
-
0.1
%
PWM GENERATOR
PWM Frequency Range (25)
M/~S = Low (Slave Mode)
PWM Frequency
fPWMM
M/~S = High (Master Mode)
FPWM Register = 768
FPWM Register = 192,000
PWM dimming resolution
PWM PIN (DIRECT PWM CONTROL)
Input PWM Pin Minimum Pulse(25)
Input PWM Frequency Range
PHASE LOCK LOOP
CK Slave Mode Frequency Lock Range(24)
M/~S = Low (Slave Mode)
CK Slave Mode Input Jitter(25)
M/~S = Low (Slave Mode)
Slave Mode Acquisition Time
TS_ACQ
M/~S = Low (Slave Mode)
FPWMS=27 kHz
-
50
-
ms
FPWMS=110 Hz
-
2000
-
ms
25000
27000
29000
Hz
103
110
112
CK Frequency (Master Mode)
fCKMASTER
FPWM Register = 768
FPWM Register = 192,000
I2C/SM BUS PHYSICAL LAYER [SCK, SDA]
Interface Frequency Range
fSCK
SM Bus Power-on-Reset Time
tRST
-
tSHUTDOWN
SM Bus Shut down mode Timeout
Output fall
time(25)
400
kHz
100
-
ms
-
30
-
ms
tF
40
-
160
ns
tR
20
-
80
ns
tR/tF
-
25
-
ns
tR/tF
-
23
50
ns
10 ρF < CL < 400 ρF
Output rise time(25)
10 ρF<CL<400 ρF
LOGIC OUTPUT (CK)
Output Rise and Fall time
CL<100 ρF
LED CHANNELS
Channels Rise and Fall Time(25)
Notes
24. Special considerations should be made for frequencies between 110 Hz to 1.0 KHz. Please refer to Functional Device Operation for
further details.
25. Guaranteed by design
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
41
MC34844A
FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
LED backlighting has become very popular for small and
medium LCDs, due to some advantages over other
backlighting schemes, such as the widely used cold cathode
fluorescent lamp (CCFL). The advantages of LED
backlighting are low cost, long life, immunity to vibration, low
operational voltage, and precise control over its intensity.
However, there is an important drawback of this method. It
requires more power than most of the other methods, and this
is a major problem if the LCD size is large enough.
To address the power consumption problem, solid state
optoelectronics technologies are evolving to create brighter
LEDs with lower power consumption. These new
technologies together with highly efficient power
management LED drivers are turning LEDs, a more suitable
solution for backlighting almost any size of LCD panel, with
really conservative power consumption.
One of the most common schemes for backlighting with
LED is the one known as “Array backlighting”. This creates a
matrix of LEDs all over the LCD surface, using defraction and
diffused layers to produce an homogenous and even light at
the LCD surface. Each row or column is formed by a number
of LEDs in series, forcing a single current to flow through all
LEDs in each string.
Using a current control driver, per row or column, helps the
system to maintain a constant current flowing through each
line, keeping a steady amount of light even with the presence
of line or load variations. They can also be use as a light
intensity control by increasing or decreasing the amount of
current flowing through each LED string.
To achieve enough voltage to drive a number of LEDs in
series, a boost converter is implemented, to produce a higher
voltage from a smaller one, which is typically used by the
logical blocks to do their function.
The 34844A implements a single channel boost converter
together with 10 input channels, for driving up to 16 LEDs per
string to create a matrix of more than 160 LEDs. Together
with its 90% efficiency and I2C programmable or external
current control, among other features, makes the 34844A a
perfect solution for backlighting small and medium size LCD
panels, on low power portable and high definition devices.
FUNCTIONAL PIN DESCRIPTION
INPUT VOLTAGE SUPPLY (VIN)
IC ENABLE (EN)
IC Power input supply voltage, is used internally to
produce internal voltage regulation (VDC1, VDC3) for logic
functioning, and also as an input voltage for the boost
regulator.
The active high enable terminal is internally pulled high
through pull-up resistors. Applying 0V to this terminal would
stop the IC from working.
INTERNAL VOLTAGE REGULATOR 1 (VDC1)
This pin is for internal use only, and not to be used for other
purposes. A capacitor of 2.2 μF should be connected
between this pin and ground for decoupling purposes.
INTERNAL VOLTAGE REGULATOR 2 (VDC2)
INPUT/OUTPUT CLOCK SIGNAL (CK)
This terminal can be used as an output clock signal
(master mode), or input clock signal (slave mode), to
synchronize more than one device.
MASTER/SLAVE MODE SELECTION (M/~S)
This pin is for internal use only, and not to be used for other
purposes. A capacitor of 2.2 μF should be connected
between this pin and ground for decoupling purposes.
Setting this pin High puts the device into Master mode,
producing an output synchronization clock at the CK terminal.
Setting this pin low, puts the device in Slave mode, using the
CK pin as an input clock.
INTERNAL VOLTAGE REGULATOR 3 (VDC3)
EXTERNAL PWM INPUT (PWM)
This pin is for internal use only, and not to be used for other
purposes. A capacitor of 2.2 μF should be connected
between this pin and ground for decoupling purposes. A
1.0 kΩ resistor between the VDC3 and VDC1 pin is
recommended for <-20 °C operation.
This terminal is internally pulled down. An external PWM
signal can be applied to modulate the LED channel directly in
absence of an I2C interface.
BOOST COMPENSATION PIN (COMP)
Passive terminal used to compensate the boost converter.
Add a capacitor and a resistor in series to GND to stabilize
the system.
CLOCK I2C SIGNAL (SCK)
Clock line for I2C communication.
ADDRESS I2C SIGNAL (SDA)
Address line for I2C communication.
34844A
42
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
FUNCTIONAL DESCRIPTION
FUNCTIONAL PIN DESCRIPTION
A0/SEN
Address select, device select pin, or Hardware Overvoltage Protection (OVP) Control.
CURRENT SET (ISET)
Each LED string can drive up to 50 mA. The maximum
current can be set by using a resistor from this pin to GND.
POSITIVE CURRENT SCALING (PIN)
Positive current scaling factor for the external analog
current control. Applying 0 V to this pin, scales the current to
near 0%, and in the same way, applying VSET (2.048 V Typ.),
the scale factor is 100%. By applying a voltage higher than
2.2 V, the scaling factor is disabled, and the internal pull-ups
are activated.
