LM3528 High Efficiency, Multi Display LED Driver with 128 Exponential... and Integrated OLED Power Supply in a 1.2mm × 1.6mm...

LM3528 High Efficiency, Multi Display LED Driver with 128 Exponential... and Integrated OLED Power Supply in a 1.2mm × 1.6mm...
LM3528
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SNVS513B – AUGUST 2008 – REVISED MAY 2013
LM3528 High Efficiency, Multi Display LED Driver with 128 Exponential Dimming Steps
and Integrated OLED Power Supply in a 1.2mm × 1.6mm DSBGA Package
Check for Samples: LM3528
FEATURES
APPLICATIONS
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2
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128 Exponential Dimming Steps
Programmable Auto-Dimming Function
Up to 90% Efficient
Low Profile 12 Bump DSBGA Package (1.2mm
x 1.6mm x 0.6mm)
Integrated OLED Display Power Supply and
LED Driver
Programmable Pattern Generator Output for
LED Indicator Function
Drives up to 12 LED’s at 20mA
Drives up to 5 LED’s at 20mA and delivers 18V
at 40mA
1% Accurate Current Matching Between
Strings
Internal Soft-Start Limits Inrush Current
True Shutdown Isolation for LED’s
Wide 2.5V to 5.5V Input Voltage Range
22V Over-Voltage Protection
1.25MHz Fixed Frequency Operation
Dedicated Programmable General Purpose I/O
Active Low Hardware Reset
10 PH
2.7V to 5.5V
IN
The LM3528 current mode boost converter offers two
separate outputs. The first output (MAIN) is a
constant current sink for driving series white LED’s.
The second output (SUB/FB) is configurable as a
constant current sink for series white LED bias, or as
a feedback pin to set a constant output voltage for
powering OLED panels.
As a dual output white LED bias supply, the LM3528
adaptively regulates the supply voltage of the LED
strings to maximize efficiency and insure the current
sinks remain in regulation. The maximum current per
output is set via a single external low power resistor.
An I2C compatible interface allows for independent
adjustment of the LED current in either output from 0
to max current in 128 exponential steps. When
configured as a white LED + OLED bias supply the
LM3528 can independently and simultaneously drive
a string of up to 6 white LED’s and deliver a constant
output voltage of up to 21V for OLED panels.
SW
OVP
C
1 PF
4.4mm
VIO
DESCRIPTION
20 mA per string
CIN
1 PF
10 k:
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Dual Display LCD Backlighting for Portable
Applications
Large Format LCD Backlighting
OLED Panel Power Supply
Display Backlighting with Indicator Light
LM3528
10 k:
MAIN
SCL
SDA
SUB/FB
HWEN/PGEN/
GPIO
GPIO
Current
Limiting
Resistor
SET
GND
RSET
1 M:
12.1 k:
6.5mm
Indicator
LED
Dual White LED Bias Supply with Indicator LED
Figure 1. Typical Application Circuit
Figure 2. Typical PCB Layout
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2013, Texas Instruments Incorporated
LM3528
SNVS513B – AUGUST 2008 – REVISED MAY 2013
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This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
DESCRIPTION (CONTINUED)
Output over-voltage protection shuts down the device if VOUT rises above 22V allowing for the use of small sized
low voltage output capacitors. Other features include a dedicated general purpose I/O (GPIO) and a multifunction pin (HWEN/PGEN/GPIO) which can be configured as a 32 bit pattern generator, a hardware enable
input, or as a GPIO. When configured as a pattern generator, an arbitrary pattern is programmed via the I2C
compatible interface and output at HWEN/PGEN/GPIO for indicator LED flashing or for external logic control.
The LM3528 is offered in a tiny 12-bump DSBGA package and operates over the -40°C to +85°C temperature
range.
Connection Diagram
Top View
A1
A2
A3
B1
B2
B3
C1
C2
C3
D1
D2
D3
Figure 3. 12-Bump (1.215mm × 1.615mm × 0.6mm) YFQ0012
PIN DESCRIPTIONS
Pin
Name
A1
OVP
Over-Voltage Protection Sense Connection. Connect OVP to the positive terminal of the output
capacitor.
A2
MAIN
Main Current Sink Input.
A3
SUB/FB
Secondary Current Sink Input or 1.21V Feedback Connection for Constant Voltage Output.
B1
GPIO1
Programmable General Purpose I/O.
B2
SCL
Serial Clock Input
B3
SET
LED Current Setting Connection. Connect a resistor from SET to GND to set the maximum LED
current into MAIN or SUB/FB (when in LED mode), where ILED_MAX = 192×1.244V/RSET.
C1
Function
HWEN/PGEN/GPI Active High Hardware Enable Input. Programmable Pattern Generator Output, and Programmable
O
General Purpose I/O.
C2
SDA
C3
IN
Serial Data Input/Output
D1
VIO
Logic Voltage Level Input
D2
SW
Drain Connection for Internal NMOS Switch
D3
GND
Ground
Input Voltage Connection. Connect IN to the input supply, and bypass to GND with a 1µF ceramic
capacitor.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
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Absolute Maximum Ratings
(1) (2) (3)
−0.3V to 6V
VIN
VSW, VOVP,
−0.3V to 25V
VSUB/FB, VMAIN
−0.3V to 23V
−0.3V to 6V
VSCL, VSDA, VRESET\GPIO, VIO , VSET
Continuous Power Dissipation
Internally Limited
Junction Temperature (TJ-MAX)
+150°C
Storage Temperature Range
-65°C to +150°C
Maximum Lead Temperature (Soldering, 10s) (4)
+300°C
ESD Rating (5)
Human Body Model
(1)
(2)
(3)
(4)
(5)
2.5kV
Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the
device is intended to be functional, but device parameter specifications may not be ensured. For ensured specifications and test
conditions, see the Electrical Characteristics.
If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
All voltages are with respect to the potential at the GND pin.
For detailed soldering specifications and information, please refer to Texas Instruments Application Note 1112: DSBGA Wafer LEvel
Chip Scale Package (SNVA009).
The human body model is a 100pF capacitor discharged through 1.5kΩ resistor into each pin. (MIL-STD-883 3015.7).
Operating Ratings
(1) (2)
VIN
2.5V to 5.5V
VSW, VOVP,
0V to 23V
VSUB/FB, VMAIN
0V to 21V
Junction Temperature Range (TJ) (3)
-40°C to +110°C
Ambient Temperature Range (TA) (4)
-40°C to +85°C
(1)
(2)
(3)
(4)
Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the
device is intended to be functional, but device parameter specifications may not be ensured. For ensured specifications and test
conditions, see the Electrical Characteristics.
All voltages are with respect to the potential at the GND pin.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=+150°C (typ.) and
disengages at TJ=+140°C (typ.).
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP
= +105°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of
the part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Thermal Properties
Junction to Ambient Thermal Resistance (θJA) (1)
(1)
68°C/W
Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 114.3mm x 76.2mm x 1.6mm. The ground
plane on the board is 113mm x 75mm. Thickness of copper layers are 71.5µm/35µm/35µm/71.5µm (2oz/1oz/1oz/2oz). Ambient
temperature in simulation is 22°C, still air. Power dissipation is 1W. For more information on these topics, please refer to Texas
Instruments Application Note 1112 SNVA009, and JEDEC Standard JESD51-7.
Electrical Characteristics
Specifications in standard type face are for TA = 25°C and those in boldface type apply over the Operating Temperature
Range of TA = −40°C to +85°C. Unless otherwise specified VIN = 3.6V, VIO = 1.8V, VRESET/GPIO = VIN, VSUB/FB = VMAIN = 0.5V,
R = 12.0kΩ, OLED = ‘0’, ENM = ENS = ‘1’, BSUB = BMAIN = Full Scale. (1) (2)
SET
Symbol
ILED
(1)
(2)
Parameter
Conditions
Output Current Regulation
MAIN or SUB/FB Enabled
UNI = ‘0’, or ‘1’,
2.5V < VIN < 5.5V
Maximum Current Per
Current Sink
RSET = 8.0kΩ
Min
18.5
Typ
Max
20
22
30
Units
mA
All voltages are with respect to the potential at the GND pin.
Min and Max limits are ensured by design, test, or statistical analysis. Typical (Typ) numbers are not ensured, but represent the most
likely norm.