If PIN pin and NIN pin are used at the same time then by
applying 0 V to the PIN pin and VSET to NIN pin, scales the
current to near 0%, and in the same way, applying VSET to
the PIN pin and 0 V to NIN pin, scales the current to 100%.
By applying a voltage higher than 2.2 V, the scaling factor is
disabled and the internal pull-ups are activated in both pins.
NEGATIVE CURRENT SCALING (NIN)
Negative current scaling factor for the external analog
current control. Setting 0 V to this pin scales the current to
100%, in the same way, setting VSET (2.048 V Typ.) the scale
factor is near 0%. By applying a voltage higher than 2.2 V, the
scaling factor is disabled and the internal pull-ups are
activated.
If PIN pin and NIN pin are used at the same time then by
applying 0 V to the PIN pin and VSET to NIN pin, scales the
current to near 0%, and in the same way, applying VSET to the
PIN pin and 0 V to NIN pin, scales the current to 100%. By
applying a voltage higher than 2.2 V, the scaling factor is
disabled and the internal pull-ups are activated in both pins.
GROUND (GND)
Ground Reference for all internal circuits other than the
Boost FET.
The Exposed Pad (EP) should be used for thermal heat
dissipation.
I0-I9
Current LED driver, each line has the capability of driving
up to 50 mA.
FAULT DETECTION PIN (FAIL)
When a fault situation is detected, this pin goes into high
impedance.
BOOST SLOPE COMPENSATION SETTING
RESISTOR (SLOPE)
The resistor to be used for the SLOPE depends on the
Input and Output voltage difference as well as the inductor
value. Please use the formula shown in the Components
Calculation section to calculate the value accordingly.
POWER GROUND TERMINALS (PGNDA, PGNDB)
Ground terminal for the internal Boost FET.
OUTPUT VOLTAGE SENSE TERMINAL (VOUT)
Input terminal to monitor the output voltage. It also
supplies the input voltage for the internal regulator 2 (VDC2).
SWITCHING NODE TERMINALS (SWA, SWB)
Switching node of boost converter.
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
43
MC34844A
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
MC34844 - Functional Block Diagram
Regulators / Power Down
Boost
3 Internal Regulators
Protection / Failure Detection
Over-temperature Protection
Over-current Protection
Under-voltage Protection
Over-voltage Protection
LED Open Protection
LED Channels
Logic Control
Optical and Temperature Control
PWM Dimming
Serial Interface Control
Regulator / Power down
Protection / Failure Detection
LED Channels
Logic Control
Boost
Figure 25. Functional Internal Block Diagram
REGULATORS
The 34844A is designed to operate from input voltages in
the 7.0 to 28 V range. This is stepped down internally by
LDOs to 2.5 V (VDC1 and VDC3) and 6 V (VDC3) for
powering internal circuitry. If the input voltage falls below the
UVLO threshold, the device automatically enters in shut
down mode.
Power UP Sequence:
The power up sequence for applying VIN, with respect to
the ENABLE and PWM signals, is very important to assure a
good performance of the part.
It is recommended to follow this sequence:
1. Apply VIN first
2. Wait for a couple of milliseconds (~2.0 ms) to let the
logic and internal regulators get settled
3. Take the EN pin high, or keep it low depending on the
operating mode
4. Apply the PWM signal
Operating Modes:
The device can be operated by the EN pin and/or SDA/
SCK bus lines, resulting in three distinct operation modes:
• Manual mode, there is no I2C capability, the bus line pins
must be tied low, and the EN pin controls the ON/OFF
operation. To shutdown the part in Manual mode, first the
PWM pin should be taken low followed by the EN pin. The
part will not shut down unless VOUT collapses to a voltage
below 30 V.
• SM Bus mode, EN pin must be tied low and the device is
turned ON by any activity on the bus lines. The part shuts
down if the bus lines are held low for more than 30 ms, the
30 ms watchdog timer can be disabled by I2C (setting
SETI2C bit high) or tying the EN pin high. In Sleep mode
(EN bit=0) the device reduces the power consumption by
leaving “alive” only the blocks required for I2C
communication.To shutdown the part in SM Bus mode, the
EN bit should first be a '0', then the SCK and SDA should
be taken low.
• I2C mode, has to be configured by I2C communication
(SETI2C bit = 1) right after the IC is turned ON, it prevents
the part from being turned ON/OFF by the bus. Sleep
mode is also present and it is intended to save power, but
still keep the IC prepared to communicate by I2C. By
taking the EN bit low and then the EN pin low, the part
enters into a shutdown mode.
34844A
44
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Table 12. Operation Current Consumption Modes
MODE
Manual
SM Bus
EN Pin
SCK/SDA Pins
I2C Bit Command
Current Consumption
Mode
Comments
Low
Low
N/A
Shutdown
PWM pin = Low
High
Low
N/A
Operational
Low
Low (> 27 ms)
EN bit = 0
Shutdown
Low
Active
EN bit = 0
Sleep
Low
Active
EN bit = 1
Operational
Low
X
CLRI2C bit = 0
SETI2C bit = 1
I2C Low Power
(Shutdown)
Part Doesn’t
Wake-up
EN bit = 0
SETI2C bit = 1
I2 C
High
X
CLRI2C bit = 0
Sleep
EN bit = 0
SETI2C bit = 1
High
X
CLRI2C bit = 0
Operational
EN bit = 1
BOOST
The integrated boost converter operates in nonsynchronous mode and integrates a 2.5 A FET. An integrated
sense circuit is used to sense the voltage at the LED current
mirror inputs and automatically sets the boost output voltage
(DHC) to the minimum voltage needed to keep all LEDs
biased with the required current. The DHC is designed to
operate for pulse widths > 400 ns in the LED drivers.
If the pulse widths are shorter than specified, the DHC
circuit will not operate and the voltage across the LED drivers
will increase to a value given by the OVP minus the total LED
voltage in the LED string. Therefore it is imperative to select
the proper OVP level to minimize power dissipation.
The user can program the boost frequency by I2C
(BST[1:0]) only after the IC is powered up and before the
boost circuit is turned ON for the first time (PWM pin low to
high). This sequence avoids boost frequency to be changed
inadvertently during operation. The first I2C command has to
wait for 5.0 ms after the part is turned ON, in order to allow
sufficient time for the device power up sequence to be
completed.
Please follow this sequence in order to change the Boost
frequency thru I2C:
1. Take PWM pin low
2. Disable the part by software (EN bit = low)
3. Write the new Boost frequency data (BST[1:0])
normal quiescent operating temperature and thereby
experience a forward voltage change, typically an increase in
the forward voltage. This change can be significant for
applications with a large number of series LEDs in a string
operating at high current. If the boost controller did not track
this increased change, the potential on the LED drivers would
saturate for a few cycles once the LED channels are reenabled.