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Electrical Characteristics (continued)
Specifications in standard type face are for TA = 25°C and those in boldface type apply over the Operating Temperature
Range of TA = −40°C to +85°C. Unless otherwise specified VIN = 3.6V, VIO = 1.8V, VRESET/GPIO = VIN, VSUB/FB = VMAIN = 0.5V,
R = 12.0kΩ, OLED = ‘0’, ENM = ENS = ‘1’, BSUB = BMAIN = Full Scale.(1) (2)
SET
Symbol
Parameter
Conditions
Min
Typ
Max
Units
0.15
1
%
ILED-MATCH
IMAIN to ISUB/FB Current
Matching
UNI = ‘1’,
2.5V < VIN < 5.5V
VSET
SET Pin Voltage
3.0V < VIN < 5V
ILED/ISET
ILED Current to ISET Current
Ratio
192
VREG_CS
Regulated Current Sink
Headroom Voltage
500
VREG_OLED
VSUB/FB Regulation Voltage in 2.5V < VIN < 5.5V, OLED =
OLED Mode
‘1’
VHR
Current Sink Minimum
Headroom Voltage
RDSON
NMOS Switch On Resistance ISW = 100mA
ICL
NMOS Switch Current Limit
2.5V < VIN < 5.5V
645
770
900
VOVP
Output Over-Voltage
Protection
ON Threshold,
2.5V < VIN < 5.5V
20.6
22
23
OFF Threshold,
2.7V < VIN < 5.5V
19.25
20.6
21.5
1.0
1.27
1.4
(3)
1.244
1.170
ILED = 95% of nominal
1.21
V
mV
1.237
300
V
mV
Ω
0.43
mA
V
fSW
Switching Frequency
DMAX
Maximum Duty Cycle
90
%
DMIN
Minimum Duty Cycle
10
%
IQ
Quiescent Current, Device
Not Switching
ISHDN
Shutdown Current
MHz
VMAIN and VSUB/FB >
VREG_CS,
BSUB = BMAIN = 0x00, 2.5V
< VIN < 5.5V
350
VSUB/FB > VREG_OLED,
OLED=’1’, ENM=ENS=’0’,
RSET Open,
2.5V < VIN < 5.5V
250
260
ENM = ENS = OLED = '0',
2.5V < VIN < 5.5V
1.8
3
µA
0.5
V
390
µA
HWEN/PGEN/GPIO, GPIO1 Pin Voltage Specifications
VIL
Input Logic Low
2.5V < VIN <5.5V, MODE bit
=0
VIH
Input Logic High
2.5V < VIN < 5.5V, MODE bit
=0
VOL
Output Logic Low
ILOAD=3mA, MODE bit = 1
1.1
V
400
mV
VIN
V
0.36×VIO
V
400
mV
I2C Compatible Voltage Specifications (SCL, SDA, VIO)
VIO
Serial Bus Voltage Level
2.5V < VIN < 5.5V
VIL
Input Logic Low
2.5V < VIN < 5.5V
VIH
Input Logic High
2.5V < VIN < 5.5V
VOL
Output Logic Low
ILOAD = 3mA
(4)
I2C Compatible Timing Specifications (SCL, SDA, VIO, see Figure 4)
1.7
0.7×VIO
V
(5) (4)
t1
SCL Clock Period
2.5
µs
t2
Data In Setup Time to SCL
High
100
ns
t3
Data Out Stable After SCL
Low
0
ns
(3)
(4)
(5)
4
The matching specification between MAIN and SUB is calculated as 100 × ((IMAIN or ISUB) - IAVE) / IAVE. This simplifies out to be 100 ×
(IMAIN - ISUB)/(IMAIN + ISUB).
SCL and SDA signals are referenced to VIO and GND for minimum VIO voltage testing. VIO limits indicate the minimum voltage at VIO
at which the part is operational.
SCL and SDA must be glitch-free in order for proper brightness control to be realized.
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Electrical Characteristics (continued)
Specifications in standard type face are for TA = 25°C and those in boldface type apply over the Operating Temperature
Range of TA = −40°C to +85°C. Unless otherwise specified VIN = 3.6V, VIO = 1.8V, VRESET/GPIO = VIN, VSUB/FB = VMAIN = 0.5V,
R = 12.0kΩ, OLED = ‘0’, ENM = ENS = ‘1’, BSUB = BMAIN = Full Scale.(1) (2)
SET
Symbol
t4
t5
Parameter
Conditions
Min
Typ
Max
Units
SDA Low Setup Time to SCL
Low (Start)
100
ns
SDA High Hold Time After
SCL High (Stop)
100
ns
Timing Diagram
t1
t5
t4
t2
t3
Figure 4. I2C Timing
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Typical Performance Characteristics
VIN = 3.6V, LEDs are Nichia (NSSW008C), COUT = 1µF (LED Mode), COUT = 2.2µF (OLED Mode), CIN = 1µF, L = TDK
VLF4012AT-100MR79, (RL = 0.3Ω), RSET = 12.1kΩ, UNI = '1', ILED = ISUB + IMAIN, TA = +25°C unless otherwise specified.
6
2x6 LED Efficiency
vs
ILED
(2 Strings of 6LEDs)
2x5 LED Efficiency
vs
ILED
(2 Strings of 5LEDs)
Figure 5.
Figure 6.
2x4 LED Efficiency
vs
ILED
(2 Strings of 4LEDs)
2x3 LED Efficiency
vs
ILED
(2 Strings of 3LEDs)
Figure 7.
Figure 8.
2x2 LED Efficiency
vs
ILED
(2 Strings of 2LEDs)
LED Efficiency
vs
VIN
(L = TDK VLF3012AT-100MR92, RL = 0.36Ω, ISUB + IMAIN =
40mA)
Figure 9.
Figure 10.
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Nichia (NSSW008C), COUT = 1µF (LED Mode), COUT = 2.2µF (OLED Mode), CIN = 1µF, L = TDK
VLF4012AT-100MR79, (RL = 0.3Ω), RSET = 12.1kΩ, UNI = '1', ILED = ISUB + IMAIN, TA = +25°C unless otherwise specified.
18V OLED Efficiency
vs
IOUT
12V OLED Efficiency
vs
IOUT
Figure 11.
Figure 12.
LED Line Regulation
(UNI = '0')
OLED Line Regulation
IOLED = 60mA
Figure 13.
Figure 14.
OLED Line Regulation
IOLED = 60mA
OLED Load Regulation
VOLED = 18V
Figure 15.
Figure 16.
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Nichia (NSSW008C), COUT = 1µF (LED Mode), COUT = 2.2µF (OLED Mode), CIN = 1µF, L = TDK
VLF4012AT-100MR79, (RL = 0.3Ω), RSET = 12.1kΩ, UNI = '1', ILED = ISUB + IMAIN, TA = +25°C unless otherwise specified.
8
OLED Load Regulation
VOLED = 12V
Peak Current Limit
vs.
VIN
Figure 17.
Figure 18.
Over Voltage Limit
vs.
VIN
Switch On-Resistance
vs.
VIN
Figure 19.
Figure 20.
Switching Frequency
vs.
VIN
Maximum Duty Cycle
vs.
VIN
Figure 21.
Figure 22.
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Nichia (NSSW008C), COUT = 1µF (LED Mode), COUT = 2.2µF (OLED Mode), CIN = 1µF, L = TDK
VLF4012AT-100MR79, (RL = 0.3Ω), RSET = 12.1kΩ, UNI = '1', ILED = ISUB + IMAIN, TA = +25°C unless otherwise specified.
(1)
Shutdown Current
vs.
VIN
Switching Supply Current
vs.
VIN
Figure 23.
Figure 24.
LED Current Matching
vs.
CODE (1)
(UNI = '1', RSET = 12kΩ, TA = -40°C to +85°C)
LED Current Accuracy
vs
CODE
(RSET = 12kΩ±0.05%)
Figure 25.
Figure 26.
LED Current
vs
CODE
(IMAIN, ISUB, IIDEAL, RSET = 12kΩ±0.05%)
ILED
vs
Current Source Headroom Voltage
(VIN = 3V, UNI = '0')
Figure 27.
Figure 28.
The matching specification between MAIN and SUB is calculated as 100 × ((IMAIN or ISUB) - IAVE) / IAVE. This simplifies out to be 100 ×
(IMAIN - ISUB)/(IMAIN + ISUB).
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Nichia (NSSW008C), COUT = 1µF (LED Mode), COUT = 2.2µF (OLED Mode), CIN = 1µF, L = TDK
VLF4012AT-100MR79, (RL = 0.3Ω), RSET = 12.1kΩ, UNI = '1', ILED = ISUB + IMAIN, TA = +25°C unless otherwise specified.
Start-Up Waveform (LED Mode)
(2 × 5 LEDs, 20mA per string)
Start-Up Waveform (OLED Mode)
(VOUT = 18V, IOUT = 60mA)
Channel 2: SDA (5V/div)
Channel 1: VOUT (10V/div)
Channel 3: ILED (20mA/div)
Channel 4: IIN (200mA/div)
Time Base: 400µs/div
Channel 1: SDA (5V/div)
Channel 2: VOUT (10V/div)
Channel 3: IOUT (20mA/div)
Channel 4: IIN (200mA/div)
Time Base: 400µs/div
Figure 29.
Figure 30.
Load Step (OLED Mode)
(VOUT = 18V, COUT = 2.2µF)
Line Step (LED Mode)
(2 × 5 LEDs, 20mA per String, COUT = 1µF, VIN from 3V to
3.6V)
Channel 3: ISUB (5mA/div)
Channel 4: IMAIN (5mA/div)
Channel 2: VIN (AC Coupled, 500mV/div)
Time Base: 100µs/div
Figure 32.
Channel 2: VOUT (AC Coupled, 500mV/div)
Channel 3: IOUT (20mA/div)
Time Base: 200µs/div
Figure 31.
Line Step (OLED Mode)
(VOUT = 18V, COUT = 2.2µF, VIN from 3V to 3.6V)
Channel 2: VOUT (AC Coupled, 100mV/div)
Channel 3: VIN (AC Coupled, 500mV/div)
Time Base: 200µs/div
HWEN Functionality
Channel 4: ISUB (20mA/div)
Channel 3: IMAIN (20mA/div)
Channel 2: HWEN (5V/div)
Time Base: 200ns/div
Figure 33.
10
Figure 34.
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Typical Performance Characteristics (continued)
VIN = 3.6V, LEDs are Nichia (NSSW008C), COUT = 1µF (LED Mode), COUT = 2.2µF (OLED Mode), CIN = 1µF, L = TDK
VLF4012AT-100MR79, (RL = 0.3Ω), RSET = 12.1kΩ, UNI = '1', ILED = ISUB + IMAIN, TA = +25°C unless otherwise specified.
GPIO1 Functionality
(GPIO1 Configured as OUTPUT, fSCL = 360kHz)
Channel 2: GPIO (2V/div)
Channel 1: SCL (5V/div)
Channel 1:SDA (5V/div)
Time Base: 40µs/div
Ramp Rate Functionality
(RMP1, RMP0 = '11')
Channel 1:SDA (2V/div)
Channel 4: ISUB (10mA/div)
Channel 3: ISUB (10mA/div)
Time Base: 400ms/div
Figure 35.
Figure 36.
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BLOCK DIAGRAM
IN
SW
OVP
S0
500 mV
S1
1.2V
MUX
SOFT START
ERROR
AMP
Thermal
shutdown
Light
Load
OVP
OLED
+
-
R
R
R
R
RZ
0.5:
S
GPIO
R
CC
Osc/
Ramp
Driver
Over
Current
Protection
HWEN/PGEN/GPIO
¦
gm
MAIN
S0
IMAIN
MUX
MIN
S1
VIO
OLED
SDA
1.244V
1.244V
ILED_MAX =
RSET
SET
SUB/FB
5 BIT
CONTROL
I2C/
CONTROL
SCL
ISUB/FB
5 BIT
CONTROL
192
GND
Figure 37. LM3528 Block Diagram
OPERATION DESCRIPTION
The LM3528 Current Mode PWM boost converter operates from a 2.7V to 5.5V input and provides two regulated
outputs for White LED and OLED display biasing. The first output, MAIN, provides a constant current of up to
30mA to bias up to 6 series white LED’s. The second output, SUB/FB, can be configured as a current source for
up to 6 series white LED’s at up to 30mA, or as a feedback voltage pin to regulate a constant output voltage of
up to 21V. When both MAIN and SUB/FB are configured for white LED bias the current for each LED string is
controlled independently or in unison via an I2C-compatible interface. When MAIN is configured for white LED
bias and SUB/FB is configured as a feedback voltage pin, the current into MAIN is controlled via the I2Ccompatible interface and SUB/FB becomes the middle tap of a resistive divider used to regulate the output
voltage of the boost converter.
The core of the LM3528 is a Current Mode Boost converter. Operation is as follows. At the start of each
switching cycle the internal oscillator sets the PWM converter. The converter turns the NMOS switch on, allowing
the inductor current to ramp while the output capacitor supplies power to the white LED’s and/or OLED panel.
The error signal at the output of the error amplifier is compared against the sensed inductor current. When the
sensed inductor current equals the error signal, or when the maximum duty cycle is reached, the NMOS switch
turns off causing the external Schottky diode to pick up the inductor current. This allows the inductor current to
ramp down causing its stored energy to charge the output capacitor and supply power to the load. At the end of
the clock period the PWM controller is again set and the process repeats itself.
12
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Adaptive Regulation
When biasing dual white led strings (White LED mode) the LM3528 maximizes efficiency by adaptively regulating
the output voltage. In this configuration the 500mV reference is connected to the non-inverting input of the error
amplifier via mux S2 (see Figure 37). The lowest of either VMAIN or VSUB/FB is then applied to the inverting input of
the error amplifier via mux S1. This ensures that VMAIN and VSUB/FB are at least 500mV, thus providing enough
voltage headroom at the input to the current sinks for proper current regulation.
In the instance when there are unequal numbers of LEDs or unequal currents from string to string, the string with
the highest voltage will be the regulation point.
Unison/Non-Unison Mode
Within White LED mode there are two separate modes of operation, Unison and Non-Unison. Non-Unison mode
provides for independent current regulation, while Unison mode gives up independent regulation for more
accurate matching between LED strings. When in Non-Unison mode the LED currents IMAIN and ISUB/FB are
independently controlled via registers BMAIN and BSUB respectively (see Brightness Registers (BMAIN and
BSUB) section). When in Unison mode BSUB is disabled and both IMAIN and ISUB/FB are controlled via BMAIN
only.
Start-Up
The LM3528 features an internal soft-start, preventing large inrush currents during start-up that can cause
excessive voltage ripple on the input. For the typical application circuits when the device is brought out of
shutdown the average input current ramps from zero to 450mA in approximately 1.2ms. See Start Up Plots in the
Typical Performance Characteristics.
OLED Mode
When the LM3528 is configured for a single White LED bias + OLED display bias (OLED mode), the noninverting input of the error amplifier is connected to the internal 1.21V reference via MUX S2. MUX S1 switches
SUB/FB to the inverting input of the error amplifier while disconnecting the internal current sink at SUB/FB. The
voltage at MAIN is not regulated in OLED mode so when the application requires white LED + OLED panel
biasing, ensure that at least 300mV of headroom is maintained at MAIN to ensure proper regulation of IMAIN. (see
the Typical Performance Characteristics for a plot of ILED vs Current Source Headroom Voltage)
Peak Current Limit
The LM3528’s boost converter has a peak current limit for the internal power switch of 770mA typical (650mA
minimum). When the peak switch current reaches the current limit the duty cycle is terminated resulting in a limit
on the maximum output current and thus the maximum output power the LM3528 can deliver. Calculate the
maximum LED current as a function of VIN, VOUT, L and IPEAK as:
(IPEAK
IOUT_MAX =
where
'IL =
'IL) u K u VIN
VOUT
VIN u (VOUT
VIN)
2 u fSW u L u VOUT
(1)
ƒSW = 1.27MHz. Typical values for efficiency and IPEAK can be found in the efficiency and IPEAK curves in the
Typical Performance Characteristics.
Over Voltage Protection
The LM3528's output voltage (VOUT) is limited on the high end by the Output Over-Voltage Protection Threshold
(VOVP) of 21.2V (min). In White LED mode during output open circuit conditions the output voltage will rise to the
over voltage protection threshold. When this happens the controller will stop switching causing VOUT to droop.
When the output voltage drops below 19.7V (min) the device will resume switching. If the device remains in an
over voltage condition the LM3528 will repeat the cycle causing the output to cycle between the high and low
OVP thresholds. See waveform for OVP condition in the Typical Performance Characteristics.