HARDWARE AND SOFTWARE OVP:
The OVP value should be set to a higher value than the
maximum LED voltage over the whole temperature range. A
good practice is to set it 5.0 V or so above the max LED
voltage.
The OVP can be set from 11 to 62 V, ~4.0 V spaced, using
the I2C interface (OVP Register). If the I2C capability is not
present, the OVP can be controlled either by a resistor divider
connected from VOUT to GND, with its mid point tied to the
A0/SEN pin, or by a zener diode from VOUT to the A0/SEN
pin (threshold = 6.5 V). During an OVP condition, the output
voltage will go to the OVP level, which is programmed via the
I2C interface or settled by a resistor divider on A0/SEN pin, or
by a zener diode. The formulas to calculate the hardware
OVP using any of the two methods are as follows:
Method 1
VOUT
4. Enable the part by software (EN bit = high)
5. Reconfigure all registers
6. Take PWM pin High
The boost controller has an integral track and hold
amplifier with indefinite hold time capability, to enable
immediate LED on cycles after extended off times. During
extended off times, the external LEDs cool down from their
Method 2
VOUT
RUPPER
A0/SEN
RLOWER
VZENER2
A0/SEN
OVP = VZENER2 + 6.5 V
OVP = 6.5 V [(RUPPER / RLOWER) + 1] + (100E-6 x RUPPER)
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
45
MC34844A
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
OVER-CURRENT PROTECTION (OCP)
The boost converter also features internal Over-current
Protection (OCP) and has a user programmable Overvoltage Protection (OVP).
The OCP operates on a cycle by cycle basis. However, if
the OCP condition remains for more than 10ms then the
device turns off the LED Drivers, the Boost goes to Sleep
mode and the output FAULT pin goes into high-impedance.
The device can only be restarted by recycling the enable or
creating a Power On Reset (POR).
CURRENT MIRROR
The programmable current mirror matches the current in
10 LED strings to within 2%. The maximum current is set
using a resistor to GND from the ISET pin. This can be scaled
down using the I2C interface to 255 levels.
Zero current is achieved by turning off the LED Driver by
I2C (registers CHENx = 0h) for a duty cycle from 0% to 99%,
or by pulling PWM pin low regardless of the duty cycle.
I2C capability allows the channels to be controlled
individually or in parallel.
Current on LED Channel (PIN and NIN mode disabled)
VSET [ V ] × 136
ISINK [ A ] = -------------------------------------------RISET [ Ω ]
×
Eqn. 6
ICH [ RegisterValue ]
----------------------------------------------------------255
Default ICH[RegisterValue]=255
In the off state, the LEDs current is set to 0 and the boost
converter stops switching.
This feature allows to drive more than 80 mA of current by
connecting the LED string to 2 or more LED channels in
parallel. For example; if the application requires to drive a
channels at 160 mA, then the bottom of each LED string
should be connected to two channels in order to duplicate the
current capability (Example: CH0+CH1 = 160 mA).
The duty cycle of the PWM waveform in both master and
slave modes is set using a second register on the I2C
interface (register DPWM), and can be controlled from 100%
duty cycle to 1/256 Tpwm = 0.39%. Zero percent of duty cycle
is achieved by turning LED drivers off (register CHENx = 0h)
or pulling PWM pin low.
An external PWM can also be used. The PWM input is
'AND'ed with the internal signal. By setting the serial interface
to 100% duty cycle (default), the external pin has full control
of the PWM duty cycle. This pin can also be used to modulate
the LED at a lower frequency than the PWM dimming
frequency (DHC Minimum pulse width = 400 ns).
POWER OFF AND POWER ON LED CHANNELS
The 34844A allows the user to Power OFF and Power ON
any channel independently thru I2C/SM-BUS mode.
The POWER ON function reconnects the LED driver and
the feedback circuit to the channel to allow functionality to
that channel again.
On an opposite way when the channel is POWER OFF,
the LED driver and feedback circuit are disconnected to the
channels.
This function is very useful for applications where one or
more channel has to be shutdown to avoid the output
voltages goes to OVP during the start up of the part.
The sequence to make these functions work is the
following:
To POWER ON LED channels:
1. Take PWM pin low
2. Set POWER ON bit high (MSB of Register 09)
3. Set high all Channels that should be power on by
writing “1” on CHENx bits (Registers 08 & 09)
4. Clear POWER ON bit
5. Take PWM pin high
PWM GENERATOR
The PWM generator can operate in either master or slave
modes, as set by the M/~S pin.
In master mode, the internal PWM generator frequency is
programmed through the I2C interface (registers FPWM).
The default programmed value set the number of 27 kHz
clocks (40 μs) in one PWM cycle. The 18-bit resolution allows
minimum PWM frequencies of 110 Hz to be programmed.
The resulting frequency is output on the CK pin.
PWM Frequency
To POWER OFF LED channels:
1. Take PWM pin low
2. Set POWER OFF bit high (MSB of Register 08)
3. Clear all Channels that should be power off by writing
“0” on CHENx bits (Registers 08 & 09)
4. Clear POWER OFF bit
5. Take PWM pin high
Eqn. 7
20.736Mhz
FPWM [ Hz ] = -------------------------------------------------------------------FPWM [ RegisterValue ]
In slave mode, the CK pin acts as an input. The internal
digital PLL uses this frequency as the PWM frequency. By
setting one device as master, and connecting the CK output
to the input on a number of slave configured devices, all
PWM frequencies are synchronized together.
POWER ON bit and POWER OFF bit shouldn’t be set at
the same time in order to avoid damage to the part.
POWER ON/OFF channels should be reconfigured every
time the part gets recovered from a POR or shutdown
condition. This also apply if the part is reenabled by software.
If the part is reenabled by software, it is recommended to
take PWM pin low, reenable the part and then follow the
corresponding sequence shown above.
34844A
46
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
DISABLING LED CHANNELS
The 34844A allows the user to enable and disable each of
the 10 channels separately by writing the corresponding
CHENx bit on Registers 08 and 09 thru I2C.
Since the enable and disable functions reconnects the
feedback circuit of the LED drivers, this shouldn’t be used on
any channel that shuts down either because an open LED
channel condition or because is was previously POWER
OFF. This could cause instability issues since the voltage on
this open LED driver is not substantially above the DHC
regulation voltage (0.75 V typ) and may interfere with the
operation of the dynamic headroom control (DHC) which can
lead to erratic output voltage regulation
FAIL PIN
If a LED fails open in any of the LED strings, the voltage in
that particular LED channel will be close to ground and the
LED open failure is detected. When this happens, a failure is
registered, the FAIL pin is set to its high-impedance stage,
and the channel is shut down.
The FAIL pin cannot be cleared for manual mode unless a
complete power on reset is applied.
However for I2C/SMBUS mode, the FAIL pin can be
cleared by cycling the clear fail bit (CLRFAIL bit = 0 - 1 - 0).
This allows the user to waive any known failure and set the
device for being able to detect any other failure during
operation.
If the fail pin cannot be cleared by software then it indicates
that the failure is because of an over-current in the Boost.
Since this is a critical failure the only way to clear it is by
releasing the part from the over-current condition and then
shutdown the part (Refer to Table 12)
If I2C communication is not present, FAIL condition should
be reset by removing the failure and re-enabling the device
thru the EN pin.
OPTICAL AND TEMPERATURE CONTROL LOOP
The 34844A supports both optical and temperature loop
control.
For temperature loop control, the LED brightness can be
adjusted depending on the temperature of the LEDs.
For optical loop control, the 34844A supports both optical
closed loop backlight control, where the brightness of the
backlight is maintained at a required level by adjusting the
light output, until the desired level is achieved, or with
ambient light control, where the backlight brightness
increases as ambient light increases.
Both temperature and optical loops are supported through
the PIN and NIN pins. Each pin supports a 0 V to VSET
(2.048 V typ.) input range which affects the current through
the LEDs. The PIN pin increases current as the voltage rises
from 0 to VSET. The NIN pin reduces current as the voltage
rises from 0 - VSET.
A 6.98 kohm resistor or higher value must be used at the
ISET pin if the part is configured to use PIN+NIN control loop
functionality, the 80 mA maximum current is achieved at the
higher allowed level of PIN/NIN pins, ensuring the maximum
current of the LED Drivers are not exceeded.
The optical and temperature control loop can be disabled
by I2C setting bits (PINEN & NINEN), or by tying PIN and NIN
pins high (>2.2 V). The LED Driver maximum current is set to
80 mA by using a 3.48 kohm resistor at the ISET pin.
Current on LED Channel (PIN mode)
VPIN [ V ]
IDIM [ A ] = ISINK [ A ] × -----------------------2
Eqn. 8
Current on LED Channel (NIN mode)
Eqn. 9
IDIM [ A ] = ISINK [ A ]
×
( VSET – VNIN ) [ V ]
---------------------------------------------------2
Current on LED Channel (PIN+NIN mode)
IDIM [ A ] = ISINK [ A ]
×
Eqn. 10
( VSET + VPIN – VNIN ) [ V ]
-------------------------------------------------------------------------2
VPIN and VNIN is the voltage applied on PIN and NIN pins
correspondingly.
For ISINK formula please refer to Equation 1.
LED FAILURE PROTECTION
Open LED Protection
If LED fails open in any of the LED strings, the voltage in
that channel will be pulled close to zero, which will cause the
channel to be disabled. As a result, the boost output voltage
will go to the OVP level and then come down to the regulation
level to continue powering the rest of the LED strings.
Short LED Protection
If an LED shorted in any of the LED strings, the device will
continue to operate without interruption. However, if the
shorted LED happens to be in the LED string with the highest
forward voltage, the DHC circuit will automatically regulate
the output voltage with respect to the new highest LED
voltage. If more LEDs are shorted in the same LED string, it
may cause excessive power dissipation in the channel which
may cause the OTT circuit to trip which will completely
shutdown the device.
OVER-TEMPERATURE PROTECTION
The 34844A has an on-chip temperature sensor that
measures die temperature. If the IC temperature exceeds the
OTT threshold, the IC will turn off all power sources inside the
IC (LED drivers, boost and internal regulators) until the
temperature falls below the falling OTT threshold. Once it
comes back on, it will operate with the default configuration
(refer to Table 14).
SERIAL INTERFACE CONTROL
The 34844A uses an I2C interface capable of operating in
standard (100 kHz) or fast (400 kHz) modes.
The A0/SEN pin can be used an address select pin to
allow more than 2 devices in the system. The A0/SEN pin
should be held low on all chips expect the one to be
addressed, where it is taken HIGH.
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
47
MC34844A
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
NORMAL MODE
In normal operation the 34844A is programed via I2C to
drive up to 50 mA of current through each one of the LED
channels. The 34844A can be configured in master or slave
mode as set by the M/~S pin.
In Master mode, the internal PWM generator frequency is
programmed through the I2C interface. The programmed
value sets the number of 27 kHz clocks (37μs) in one PWM
cycle. The 18-bit resolution allows minimum PWM
frequencies of 110 Hz to be programmed. The resulting
frequency is output on the CK pin.
In slave mode, the CK pin acts as an input. The internal
digital PLL uses this frequency as the PWM frequency.
By setting one device as a master, and connecting the CK
output to the input on a number of slave configured devices,
all PWM frequencies are synchronized together. For this
application A0/SEN pin indicates which device is enable for
I2C control.
In Slave mode, an internal phase lock loop will lock the
internal PWM generator period to the period of the signal
present at the CK pin. The PLL can lock to any frequency
from 110 Hz to 27 KHz provided the jitter is below 1000 ppm.
At frequencies above 1.0 KHz, the PLL will maintain lock
regardless of the transient power conditions imposed by the
user (i.e. going from 0% duty cycle to 100% at 20W LED
display power). Below 1.0 kHz, thermal time constants on the
die are such that the PLL may momentarily lose lock if the die
temperature changes substantially during a large load power
step. As explained below, this anomaly can be avoided by
controlling the rate of change in PWM duty cycle.
To better understand this issue, consider that the on chip
PLL uses a VCO that is subject to thermal drift on the order
of 1000 ppm/C. Further consider that the thermal time
constant of the chip is on the order of single digit
milliseconds. Therefore, if a large power load step is imposed
by the user (i.e. going from 0% duty cycle to 100% duty cycle
with a load power of 20 W), the die will experience a large
temperature wave gradient that will propagate across the
chip surface and thereby affect the instantaneous frequency
of the VCO. As long as such changes are within the
bandwidth of the PLL, the PLL will be able to track and
maintain lock. Exceeding this rate of change may cause the
PLL to lose lock and the backlight will momentarily be
blanked until lock is reacquired.