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Output Current Accuracy and Current Matching
The LM3528 provides both precise current accuracy (% error from ideal value) and accurate current matching
between the MAIN and SUB/FB current sinks. Two modes of operation affect the current matching between IMAIN
and ISUB/FB. The first mode (Non-Unison mode) is set by writing a 0 to bit 2 of the General Purpose register (UNI
bit). Non-Unison mode allows for independent programming of IMAIN and ISUB/FB via registers BMAIN and BSUB
respectively. In this mode typical matching between current sinks is 1%.
Writing a 1 to UNI configures the device for Unison mode. In Unison mode, BSUB is disabled and IMAIN and
ISUB/FB are both controlled via register BMAIN. In this mode typical matching is 0.15%.
Light Load Operation
The LM3528 boost converter operates in three modes; continuous conduction, discontinuous conduction, and
skip mode operation. Under heavy loads when the inductor current does not reach zero before the end of the
switching period the device switches at a constant frequency. As the output current decreases and the inductor
current reaches zero before the end of the switching cycle, the device operates in discontinuous conduction. At
very light loads the LM3528 will enter skip mode operation causing the switching period to lengthen and the
device to only switch as required to maintain regulation at the output.
Hardware Enable/Pattern Generator/General Purpose I/O (HWEN/PGEN/GPIO)
HWEN/PGEN/GPIO can be configured for three different modes of operation; Hardware Enable, Pattern
Generation, and General Purpose I/O. Register HPG at address 0x80 controls the functionality of this pin (see
Table 6).
Hardware Enable (HWEN)
On initial power-up HWEN/PGEN/GPIO defaults to the Hardware Enable (HWEN) state. In this mode
HWEN/PGEN/GPIO is an active high open-drain input enable to the device. When in HWEN mode
HWEN/PGEN/GPIO must be pulled up to at least 0.7 × VIO to enable the device. In HWEN mode pulling
HWEN/PGEN/GPIO below 0.36 × VIO will shutdown the LM3528, resetting all registers, and forcing MAIN,
SUB/FB, and SW high impedance. Bit 0 of the HPG register controls the HWEN function. Writing a ‘0’ to this bit
enables the HWEN mode. Writing a ‘1’ to this bit disables the HWEN mode and allows selection between the
other two modes.
Pattern Generator (PGEN)
With bit 0 of the HPG register set to 1, HWEN/PGEN/GPIO can be programmed as an open drain Pattern
Generator Output (PGEN). In PGEN mode a 32 bit pattern is output at HWEN/PGEN/GPIO. This pattern can be
programmed to repeat itself at 4 different frequencies and 6 different duty cycles. The arbitrary pattern is
programmed into four 8 bit registers; PGEN0 (address 0x90), PGEN1 (address 0x91), PGEN2 (address 0x92),
and PGEN3 (address 0x93) (see Figure 47 - Figure 50). Figure 51 details an example of a 32 bit pattern at a
specific programmed duty cycle and frequency. A ‘1’ written to the PGEN_ registers forces HWEN/PGEN/GPIO
low. A ‘0’ causes HWEN/PGEN/GPIO to go open drain.
Bits <5:3> in the HPG register have three functions; GPIO enable, duty cycle select, and pattern latch. Any
combination of these bits other than ‘000’ or ’111’ puts HWEN/PGEN/GPIO into PGEN mode at the specified
duty cycle shown in Table 6. Writing a ‘111’ to bits <5:3> latches the 32 bit pattern programmed into the 4 pattern
generator registers PGEN0, PGEN1, PGEN2, PGEN3 into the internal shift register. When bits <5:3> = ‘000’ the
PGEN mode is off and HWEN/PGEN/GPIO is configured as a GPIO.
Bits <7:6> of the HPG register control the pattern frequency. See Table 6 for the detailed breakdown of each
available frequency. Figure 51 details the pattern programming and Figure 52 shows the pattern output at
HWEN/PGEN/GPIO.
General Purpose I/O (GPIO1)
With bits <5:3> and bit 0 of the HPG register all set to ‘0’ HWEN/PGEN/GPIO functions as an open drain
General Purpose I/O. In this mode, bit 1 of the HPG register controls the logic direction (Input or Output) and bit
2 holds the logic data. With bit 1 set to ‘0’ HWEN/PGEN/GPIO is configured as an output. In this mode a ‘0’
written to bit 2 forces HWEN/PGEN/GPIO to logic low. Likewise, a ‘1’ written to bit 2 will force
HWEN/PGEN/GPIO open drain. When bit 1 is set to ‘1’ HWEN/PGEN/GPIO is configured as a logic input. In this
14
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mode when HWEN/PGEN/GPIO is externally pulled low a ‘0’ is written to bit 2 of the HPG register. Likewise,
when HWEN/PGEN/GPIO is externally pulled high a ‘1’ is written to bit 2 of the HPG register. Table 6 and
Figure 45 detail the bit functions of the HPG register and their power-on-reset values. Note that the logic output
levels for the GPIO function of this pin are inverted compared to the PGEN functions. For example, a 1 written to
the PGEN registers cause the HWEN/PGEN/GPIO pin to pull low while a 1 written to bit 2 of the HPG register
causes the pin to go open drain.
General Purpose I/O (GPIO0)
The GPIO pin is a dedicated General Purpose I/O (open drain) and is controlled via the GPIO register at address
0x81. Bit 1 holds the logic data while bit 0 controls the logic direction (Input or Output). Bits <7:2> are un-used
and will always read back as logic '1'. With bit 0 set to ‘0’ GPIO is configured as an output. In this mode a ‘0’
written to bit 1 forces GPIO to a logic low. Likewise, a ‘1’ written to bit 1 will force GPIO to logic high. When bit 0
is set to ‘1’ GPIO is configured as a logic input. In this mode when GPIO is externally pulled low a ‘0’ is written to
bit 1 of the GPIO register. Likewise, when GPIO is externally pulled high a ‘1’ is written to bit 2 of the HPG
register. Table 8 and Figure 46 detail the bit functions and power-on-reset values of GPIO.
During an initial GPIO write two I2C sequences (Slave I.D, Register Address, Register Data) are required to
change the state of the GPIO pin. The first write configures the GPIO pin as an output. The second write will
change the state of the GPIO output to the desired logic '1' or '0'.
Thermal Shutdown
The LM3528 offers a thermal shutdown protection. When the die temperature reaches +140°C the device will
shutdown and not turn on again until the die temperature falls below +120°C.
I2C Compatible Interface
The LM3528 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning
and the end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL
is HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C
master always generates START and STOP conditions. The I2C bus is considered busy after a START condition
and free after a STOP condition. During data transmission, the I2C master can generate repeated START
conditions. A START and a repeated START conditions are equivalent function-wise. The data on SDA must be
stable during the HIGH period of the clock signal (SCL). In other words, the state of SDA can only be changed
when SCL is LOW.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 38. Start and Stop Sequences
I2C Compatible Address
The chip address for the LM3528 is 0110110 (36h). After the START condition, the I2C master sends the 7-bit
chip address followed by a read or write bit (R/W). R/W= 0 indicates a WRITE and R/W = 1 indicates a READ.
The second byte following the chip address selects the register address to which the data will be written. The
third byte contains the data for the selected register.
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MSB
0
Bit 7
LSB
1
Bit 6
1
Bit 5
0
Bit 4
1
Bit 3
1
Bit 2
0
Bit 1
R/W
Bit 0
2
I C Slave Address (chip address)
Figure 39. Chip Address
Transferring Data
Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte
of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is
generated by the master. The master releases SDA (HIGH) during the 9th clock pulse. The LM3528 pulls down
SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each byte has
been received. Figure 40 is an example of a write sequence to the General Purpose register of the LM3528.
SCL
SDA
Chip Address (36h)
START
R/W
ACK
Register Address (10h)
ACK
Register Data (06h)
ACK
STOP
Figure 40. Write Sequence to the LM3528
Register Descriptions
There are 4, 8 bit registers within the LM3528 as detailed in Table 1.