At 110 Hz lock, the PLL has a bandwidth of approximately
10 Hz. This means that temperature changes on the order of
100 ms are tolerable without losing lock. But full load power
changes on the order of 10 ms (i.e. 110 Hz PWM) are not
tracked out and the PLL can momentarily lose lock. If this
happens, as stated above, the LED drivers are momentarily
disabled until lock is reacquired. This will be manifested as a
perceivable short flash on the backlight immediately after the
load change.
To avoid this problem, one can simply limit large
instantaneous changes in die temperature by invoking only
small power steps when raising or lowering the display power
at low PWM frequencies. For example, to maintain lock while
transitioning from 0% to 100% duty cycle at 20 W load power
and a PWM frequency of 110 Hz would entail stepping the
power at a rate not to exceed 1% per 10 ms. If a load of less
than 20 W is used, then the rate of rise can be increased. As
the locked PWM frequency increases (i.e. use 600 Hz
instead of 110 Hz), the step rate can be further increased to
approximately 4% per 2.0 ms. The exact step rate to avoid
loss of PLL lock is a function of essentially three things: (a)
the composite thermal resistance of the user's PCB
assembly, (b) the load power, and (c) the PWM frequency.
For all cases below 1.0 KHz, simply using a rate of 1% duty
cycle change per PWM period will be adequate. If this is too
slow, the value can be optimized experimentally once the
hardware design is complete. At PWM rates above 1.0 KHz,
it is not necessary to control the rate of change in PWM duty
cycle.
It is important to point out that when operating in the
master mode, one does not need to concern themselves with
loss of lock since the reference clock and the VCO clock are
collocated on the die, and therefore experience the same
thermal shift. Hence in master mode, once lock is initially
acquired, it is not lost and no blanking of the display occurs.
The duty cycle of the PWM in both master and slave mode
is set using a second register on the I2C interface.
An external PWM signal can also be applied in the PWM
pin. This pin is AND’ed with the internal signal, giving the
ability to control the duty cycle either via I2C or externally by
setting any of the 2 signals to 100% duty cycle.
MANUAL MODE
The 34844A can also be used in Manual mode without
using the I2C interface. By setting the pin M/~S High, the LED
dimming will be controlled by the external PWM signal. The
over-voltage protection limit can be settled by a resistor
divider or a zener diode on A0/SEN pin.
During manual mode, all internal Registers are in Default
Configuration, refer Table 14, under this configuration the
PIN and NIN pins are enabled to scale the current capability
per string and may be disable by setting 2.2 V in the
corresponding terminal.
Also in this mode, the device can be enabled as follows:
• EN pin + PWM signal (Two Signals):
In this configuration, the PWM signal applied to PWM pin
will be in charge of controlling the LED dimming and a second
signal will enable or disable the chip through the EN pin.
• PWM Signal tied to SDA pin (Just ONE signal):
In this configuration the PWM pin should be tied to the
SDA pin. The PWM signal applied to PWM pin will be in
34844A
48
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
FUNCTIONAL DEVICE OPERATION
I2C BUS SPECIFICATION
charge of controlling LED dimming and enabling the device
every time the PWM is active. For this configuration the EN
pin should be LOW.
I2C BUS SPECIFICATION
The 34844A is a unidirectional device that can only be written by an external control unit. Since the device is a 7 bit address
device (1110110), the control unit needs to follow a specific data transfer format which is shown in Table 26.
Figure 26. A Complete Data Transfer
For a complete data transfer, please use this format in the
down the SDA line during this acknowledge pulse to
following order:
indicate that the data was correctly written.
•
Bits
in the first byte: The first seven bits of the first bite
1. START condition
make up the slave address. The eighth bit is the LSB (least
2. 34844A device address and Write instruction (R/W = 0)
significant bit), which determines the direction of the
3. First data pack, it corresponds to the 34844A register
message (Write = 0)
that needs to be written. (refer to Table 13)
For the 34844A device, when an address is sent, each of
4. Second data pack, it corresponds to the value that
the devices in a system compares the first seven bits after
should be written to that register. (refer to Table 13)
the START condition with its address. If they match, the
device considers itself addressed by the control unit as a
5. STOP condition
slave-receiver.
• STOP: this condition occurs when SDA changes from
I2C variables description:
LOW to HIGH while SCK is HIGH
• START: this condition occurs when SDA changes from
For more information about “I2C BUS SPECIFICATION”
HIGH to LOW while SCK is HIGH.
please refer to the following link:
• ACKNOWLEDGE: The acknowledge clock pulse is
generated by the Master (Control Unit).
http://www.nxp.com/acrobat_download/literature/
• The transmitter releases the SDA line (HIGH) during the
9398/39340011.pdf
acknowledge clock pulse.The receiver (34844A) must pull
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
49
MC34844A
FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
LOGIC COMMANDS AND REGISTERS
Table 13. Write Registers
reg / db
D7
D6
OVP3
00
OVP2
D5
OVP1
D4
D3
OVP0
D2
NINEN
01
D1
D0
PINEN
EN
CLRI2C
SETI2C
04
FPWM5
FPWM4
FPWM3
FPWM2
FPWM1
FPWM0
05
FPWM11
FPWM10
FPWM9
FPWM8
FPWM7
FPWM6
06
FPWM17
FPWM16
FPWM15
FPWM14
FPWM13
FPWM12
DPWM5
DPWM4
DPWM3
DPWM2
DPWM1
DPWM0
CHEN4
CHEN3
CHEN2
CHEN1
CHEN0
CHEN9
CHEN8
CHEN7
CHEN6
CHEN5
BST1
BST0
07
DPWM7
DPWM6
08
PWR_OFF
09
PWR_ON
CLRFAIL
ALL_OFF
14
F0
ICH0_7
ICH0_6
ICH0_5
ICH0_4
ICH0_3
ICH0_2
ICH0_1
ICH0_0
F1
ICH1_7
ICH1_6
ICH1_5
ICH1_4
ICH1_3
ICH1_2
ICH1_1
ICH1_0
F2
ICH2_7
ICH2_6
ICH2_5
ICH2_4
ICH2_3
ICH2_2
ICH2_1
ICH2_0
F3
ICH3_7
ICH3_6
ICH3_5
ICH3_4
ICHG_3
ICH3_2
ICH3_1
ICH3_0
F4
ICH4_7
ICH4_6
ICH4_5
ICH4_4
ICH4_3
ICH4_2
ICH4_1
ICH4_0
F5
ICH5_7
ICH5_6
ICH5_5
ICH5_4
ICH5_3
ICH5_2
ICH5_1
ICH5_0
F6
ICH6_7
ICH6_6
ICH6_5
ICH6_4
ICH6_3
ICH6_2
ICH6_1
ICH6_0
F7
ICH7_7
ICH7_6
ICH7_5
ICH7_4
ICH7_3
ICH7_2
ICH7_1
ICH7_0
F8
ICH8_7
ICH8_6
ICH8_5
ICH8_4
ICH8_3
ICH8_2
ICH8_1
ICH8_0
F9
ICH9_7
ICH9_6
ICH9_5
ICH9_4
ICH9_3
ICH9_2
ICH9_1
ICH9_0
FA
ICHG_7
ICHG_6
ICHG_5
ICHG_4
ICHG_3
ICHG_2
ICHG_1
ICHG_0
All registers and POWER ON/OFF channels should be
reconfigured every time the part gets recovered from a POR
or shutdown condition.
The configuration sequence every time the part is power
up should be as follows:
1. Take the PWM pin low
2. Power up the part
3. Configure all registers
For configuring the part once in operation it is
recommended to follow this sequence:
1. Take the PWM pin low
2. Configure the registers
3. Take the PWM pin High
Special considerations should be taken for re-configuring
POWER ON/OFF functions, please refer to the POWER OFF
and POWER ON LED CHANNELS section.
4. Take the PWM pin High
Table 14. Register Description
Register Name
Default Value
(Hex)
EN
1
Chip Enable by software.
PINEN
1
PIN pin enable (0=off, 1 =on)
NINEN
1
NIN pin enable (0=off, 1 =on)
OVP[3:0]
F
OVP voltage
SETI2C
0
SET I2C communication (Disable SM Bus Mode)
CLRI2C
0
Clear set I2C
Description
34844A
50
Analog Integrated Circuit Device Data
Freescale Semiconductor
MC34844A
FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
Table 14. Register Description
Register Name
Default Value
(Hex)
FPWM[17:0]
300
PWM Frequency
DPWM[7:0]
FF
PWM Duty Cycle (FFh =100%)
CHEN[9:0]
3FF
Channel Enable (0=off, 1=on)
ALL_OFF
0
All 10 channels OFF at the same. In order to reactivate channels this bit should be clear.
CLRFAIL
0
Clear fail if channels are re-enable.
PWR_OFF
0
POWER OFF LED channels (0=disable, 1=enable)
PWR_ON
0
POWER ON LED channels (0=disable, 1=enable)
BST[1:0]
2
Boost Frequency (160,320,650,1300 kHz) [0h=160 Hz]
ICH#[7:0]
FF
Channel Current Program (FFh = Maximum Current)
ICHG[7:0]
FF
Global Current Program
Description
Table 15. Over-voltage Protection
Register (hex)
OVP Value (vOLTS)
2
11
3
15
4
19
5
23
6
27
7
31
8
35
9
39
A
43
B
47
C
51
D
55
E
59
F
62
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
51
MC34844A
TYPICAL APPLICATIONS
TYPICAL APPLICATIONS
MANUAL MODE (Single Wire Control)
22uH
VIN = 24V
1
2
1.0K
47uF
1
+
2.2uF
2.2uF
0
2.2uF
56pF
0
5.6K
309K
1.8nF
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
Master CK Output
24
7
0
0
CLK
VOUT
VIN
28
31
23
0
150K
OVP = 55V
20K
VDC1
5.1K
VDC1
PWM
27
26
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
0
SWA
SWB
4
3
VOUT
32
D1
2
1
13.8uF
+
5
2
PGNDA
PGNDB
CK
EN
25
LED MATRIX (16S10P)
VOUT
U1
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
34844
0
Figure 27. Manual Mode (Single Wire Control)
Conditions: VIN = 24 V, VOUT = 47 V, Load = 16S10P, ILED = 60 mA, OVP = 53V, fSW = 300 kHz
MANUAL MODE (Two Wire Control)
22uH
VIN = 24V
1
2
VOUT
U2
1.0K
47uF
1
+
2.2uF
2.2uF
0
2.2uF
56pF
0
Control
5.6K
309K
1.8nF
0
PWM
Unit
VOUT
150K
0
OVP = 55V
20K
VDC1
5.1K
VDC1
0
VDC1
VDC2
VDC3
29
22
COMP
SLOPE
Master CK Output
24
7
0
EN
VIN
28
31
23
PWM
27
26
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
4
3
32
PGNDA
PGNDB
CK
EN
25
SWA
SWB
VOUT
34844
2
D5
1
LED MATRIX (16S10P)
13.8uF
+
5
2
FAIL
18
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
8
9
10
11
12
13
14
15
16
17
GND
33
VCC
3.3K
0
0
Figure 28. Manual Mode (Two Wire Control)
Conditions: VIN = 24 V, VOUT = 47 V, Load = 16S10P, ILED = 60 mA, OVP = 53V, fSW = 300 kHz
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
52
MC34844A
TYPICAL APPLICATIONS
I2C MODE (Master Mode)
1
VIN = 24V
1
+
10uF
2.2uF
2.2uF
0
5.6K
OUTPUT
0
MASTER CK
VDC1
0
24
7
25
CONTROL UNIT
VDC1
4.64K
ISET = 60mA
VDC1
SCK
SDA
6
30
A0/SEN
M/~S
19
ISET
20
21
PIN
NIN
0
8
9
10
11
12
13
14
15
16
17
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
4.7uF
VCC
18
FAIL
PWM
27
26
+
30uF
5
2
PGNDA
PGNDB
CK
EN
1
32
VOUT
COMP
SLOPE
D533
2
4
3
SWA
SWB
VDC1
VDC2
VDC3
29
22
100K
100pF
EN_Master
SCK
SDA
A0SEN_Master
LED MATRIX (16S10P)
VOUT
VIN
28
31
23
4700pF
2.2uF
0
2
U9
1.0K
47uF
47uH
0
3.3K
220pF
33
GND
MC34844A
220pF
0
220pF
220pF
220pF
220pF
* FOR I2C MODE - SETI2C bit should be set High.
* FOR SM-BUS MODE - EN pin should be connected to
GND or taken low by the Control Unit.