Table 1. LM3528 Register Descriptions
Register Name
Hex Address
Power -On-Value
General Purpose (GP)
0x10
0xC0
Brightness Main (BMAIN)
0xA0
0x80
Brightness Sub (BSUB)
0xB0
0x80
HWEN/PGEN/GPIO Control (HPG)
0x80
0XF8
General Purpose I/O Control (GPIO)
0x81
0xFC
Pattern Register 0 (PGEN0)
0x90
0x00
Pattern Register 1 (PGEN1)
0x91
0x00
Pattern Register 2 (PGEN2)
0x92
0x00
Pattern Register 3 (PGEN3)
0x93
0x00
General Purpose Register (GP)
The General Purpose register has four functions. It controls the on/off state of MAIN and SUB/FB, it selects
between Unison or Non-Unison mode, provides for control over the rate of change of the LED current (see
Brightness Rate of Change Description), and selects between White LED and OLED mode. Figure 41 and
Table 2 describes each bit available within the General Purpose Register. Table 3 summarizes the output state
of the LM3528 for the different combinations of General Purpose register settings.
16
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General Purpose Register
Register Address 0x10
MSB
1
Bit 7
1
Bit 6
OLED
Bit 5
RMP1
Bit 4
RMP0
Bit 3
LSB
UNI
Bit 2
ENS
Bit 1
ENM
Bit 0
Figure 41. General Purpose Register Description
Table 2. General Purpose Register Bit Function
Bit
Name
Function
Power-OnValue
0
ENM
Enable MAIN. Writing a 1 to this bit enables the main current sink (MAIN). Writing a 0 to this bit
disables the main current sink and forces MAIN high impedance.
0
1
ENS
Enable SUB/FB. Writing a 1 to this bit enables the secondary current sink (SUB/FB). Writing a 0 to
this bit disables the secondary current sink and forces SUB/FB high impedance.
0
2
UNI
Unison Mode Select. Writing a 1 to this bit disables the BSUB register and causes the contents of
BMAIN to set the current in both the MAIN and SUB/FB current sinks. Writing a 0 to this bit allows the
current into MAIN and SUB/FB to be independently controlled via the BMAIN and BSUB registers
respectively.
0
3
RMP0
0
4
RMP1
Brightness Rate of Change. Bits RMP0 and RMP1 set the rate of change of the LED current into
MAIN and SUB/FB in response to changes in the contents of registers BMAIN and BSUB (see
Brightness Rate of Change Description).
5
OLED
OLED = 0 places the LM3528 in White LED mode. In this mode both the MAIN and SUB/FB current
sinks are active. The boost converter ensures there is at least 500mV at VMAIN and VSUB/FB. OLED =
1 places the LM3528 in OLED mode. In this mode the boost converter regulates VSUB/FB to 1.244V.
VMAIN is unregulated and must be > 400mV for the MAIN current sink to maintain current regulation.
0
6
Don't Care
These are non-functional read only bits. They will always read back as a 1.
1
0
7
Table 3. Operational Truth Table
UNI
OLED
ENM
ENS
Result
X
0
0
0
LM3528 Disabled
1
0
1
X
MAIN and SUB/FB current sinks enabled. Current levels set by contents
of BMAIN.
1
0
0
X
MAIN and SUB/FB Disabled
0
0
0
1
SUB/FB current sink enabled. Current level set by BSUB.
0
0
1
0
MAIN current sink enabled. Current level set by BMAIN.
0
0
1
1
MAIN and SUB/FB current sinks enabled. Current levels set by contents
of BMAIN and BSUB respectively.
X
1
1
X
SUB/FB current sink disabled (SUB/FB configured as a feedback pin).
MAIN current sink enabled current level set by BMAIN.
X
1
0
X
SUB/FB current sink disabled (SUB/FB configured as a feedback pin).
MAIN current sink disabled.
* ENM ,ENS, or OLED high enables analog circuitry.
Brightness Registers (BMAIN and BSUB)
With the UNI bit (General Purpose register) set to 0 (Non-Unison mode) both brightness registers (BMAIN and
BSUB) independently control the LED currents IMAIN and ISUB/FB respectively. BMAIN and BSUB are both 8 bit,
but with only the 7 LSB’s controlling the current. The MSB’s is a don’t care. The LED current control is designed
to approximate an exponentially increasing response of the LED current vs increasing code in either BMAIN or
BSUB (see Figure 44). Program ILED_MAX by connecting a resistor (RSET) from SET to GND, where:
ILED_MAX = 192 u
1.244V
RSET
(2)
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With the UNI bit (General Purpose register) set to 1 (Unison mode), BSUB is disabled and BMAIN sets both IMAIN
and ISUB/FB. This prevents the independent control of IMAIN and ISUB/FB, however matching between current sinks
goes from typically 1%(with UNI = 0) to typically 0.15% (with UNI = 1). Figure 42 and Figure 43 show the register
descriptions for the Brightness MAIN and Brightness SUB registers. Table 4 and Figure 44 show IMAIN and/or
ISUB/FB vs. brightness data as a percentage of ILED_MAX.
Brightness Main Register
Register Address 0xA0
MSB
1
Bit 7
Data
Bit 6
Data
Bit 5
Data
Bit 4
Data
Bit 3
LSB
Data
Bit 2
Data
Bit 1
Data
Bit 0
Figure 42. Brightness MAIN Register Description
Brightness Sub Register
Register Address 0xB0
MSB
1
Bit 7
Data
Bit 6
Data
Bit 5
Data
Bit 4
Data
Bit 3
LSB
Data
Bit 2
Data
Bit 1
Data
Bit 0
Figure 43. Brightness SUB Register Description
Table 4. ILED vs. Brightness Register Data
BMAIN or
BSUB
Brightness
Data
% of
ILED_MAX
BMAIN or BSUB
Brightness Data
% of ILED_MAX
BMAIN or BSUB
Brightness Data
% of ILED_MAX
BMAIN or
BSUB
Brightness
Data
% of ILED_MAX
0000000
0.000%
0100000
0.803%
1000000
4.078%
1100000
20.713%
0000001
0.166%
0100001
0.845%
1000001
4.290%
1100001
21.792%
0000010
0.175%
0100010
0.889%
1000010
4.514%
1100010
22.928%
0000011
0.184%
0100011
0.935%
1000011
4.749%
1100011
24.122%
0000100
0.194%
0100100
0.984%
1000100
4.996%
1100100
25.379%
0000101
0.204%
0100101
1.035%
1000101
5.257%
1100101
26.701%
0000110
0.214%
0100110
1.089%
1000110
5.531%
1100110
28.092%
0000111
0.226%
0100111
1.146%
1000111
5.819%
1100111
29.556%
0001000
0.237%
0101000
1.205%
1001000
6.122%
1101000
31.096%
0001001
0.250%
0101001
1.268%
1001001
6.441%
1101001
32.716%
0001010
0.263%
0101010
1.334%
1001010
6.776%
1101010
34.420%
0001011
0.276%
0101011
1.404%
1001011
7.129%
1101011
36.213%
0001100
0.291%
0101100
1.477%
1001100
7.501%
1101100
38.100%
0001101
0.306%
0101101
1.554%
1001101
7.892%
1101101
40.085%
0001110
0.322%
0101110
1.635%
1001110
8.303%
1101110
42.173%
0001111
0.339%
0101111
1.720%
1001111
8.735%
1101111
44.371%
0010000
0.356%
0110000
1.809%
1010000
9.191%
1110000
46.682%
0010001
0.375%
0110001
1.904%
1010001
9.669%
1110001
49.114%
0010010
0.394%
0110010
2.003%
1010010
10.173%
1110010
51.673%
0010011
0.415%
0110011
2.107%
1010011
10.703%
1110011
54.365%
0010100
0.436%
0110100
2.217%
1010100
11.261%
1110100
57.198%
0010101
0.459%
0110101
2.332%
1010101
11.847%
1110101
60.178%
0010110
0.483%
0110110
2.454%
1010110
12.465%
1110110
63.313%
0010111
0.508%
0111011
2.582%
1010111
13.114%
1110111
66.611%
0011000
0.535%
0110111
2.716%
1011000
13.797%
1111000
70.082%
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Table 4. ILED vs. Brightness Register Data (continued)
BMAIN or
BSUB
Brightness
Data
% of
ILED_MAX
BMAIN or BSUB
Brightness Data
% of ILED_MAX
BMAIN or BSUB
Brightness Data
% of ILED_MAX
BMAIN or
BSUB
Brightness
Data
% of ILED_MAX
0011001
0.563%
0111000
2.858%
1011001
14.516%
1111001
73.733%
0011010
0.592%
0111001
3.007%
1011010
15.272%
1111010
77.574%
0011011
0.623%
0111010
3.163%
1011011
16.068%
1111011
81.616%
0011100
0.655%
0111011
3.328%
1011100
16.905%
1111100
85.868%
0011101
0.689%
0111100
3.502%
1011101
17.786%
1111101
90.341%
0011110
0.725%
0111101
3.684%
1011110
18.713%
1111110
95.048%
0011111
0.763%
0111111
3.876%
1011111
19.687%
1111111
100.000%
LED Current (% of ILED_MAX)
100%
80%
60%
40%
tSTEP*
20%
0%
00 04 08 0C 10 14 18 1C 20 24 28 2C 30 34 38 3C 40 44 48 4C 50 54 58 5C 60 64 68 6C 70 74 78 7C 7F
BMAIN or BSUB Code (Hex)
* tSTEP is the time between LED current
steps programmed via bits RMP0, RMP1
Figure 44. IMAIN or ISUB vs BMAIN or BSUB Data
Brightness Rate of Change Description
RMP0 and RMP1 control the rate of change of the LED current IMAIN and ISUB/FB in response to changes in
BMAIN and/or BSUB. There are 4 user programmable LED current rates of change settings for the LM3528 (see
Table 5).