220pF
220pF
220pF
220pF
0
Figure 29. I2C (Master Mode)
Conditions: VIN = 24 V, VOUT = 47 V, Load = 16S10P, ILED = 60 mA, OVP = 53V, fSW = 300 kHz
I2C MODE (Slave Mode)
1
VIN = 24V
1
+
10uF
2.2uF
0
2.2uF
28
31
23
4700pF
2.2uF
0
5.6K
100K
100pF
EN_Slave
SCK
SDA
A0SEN_Slave
2
LED MATRIX (16S10P)
VOUT
U11
1.0K
47uF
47uH
0
0
INPUT
VDC1
MASTER CK
29
22
24
7
25
27
26
6
30
CONTROL UNIT
0
4.64K
ISET = 60mA
VDC1
0
19
20
21
VIN
VDC1
VDC2
VDC3
COMP
SLOPE
SWA
SWB
VOUT
PGNDA
PGNDB
CK
EN
FAIL
PWM
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
SCK
SDA
A0/SEN
M/~S
ISET
PIN
NIN
GND
4
3
2
D553
1
+
32
30uF
5
2
VCC
18
8
9
10
11
12
13
14
15
16
17
3.3K
MC34844A
0
220pF
33
* FOR I2C MODE - SETI2C bit should be set High.
* FOR SM-BUS MODE - EN pin should be connected to
GND or taken low by the Control Unit.
4.7uF
0
220pF
220pF
220pF
220pF
220pF
220pF
220pF
220pF
220pF
0
Figure 30. I2C (Slave Mode)
Conditions: VIN = 24 V, VOUT = 47 V, Load = 16S10P, ILED = 60 mA, OVP = 53V, fSW = 300 kHz
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
53
MC34844A
TYPICAL APPLICATIONS
LED MATRIX (40S8P)
1
150UH
PDS3200
VIN = 60V to 72V
2
1
VDC2
1.0k
2.2uF
EN_DLY
1
0
2.2uF
3.3nF
100pF
0
0
2.2uF
28
31
23
200k
0 EN_DLY
6.8K
VOUT
PWM = 200Hz (5V)
0
270K
4.64K
OVP = 125V
18K
0
24
7
25
27K
0
29
22
ISET =
60mA
VDC1
27
26
6
30
19
VDC1
20
21
VDC1
VDC2
VDC3
COMP
SLOPE
CK
EN
PWM
SCK
SDA
A0/SEN
M/~S
ISET
PIN
NIN
MC34844A
SWA
SWB
VOUT
PGNDA
PGNDB
FAIL
I0
I1
I2
I3
I4
I5
I6
I7
I8
I9
GND
1
2
82V
MMSZ5268BT1G
10uF
250V
+
10uF
250V
+
10uF
250V
+
220pF
220pF
1uF
250V
2
1
VIN
3
0
4
2
0.1UF
0.1UF
100V
2.2uF
8
10
FDS2572
47V
3SMBJ5941B-TP
0
7
10uF
100V
+
6
5
7447709151
47uF
100V
10.0K
VOUT = 120V
3
4
3
32
5
2
18
0
8
9
10
11
12
13
14
15
16
17
33
0
220pF
220pF
220pF
220pF
220pF
220pF
0
Figure 31. HIGH VOUT application (Manual Mode)
Conditions: VIN = 60 to 72V, VOUT = 120 V, Load = 40S8P, ILED = 60 mA, OVP = 125 V, fSW = 300 kHz
34844A
Analog Integrated Circuit Device Data
Freescale Semiconductor
54
COMPONENTS CALCULATION
COMPONENTS CALCULATION
The following formulas are intended for the calculation of
all external components related with the Boost converter and
Network compensation.
In order to calculate a Duty Cycle, the internal losses of the
MOSFET and Diode should be taken into consideration.
Vout + V D – Vin
D = --------------------------------------------Vout + V D – V SW
The average input current depends directly to the output
current when the internal switch is off.
Iout
Iin avg = ------------1–D
Inductor
For calculating the Inductor we should consider the losses
of the internal switch and winding resistance of the inductor.
( Vin – V SW – ( Iin avg × rw ) ) × D
L = ---------------------------------------------------------------------------------Iin avg × r × F SW
It is important to look for an inductor rated at least for the
maximum input current.
Iin max
Vin × ( Vout – Vin )
= Iin avg + ------------------------------------------------2 × L × F SW × Vout
Input Capacitor
The input capacitor should handle at least the following
RMS current.
CSG = A CSA × R Sense
R Comp × 5 × G M × Iout × L
Cout = -------------------------------------------------------------------( 1 – D ) × Vout × CSG
The output voltage ripple (ΔVOUT) depends on the ESR of
the Output capacitor, for a low output voltage ripple it is
recommended to use Ceramic capacitors that usually have
very low ESR. Since ceramic capacitor are expensive,
Electrolytic or Tantalum capacitors can be mixed with
ceramic capacitors to have a cheaper solution.
Vout × ΔVout × F SW × L
ESR Cout = --------------------------------------------------------------Vout × ( 1 – D )
The output capacitor should handle at least the following
RMS current.
Network Compensation
Since this Boost converter is current controlled, Type II
compensation is needed.
D Irms Cout = Iout × -----------1–D
I order to calculate the Network Compensation, first we
need to calculate all Boost Converter components.
For this type of compensations we need to push out the
Right Half Plane Zero to higher frequencies where it can’t
affect the overall loop significantly.
2
Vout × ( 1 – D )
f RHPZ = ---------------------------------------Iout × 2 × π × L
The Crossover frequency must be set much lower than the
location of the Right half plane zero
Vin × ( Vout – Vin )
Irms Cin = ⎛⎝ -------------------------------------------------⎞⎠ × 0.3
2 × L × F SW × Vout
Output Capacitor
For the output capacitor selection the internal current
sense gain (CSG) and the Transconductance should be
taken in consideration.
The CSG is the internal RSENSE times the current sense
amplifier gain (ACSA).
f RHPZ
f Cross = --------------5
Since our system has a fixed Slope compensation set by
RSLOPE, RCOMP should be fixed for all configurations.
R Comp = 5.6kohm
CCOMP1 and CCOMP2 should be calculated as follows:
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
55
COMPONENTS CALCULATION
3
2
C Comp1 = -------------------------------------------------------f Cross × R Comp × π × 2
33 ×10
R SLOPE = ----------------------------V SLOPE × 5
GM
C Comp2 = --------------------------6.28 × F SW
In order to improve the transient response of the boost, on
the 34844A, a resistor divider has been implemented from
the PWM pin to ground with a connection to the
compensation network. This configuration should inject a
1.0 V signal to the COMP pin and the Thevenin-equivalent
resistance of the divider is close to RCOMP, i.e. RCOMP = 6.8 k
and RPCOMP= 27 k for a 5.0 V PWM signal.