Table 5. Rate of Change Bits
RMP0
RMP1
0
0
Change Rate (tSTEP)
12.75µs/step
0
1
3.25ms/step
1
0
6.5ms/step
1
1
13ms/step
For example, if RSET = 12.1kΩ then ILED_MAX = 20mA. With the contents of BMAIN set to 0x7F (IMAIN = 20mA),
suppose the contents of BMAIN are changed to 0x00 resulting in (IMAIN = 0mA). With RMP0 =1 and RMP1 = 1
(13ms/step), IMAIN will change from 20mA to 0mA in 127 steps with 13ms elapsing between steps, excluding the
step from 0x7F to 0x7E, resulting in a full scale current change in 1638ms. The total time to transition from one
brightness code to another is:
ttransition = (|InitialCode
FinalCode|
1) u tSTEP
(3)
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The following 3 additional examples detail possible scenarios when using the brightness register in conjunction
with the rate of change bits and the enable bits.
Example 1:
Step 1: Write to BMAIN a value corresponding to IMAIN = 20mA.
Step 2: Write 1 to ENM (turning on MAIN)
Step 3: IMAIN ramps to 20mA with a rate set by RMP0 and RMP1. (RMP0 and RMP1 bits set the duration spent
at one brightness code before incrementing to the next).
Step 4: ENM is set to 0 before 20mA is reached, thus the LED current fades off at a rate given by RMP0 and
RMP1 without IMAIN going up to 20mA.
Example 2:
Step 1: ENM is 1, and BMAIN has been programmed with code 0x01. This results in a small current into MAIN.
Step 2: BMAIN is programmed with 0x7F (full scale current). This causes IMAIN to ramp toward full-scale at the
rate selected by RMP0 and RMP1.
Step 3: Before IMAIN reaches full-scale BMAIN is programmed with 0x30. IMAIN will continue to ramp to full scale.
Step 4: When IMAIN has reached full-scale value it will ramp down to the current corresponding to 0x30 at a rate
set by RMP0 and RMP1.
Example 3:
Step 1: Write to BMAIN a value corresponding to IMAIN = 20mA.
Step 2: Write a 1 to both RMP0 and RMP1.
Step 3: Write 1 to ENM (turning on MAIN).
Step 4: IMAIN ramps toward 20mA with a rate set by RMP0 and RMP1. (RMP0 and RMP1 bits set the duration
spent at one brightness code before incrementing to the next).
Step 5: After 1.222s IMAIN has ramped to 19.687% of ILED_MAX (0.19687 × 20mA = 3.9374mA). Simultaneously,
RMP0 and RMP1 are both programmed with 0.
Step 6: IMAIN continues ramping from 3.9374mA to 20mA, but at a new ramp rate of 12.75µs/step.
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Table 6. HPG Register Function
Bits 7 – 6
(PGEN Bit
Period)
Bits 5 - 3 (PGEN
Enable/Disable and
Duty Cycle
Selection)
Bit 2
(GPIO
Data)
Bit 1 (GPIO
Data
Direction)
Bit 0
(HWEN
Control)
X
X
X
X
0
HWEN/PGEN/GPIO is configured as an active high
Hardware Enable Input (HWEN)
00 = 1.6µs/bit
(625kHz)
01 = 26ms/bit
(38Hz)
10 = 52ms/bit
(19Hz)
11 = 105ms/bit
(9.5Hz)
001 = 100%
010 = 1/2
011 = 1/3
100 = 1/4
101 = 1/6
110 = 1/12
111 = Latch Pattern
Into Shift Register
X
X
1
HWEN/PGEN/GPIO is configured as a Pattern Generator
Output with the frequency set by bits <7:6> and the duty
cycle set by bits <5:3>. (See Figure 46.)
X
000
GPIO
Read Data
1
1
HWEN/PGEN/GPIO is configured as a GPIO Input. Read
data from bit 2.
X
000
GPIO
Write Data
0
1
HWEN/PGEN/GPIO is configured as a GPIO Output. A ‘1’
written to bit 2 will force HWEN/PGEN/GPIO high; a 0
written to bit 2 will force HWEN/PGEN/GPIO low.
(1)
Function
(2)
(1)
(2)
This represents the amount of time each programmed bit will be present at HWEN/PGEN/GPIO. The entire pattern period will be 32 ×
Bit Period.
This duty cycle indicates the fraction of time the pattern is being output at HWEN/PGEN/GPIO. For example the 1/2 duty cycle (bits
<5:3> = 010) will have the 32 bit pattern output once followed by a dead time (HWEN/PGEN/GPIO high impedance) equal to 1×’s the
pattern period (Deadtime = 32 × Bit_Period × (1/DutyCycle -1). For the 100% duty cycle setting the 32 bit pattern will repeat constantly
with no deadtime.
HWEN/PGENGPIO Register
Register Address 0x80
Power On Reset = 0x01
MSB
Frequency
Selection
Bit 7
Frequency
Selection
Bit 6
Duty Cycle
Selection
Bit 5
Duty Cycle
Selection
Bit 4
Duty Cycle
Selection
Bit 3
LSB
GPIO
Data
Bit 2
GPIO
Data
Direction
Bit 1
HWEN
Enable/
Disable
Bit 0
Figure 45. HPG Register Description
Table 7. GPIO Register Function
Bits 7 - 2
GPIO Data (Bit 1)
Data Direction (Bit 0)
Function
X
X
0
GPIO is configured as a GPIO
input with the input data read
back via bit [1]. This is the default
power on state.
X
X
1
GPIO is configured as a logic
output. The output logic voltage
is written to bit [1].
GPIO Register
Register Address 0x81
Power On Reset = 0xFC
MSB
1
Bit 7
1
Bit 6
1
Bit 5
1
Bit 4
1
Bit 3
LSB
1
Bit 2
Data
Bit 1
Data
Direction
Bit 0
Figure 46. GPIO Register Description
Figure 47 – Figure 50 detail the Pattern Generator Data Registers. These hold the 32 bit data that is output at
HWEN/PGEN/GPIO in PGEN mode. The data is output LSB first (Bit 0 of PGEN0) and MSB last (Bit 7 of
PGEN3).
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PGEN0 Register
Register Address 0x90
Power On Reset = 0x00
MSB
PGEN
DATA 7
Bit 7
PGEN
DATA 6
Bit 6
PGEN
DATA 5
Bit 5
PGEN
DATA 4
Bit 4
PGEN
DATA 3
Bit 3
LSB
PGEN
DATA 2
Bit 2
PGEN
DATA 1
Bit 1
PGEN
DATA 0
Bit 0
Figure 47. PGEN0 Register Description
PGEN1 Register
Register Address 0x91
Power On Reset = 0x00
MSB
PGEN
DATA 15
Bit 7
PGEN
DATA 14
Bit 6
PGEN
DATA 13
Bit 5
PGEN
DATA 12
Bit 4
PGEN
DATA 11
Bit 3
LSB
PGEN
DATA 10
Bit 2
PGEN
DATA 9
Bit 1
PGEN
DATA 8
Bit 0
Figure 48. PGEN1 Register Description
PGEN2 Register
Register Address 0x92
Power On Reset = 0x00
MSB
PGEN
DATA 23
Bit 7
PGEN
DATA 22
Bit 6
PGEN
DATA 21
Bit 5
PGEN
DATA 20
Bit 4
PGEN
DATA 19
Bit 3
LSB
PGEN
DATA 18
Bit 2
PGEN
DATA 17
Bit 1
PGEN
DATA 16
Bit 0
Figure 49. PGEN2 Register Description
PGEN3 Register
Register Address 0x93
Power On Reset = 0x00
MSB
PGEN
DATA 31
Bit 7
PGEN
DATA 30
Bit 6
PGEN
DATA 29
Bit 5
PGEN
DATA 28
Bit 4
PGEN
DATA 27
Bit 3
LSB
PGEN
DATA 26
Bit 2
PGEN
DATA 25
Bit 1
PGEN
DATA 24
Bit 0
Figure 50. PGEN3 Register Description
Figure 51 shows a write sequence to the pattern generator programmed to output the waveform in Figure 52. In
this example HPG register bits <7:6> = 01 (for 26ms/bit) and bits <5:3> = 010 (for 1/2 duty cycle). The pattern
data in registers (PGEN0 – PGEN2) are all loaded with 0xAC. A ‘1’ will force the HWEN/PGEN/GPIO output low
while a ‘0’ will force HWEN/PGEN/GPIO open drain. When set for a 26ms/bit period the pattern will be output
LSB first (PGEN0, bit 0) and repeat every
tPERIOD =
26 ms/bit u 32 bits
= 1.664s
1/2 Dutycycle
(4)
When set for ½ duty cycle there will be a dead time (HWEN/PGEN/GPIO high impedance) between each pattern
and equal to the pattern period. In applications where HWEN/PGEN/GPIO is used to pull current through an
indicator LED a ‘1’ corresponds to the LED on and a ‘0’ corresponds to the LED off.
22
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S
0x36
R/W= 0
ACK
0x90
ACK
0XAC
ACK
S
0x36
R/W= 0
ACK
0x91
ACK
0XAC
ACK
S
0x36
R/W= 0
ACK
0x92
ACK
0XAC
ACK
S
0x36
R/W= 0
ACK
0x93
ACK
0XAC
ACK
S
0x36
R/W= 0
ACK
0x80
ACK
bXX111XXX*
ACK
S
0x36
R/W= 0
ACK
0x80
ACK
0x51
ACK
*Only bits <5:3> Œ v •• ŒÇ ]v šZ]• Çš šZ Œ •š Œ }v[š Œ •. Bits <5:3> = Z111[ Œ
necessary to latch the pattern generator data bits into the internal shift register.
Figure 51. Pattern Generation Write Sequence
HPG Bits <7:6> = 01 (26 ms/bit)
HPG Bits <5:3> = 010 (1/2 Duty Cycle)
Bit 7
Bit 0
26 ms/bit
PGEN0 Data
= 0xAC
PGEN1 Data
= 0XAC
PGEN2 Data
= 0XAC
PGEN3 Data
= 0XAC
Figure 52. Pattern Generation Output
Shutdown and Output Isolation
The LM3528 provides a true shutdown for either MAIN or SUB/FB when configured as a White LED bias supply.
Write a 0 to ENM (bit 1) of the General Purpose register to turn off the MAIN current sink and force MAIN high
impedance. Write a 0 to ENS (bit 2) of the General Purpose register to turn off the SUB/FB current sink and force
SUB/FB high impedance. Writing a 1 to ENM or ENS turns on the MAIN and SUB/FB current sinks respectively.
When in shutdown the leakage current into MAIN or SUB/FB is typically 1.8µA. See Typical Performance
Characteristics Plots for start-up responses of the LM3528 using the ENM and ENS bits in White LED and OLED
modes.
Application Information
LED Current Setting/Maximum LED Current
Connect a resistor (RSET) from SET to GND to program the maximum LED current (ILED_MAX) into MAIN or
SUB/FB. The RSET to ILED_MAX relationship is:
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ILED_MAX = 192 u
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1.244V
RSET
(5)
where SET provides the constant 1.244V output.
Output Voltage Setting (OLED Mode)
Connect Feedback resistors from the converters output to SUB/FB to GND to set the output voltage in OLED
mode (see R1 and R2 in the Figure 1 (OLED Panel Power Supply). First select R2 < 100kΩ then calculate R1
such that:
·
§V
R1 = R 2 ¨ OUT - 1¸
1.21V
¹
©
(6)
In OLED mode the MAIN current sink continues to regulate the current through MAIN, however, VMAIN is no
longer regulated. To avoid dropout and ensure proper current regulation the application must ensure that VMAIN >
0.3V.
Input Capacitor Selection
Choosing the correct size and type of input capacitor helps minimize the input voltage ripple caused by the
switching of the LM3528’s boost converter. For continuous inductor current operation the input voltage ripple is
composed of 2 primary components, the capacitor discharge (delta VQ) and the capacitor’s equivalent series
resistance (delta VESR). These ripple components are found by:
'VQ =
'I L x D
2 x f SW x C IN
and
'VESR = 2 x 'I L x R ESR
where 'I L =
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
(7)
In the typical application circuit a 1µF ceramic input capacitor works well. Since the ESR in ceramic capacitors is
typically less than 5mΩ and the capacitance value is usually small, the input voltage ripple is primarily due to the
capacitive discharge. With larger value capacitors such as tantalum or aluminum electrolytic the ESR can be
greater than 0.5Ω. In this case the input ripple will primarily be due to the ESR.
Output Capacitor Selection
The LM3528’s output capacitor supplies the LED current during the boost converters on time. When the switch
turns off the inductor energy is discharged through the diode supplying power to the LED’s and restoring charge
to the output capacitor. This causes a sag in the output voltage during the on time and a rise in the output
voltage during the off time. The output capacitor is therefore chosen to limit the output ripple to an acceptable
level depending on LED or OLED panel current requirements and input/output voltage differentials. For proper
operation ceramic output capacitors ranging from 1µF to 2.2µF are required.
As with the input capacitor, the output voltage ripple is composed of two parts, the ripple due to capacitor
discharge (delta VQ) and the ripple due to the capacitors ESR (delta VESR). For continuous conduction mode, the
ripple components are found by:
'VQ =
ILED u (VOUT
fSW u VOUT u COUT
'VESR = RESR u
where
24
VIN)
'IL =
and
§ ILED u VOUT
·
+ 'IL¸
¨ VIN
©
¹
VIN u (VOUT
VIN)
2 u fSW u L u VOUT
(8)
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Table 8 lists different manufacturers for various capacitors and their case sizes that are suitable for use with the
LM3528. When configured as a dual output LED driver a 1µF output capacitor is adequate. In OLED mode for
output voltages above 12V a 2.2µF output capacitor is required (see Low Output Voltage Operation (OLED)
Section).
Table 8. Recommended Output Capacitors
Manufacturer
Part Number
Value
Case Size
Voltage Rating
TDK
C1608X5R1E105M
1µF
0603
25V
Murata
GRM39X5R105K25D539
1µF
0603
25V
TDK
C2012X5R1E225M
2.2µF
0805
25V
Murata
GRM219R61E225KA12
2.2µF
0805
25V
Inductor Selection
The LM3528 is designed for use with a 10µH inductor, however 22µH are suitable providing the output capacitor
is increased 2×. When selecting the inductor ensure that the saturation current rating (ISAT) for the chosen
inductor is high enough and the inductor is large enough such that at the maximum LED current the peak
inductor current is less than the LM3528’s peak switch current limit. This is done by choosing:
ISAT >
'IL =
I LED VOUT
+ 'I L
×
K
VIN
VIN x (VOUT - VIN )
2 x f SW x L x VOUT
where
, and
VIN x (VOUT - VIN)
L>
§
2 x f SW x VOUT x ¨
¨I PEAK -
I LED _ MAX x VOUT ·
©
¸¸
¹
K x VIN
(9)
Values for IPEAK can be found in the plot of peak current limit vs. VIN in the Typical Performance Characteristics
graphs. Table 9 shows possible inductors, as well as their corresponding case size and their saturation current
ratings.