PWM
CCOMP1
COMP PIN
RPCOMP
CCOMP2
RCOMP
Slope Compensation
Slope Compensation can be expressed either in terms of
Ampers/Second or as Volts/Second, through the use of the
transfer resistance.
The following formula express the Slope Compensation in
terms of V/μs:
( Vout – Vin ) × CSG
V SLOPE = ---------------------------------------------------L×2
Variable Definition
D= Boost Duty Cycle
VOUT= Output Voltage
VD= Diode Forward Voltage
VIN= Input Voltage
VSW= VDROP of Internal Switch
ΔVOUT= Output Voltage Ripple Ratio
IINAVG= Average Input Current
IOUT= Output Current
r=Input Current Ratio
IINMAX= Maximum input current
IRMSCIN= RMS current for Input Capacitor
IRMSCOUT= RMS current for Output Capacitor
L= Inductor
RW= Inductor winding DC Resistance
fSW= Boost Switching Frequency
CSG= Current Sense Gain = 0.2 V/A
ACSA= Current Sense Amplifier Gain = 9
RSENSE= Current Sense Resistor = 22mohm
COUT= Output Capacitor
RCOMP= Compensation Resistor
GM= OTA Transconductance
ESRCOUT= ESR of Output Capacitor
fRHPZ= Right Half Plane Zero Frequency
fCROSS= Crossover Frequency
CCOMP1= Compensation Capacitor
CCOMP2= Shunt Compensation Capacitor
VSLOPE= Slope Compensation (V/μs)
RSLOPE= External Resistor for Slope Compensation
Where “L” is in μH
In order to have this slope compensation, the following
resistor should be set.
34844
56
Analog Integrated Circuit Device Data
Freescale Semiconductor
LAYOUT GUIDELINES
LAYOUT GUIDELINES
RECOMMENDED STACK-UP
SWITCHING NODE (SWA & SWB)
The following table shows the recommended layer stackup for the signals to have good shielding and Thermal
Dissipation.
The components associated to this node must be placed
as close as possible to each other to keep the switching loop
small enough so that it does not contaminate other signals.
However, care must be taken to ensure the copper traces
used to connect these components together on this node are
capable to handle the necessary current and voltage.
As a reference, a 10 mils trace with a thickness of 1.0 oz.
of copper is capable of handling one ampere.
Traces for connecting the inductor, input and output caps
should be as wide and short as possible to avoid adding
inductance or resistance to the loop. The placement of these
components should be selected far away from sensitive
signals like compensation, feedback and internal regulators
to avoid power noise coupling.
Table 16. Layer Stacking Recommendations
Stack-Up
Layer 1 (Top)
Signal
Layer 2 (Inner 1)
Ground
Layer 3(Inner 2)
Signal
Layer 4 (Bottom)
Ground
DECOUPLING CAPS
It is recommended to place decoupling caps of 100 pf at
the beginning and at the end of any power signal traces to
filter high frequency noise.
Decoupling caps of 100 pf should be also placed at the
end of any long trace to cancel antenna effects on it.
These caps should be located as closed as possible to the
point to be decoupled and the connection to GND should be
as short as possible.
SM-BUS/I2C COMMUNICATION AND CLOCK
SIGNALS (SDA, SCK AND CK)
COMPENSATION COMPONENTS
Components related with COMP pin need to be placed as
close as possible to the pin.
FEEDBACK SIGNAL
The trace of the feedback signal (VOUT) should be routed
perpendicularly or at 45° on a different layer to avoid coupling
noise, preferably between ground or power planes.
To avoid contamination of these signals by nearby high
power or high frequency signals, it is a good practice to shield
them with ground planes placed on adjacent layers. Make
sure the ground plane is uniform through the whole signal
trace length.
IInnppuut
Ca
Capp
ut C
S
Sw
wiititcchhiin
ingg N
Noodde
de
DO
Signal
On State
FFe
dbaac
ackk
Feeeddb
S
Si
Siggn
gnaall
C
Coom
mppeen
enssa
saattiiioonn
Off State
Signal
O
Caapp
Ouuttppuutt C
Ground Planes
Ground Plane
Figure 32. Recommended shielding for critical signals.
These signals shall not run parallel to power signals or
other clock signals in the same routing layer. If they have to
cross or to be routed close to a power signal, it is a good
practice to trace them perpendicularly or at 45° on a different
layer to avoid coupling noise.
Figure 33. Feedback Signal Tracing
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
57
PACKAGING
PACKAGE DIMENSIONS
PACKAGING
PACKAGE DIMENSIONS
For the most current package revision, visit www.freescale.com and perform a keyword search using the “98A” listed below.
EP SUFFIX
32-PIN
98ASA10800D
REVISION O
34844
58
Analog Integrated Circuit Device Data
Freescale Semiconductor
PACKAGING
PACKAGE DIMENSIONS
EP SUFFIX
32-PIN
98ASA10800D
REVISION O
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
59
PACKAGING
PACKAGE DIMENSIONS
EP SUFFIX
32-PIN
98ASA10800D
REVISION O
34844
60
Analog Integrated Circuit Device Data
Freescale Semiconductor
REVISION HISTORY
REVISION HISTORY
REVISION
DATE
DESCRIPTION OF CHANGES
3.0
11/2008
• Initial Release
4.0
3/2009
•
•
•
•
5.0
5/2009
• Corrected Compensation Components paragraph on page 32.
6.0
9/2009
• Added Part Number MC34844AEP/R2.
7.0
3/2010
8.0
7/2010
9.0
3/2012
• Combined Complete Data sheet for Part Numbers MC34844 and MC34844A to this data
sheet.
• Removed OVP=4h, OVP=3h and OVP=2h rows from Table 11.
• PWM and CK Frequency range changed in Electrical Characteristics table.
• Added resistor between VDC1 and VDC3 on the application drawings. Added to notes
for VDC3 on pages 9, 14, 37, and 42.
Added PWM Pin to Maximum Voltages in Maximum Rating Table.
Added Disabling LED Channels
Rewrote Fail Pin section
Added I2C Bus Specification
34844
Analog Integrated Circuit Device Data
Freescale Semiconductor
61
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MC34844
Rev. 9.0
3/2012
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