Table 9. Recommended Inductors
Manufacture
r
Part Number
Value
Dimensions
ISAT
DC Resistance
TDK
VLF3012AT-100MR49
10µH
2.6mm×2.8mm×1mm
490mA
0.36Ω
Coilcraft
LPS3008-103ML
10µH
2.95mm×2.95mm×0.8mm
490mA
0.65Ω
TDK
VLF4012AT-100MR79
10µH
3.5mm×3.7mm×1.2mm
800mA
0.3Ω
Coilcraft
LPS4012-103ML
10µH
3.9mm×3.9mm×1.1mm
700mA
0.35Ω
TOKO
A997AS-100M
10µH
3.8mm×3.8mm×1.8mm
580mA
0.18Ω
Diode Selection
The output diode must have a reverse breakdown voltage greater than the maximum output voltage. The diodes
average current rating should be high enough to handle the LM3528’s output current. Additionally, the diodes
peak current rating must be high enough to handle the peak inductor current. Schottky diodes are recommended
due to their lower forward voltage drop (0.3V to 0.5V) compared to (0.6V to 0.8V) for PN junction diodes. If a PN
junction diode is used, ensure it is the ultra-fast type (trr < 50ns) to prevent excessive loss in the rectifier. For
Schottky diodes the B05030WS (or equivalent) work well for most designs. See Table 10 for a list of other
Schottky Diodes with similar performance.
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Table 10. Recommended Schottky Diodes
Manufacturer
Part Number
Package
Reverse
Breakdown Voltage
Average
Current
Rating
On Semiconductor
NSR0230P2T5G
SOD-923 (0.8mm×0.6mm×0.4mm)
30V
200mA
On Semicondcuctor
NSR0230M2T5G
SOD-723 (1mm×0.6mm×0.52mm)
30V
200mA
On Semiconductor
RB521S30T1
SOD-523 (1.2mm×0.8mm×0.6mm)
30V
200mA
Diodes Inc.
SDM20U30
SOD-523 (1.2mm×0.8mm×0.6mm)
30V
200mA
Diodes Inc.
B05030WS
SOD-323 (1.6mm×1.2mm×1mm)
30V
0.5A
Philips
BAT760
SOD-323 (1.6mm×1.2mm×1mm)
20V
1A
Output Current Range (OLED Mode)
The maximum output current the LM3528 can deliver in OLED mode is limited by 4 factors (assuming continuous
conduction); the peak current limit of 770mA (typical), the inductor value, the input voltage, and the output
voltage. Calculate the maximum output current (IOUT_MAX) using the following equation:
(IPEAK
IOUT_MAX =
where
'IL =
'IL) u K u VIN
VOUT
VIN u (VOUT
VIN)
2 u fSW u L u VOUT
(10)
For the typical application circuit with VOUT = 18V and assuming 70% efficiency, the maximum output current at
VIN = 2.7V will be approximately 70mA. At 4.2V due to the shorter on times and lower average input currents the
maximum output current (at 70% efficiency) jumps to approximately 105mA. Figure 53 shows a plot of IOUT_MAX
vs. VIN using the above equation, assuming 80% efficiency. In reality, factors such as current limit and efficiency
will vary over VIN, temperature, and component selection. This can cause the actual IOUT_MAX to be higher or
lower.
Figure 53. Typical Maximum Output Current in OLED Mode (assumed 80% efficiency)
Output Voltage Range (OLED Mode)
The LM3528's output voltage is constrained by 2 factors. On the low end it is limited by the minimum duty cycle
of 10% (assuming continuous conduction) and on the high end it is limited by the over voltage protection
threshold (VOVP) of 22V (typical). In order to maintain stability when operating at different output voltages the
output capacitor and inductor must be changed. Refer to Table 10 for different VOUT, COUT, and L combinations.
26
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Table 11. Component Values for Output Voltage Selection
VOUT
COUT
L
VIN Range
18V
2.2µF
10µH
2.7V to 5.5V
15V
2.2µF
10µH
2.7V to 5.5V
12V
4.7µF
10µH
2.7V to 5.5V
9V
10µF
10µH
2.7V to 5.5V
7V
10µF
4.7µH
2.7V to 5.5V
5V
22µF
4.7µH
2.7V to 4.5V
Application Circuits
10 PH
VOLED = 18V
20 mA
2.7V to 5.5V
IN
SW
OVP
CIN
1 PF
VIO
10 k:
40 mA
COUT
2.2 PF
OLED
Display
LM3528
10 k:
R2
10 k:
MAIN
SCL
SDA
R1
140 k:
SUB/FB
HWEN/
PGEN/GPIO
GPIO
Current
Limiting
Resistor
SET
PGND
RSET
12.1 k:
1 M:
Indicator
LED
OLED Panel Power Supply With Indicator LED
Figure 54. LED Backlight + OLED Power Supply
Layout Considerations
Refer to AN-1112 SNVA009 for DSBGA package soldering
The high switching frequencies and large peak currents in the LM3528 make the PCB layout a critical part of the
design. The proceeding steps should be followed to ensure stable operation and proper current source
regulation.
1. CIN should be located on the top layer and as close to the device as possible. The input capacitor supplies the
driver currents during MOSFET switching and can have relatively large spikes. Connecting the capacitor close to
the device will reduce the inductance between CIN and the LM3528 and eliminate much of the noise that can
disturb the internal analog circuitry.
2. Connect the anode of the Schottky diode as close to the SW pin as possible. This reduces the inductance
between the internal MOSFET and the diode and minimizes the noise generated from the discontinuous diode
current and the PCB trace inductance that will add ringing at the SW node and filter through to VOUT. This is
especially important in VOUT mode when designing for a stable output voltage.
3. COUT should be located on the top layer to minimize the trace lengths between the diode and PGND. Connect
the positive terminal of the output capacitor (COUT+) as close as possible to the cathode of the diode. Connect
the negative terminal of the output capacitor (COUT-) as close as possible to the PGND pin on the LM3528. This
minimizes the inductance in series with the output capacitor and reduces the noise present at VOUT and at the
PGND connection. This is important due to the large di/dt into and out of COUT. The returns for both CIN and
COUT should terminate directly to the PGND pin.
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4. Connect the inductor on the top layer close to the SW pin. There should be a low impedance connection from
the inductor to SW due to the large DC inductor current, and at the same time the area occupied by the SW node
should be small so as to reduce the capacitive coupling of the high dV/dt present at SW that can couple into
nearby traces.
5. , Route the traces for RSET and the feedback divider away from the SW node to minimize the capacitance
between these nodes that can couple the high dV/dt present at SW into them. Furthermore, the feedback divider
and RSETshould have dedicated returns that terminate directly to the PGND pin of the device. This will minimize
any shared current with COUT or CIN that can lead to instability. Avoide routing the SUB/FB node close to other
traces that can see high dV/dt such as the I2C pins. The capacitive coupling on the PCB between FB and these
nodes can disturb the output voltage and cause large voltage spikes at VOUT.
6. Do not connect any external capacitance to the SET pin.
7. Refer to the LM3528 Evaluation Board as a guide for proper layout.
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REVISION HISTORY
Changes from Revision A (May 2013) to Revision B
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 28
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PACKAGE OPTION ADDENDUM
www.ti.com
2-May-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Op Temp (°C)
Top-Side Markings
(3)
(4)
LM3528TME/NOPB
ACTIVE
DSBGA
YFQ
12
250
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
-40 to 85
SE
LM3528TMX/NOPB
ACTIVE
DSBGA
YFQ
12
3000
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
-40 to 85
SE
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a
continuation of the previous line and the two combined represent the entire Top-Side Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE MATERIALS INFORMATION
www.ti.com
8-May-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
LM3528TME/NOPB
DSBGA
YFQ
12
250
178.0
8.4
LM3528TMX/NOPB
DSBGA
YFQ
12
3000
178.0
8.4
Pack Materials-Page 1
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
1.35
1.75
0.76
4.0
8.0
Q1
1.35
1.75
0.76
4.0
8.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
8-May-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM3528TME/NOPB
DSBGA
YFQ
LM3528TMX/NOPB
DSBGA
YFQ
12
250
210.0
185.0
35.0
12
3000
210.0
185.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
YFQ0012xxx
D
0.600
±0.075
E
TMD12XXX (Rev B)
D: Max = 1.64 mm, Min = 1.58 mm
E: Max = 1.24 mm, Min = 1.18 mm
4215079/A
NOTES:
A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
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12/12
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Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
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Copyright © 2013, Texas Instruments Incorporated
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