OB3350 FEATURES GENERAL DESCRIPTION

OB3350 FEATURES GENERAL DESCRIPTION
OB3350
Cost Effective LED Controller
FEATURES
GENERAL DESCRIPTION
OB3350 is a highly integrated and cost effective
Light Emitting Diode (LED) driver optimized for
LCD monitor and LCD TV backlighting application.
It provides a high performance LED backlight
solution with minimized BOM count.
The OB3350 contains a PWM boost driver which
uses current mode control and fixed frequency
operation to regulate the LED current. The LED
current is sensed through an external current
sense resistor. The voltage across the sensing
resistor is compared with reference level of 300mV,
the error is amplified to control the pulse width of
the power switch thus to regulate the current
flowing the LED.
The OB3350 offers external low frequency PWM
(LPWM) dimming method for a wide range of
dimming control.
The OB3350 offers comprehensive protection
such as power MOSFET over current protection
(OCP), output over voltage protection (OVP), IC
power supply under voltage lockout (UVLO), and
LED open protection.
Current Mode PWM Controller With Good
Dynamic Response
8V to 35V Input Voltage Range
External PWM Dimming Mode
Over Voltage Protection
Over Current Protection
Under Voltage Lockout (UVLO)
Thermal Shutdown
APPLICATIONS
LCD Monitor
LCD TV
Flat panel display
The OB3350
SOP-8 Packages.
3350 is offered in SOP
TYPICAL APPLICATION
Figure1. OB3350 Typical Application Schematic
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Preliminary datasheet
OB_DOC_DS_335000
-1-
Free Datasheet http://www.datasheetlist.com/
OB3350
Cost Effective LED Controller
Recommended Operating Range
Absolute Maximum Ratings
Parameter
Value
VIN Input Voltage to GND
-0.3V to 40V
I/O to GND
-0.3V to 7V
Operating Ambient Temp. TA
-40 ~ 85
Operating Junction Temp. TJ
-40 ~ 150
Min/Max Storage Temp. Tstg
-55 ~150
Lead Temp. (10 Sec)
260
Note: Stresses beyond those listed under “absolute maximum
Parameter
Vin Voltage
Burst Dimming Frequency
Value
8V to 35V
100Hz to 1KHz
Package Thermal Characteristics
Parameter
Thermal Resistance JA
(SOP)
Value
150
/W
ratings” may cause permanent damage to the device. These
Ordering Information
are stress ratings only, functional operation of the device at
these or any other conditions beyond those indicated under
Part Number
OB3350CP
OB3350CPA
CPA
“recommended operating conditions” is not implied. Exposure
to absolute maximum-rated conditions for extended periods
Description
SOP8,
8, pb-free in tube
SOP8,
SOP8 pb-free
free in T
T&R
may affect device reliability.
OB3350
X
X
Package
X
Package Pb- free
Cost Effective LED Controller
C:SOP8
P:Pb-free
Packing
Blank:Tube
A: Taping
Package Marking Information
Y:Year Code
WW:Week Code(01-52)
ZZZ:Lot Code
C:SOP8 Package
P:Pb-free Package
S:Internal Code(Optional)
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Preliminary datasheet
OB_DOC_DS_335000
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Free Datasheet http://www.datasheetlist.com/
OB3350
Cost Effective LED Controller
Pin Configuration
VIN
1
8
PWM
GATE
2
7
OVP
GND
3
6
COMP
CS
4
5
FB
OB3350
No.
Name
I/O
Pin Function
1
VIN
Power
Power Supply Input
2
GATE
I/O
Gate Driver Output Pin
3
GND
GND
Ground
4
CS
I/O
Current Sense Input
5
FB
I/O
LED Current Feedback Input
6
COMP
I/O
Boost Converter Loop Compensation Pin
7
OVP
I/O
Over Voltage Protection Sense Input
8
PWM
I/O
O
External PWM Dimming Control
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Preliminary datasheet
OB_DOC_DS_335000
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Free Datasheet http://www.datasheetlist.com/
OB3350
Cost Effective LED Controller
Functional Block Diagram
UVLO
DIM
OSC
VIN
Ramp
Adjust
5V
Thermal
Shutdown
Reference
Soft-start
PW
M
S
COMP
Control
Logic
Gate
Drive
GATE
PWM
Comparator
EA
FB
Vth_ovp
DIM
Control
PWM
Sense
Amplifer
GND
CS
OVP
O
VP
P
Figure2. OB3350 Functional Block Diagram
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Preliminary datasheet
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OB3350
Cost Effective LED Controller
Electrical Characteristics
VDDH=12V,PWM=5V, TA=25
Parameter
Current Consumption
Input voltage range
, if not otherwise noted.
Symbol
Conditions
Vin=12V,PWM=5V no
load
PWM low >50ms sleep
mode
Operating supply current
IVDD
Stand by current
IVDD _ STB
VDD UVLO
UVLO
UVLO Hysteresis
Soft start
UVLO(ON)
UVLO(Hys)
Soft start slope
I sst _ slop
PWM Control
Operating frequency
Max duty cycle
PWM Input Threshold
Min
Typ
Max Units
8
-
35
V
-
2.5
3
mA
-
310
400
uA
6
7
500
8
V
mV
400
FOSC
Dmax
PWM(high)
PWM(low)
175
93
High Level
Low Level
Vref _ ea
Reference voltage at
inverting input
non-inverting
mV/mS
200
95
225
97
2.5
2
KHz
%
V
V
0.289
0.3
0.311
V
80
70
100
120
dB
uA/V
1
1.3
Error Amplifier
Reference voltage
Open loop voltage gain
Transconductance of EA
Am
Gm
Output source current
I source
24
30
36
uA
Output sink current
I sin k
48
60
72
uA
1.8
2.0
2.2
V
Protection Threshold
Threshold of output
over voltage
Threshold
of
over
current
protection
(duty=90%)
OVP
VOVP OV
OCP
Vth_OCP
_OCP
OTP ON
TOTP _ ON
140
160
180
OTP OFF
TOTP _ OFF
120
140
160
Connect detect time
Tdio
OVP UVLO threshold
VOVP UV
330
Normal operation
System startup
mV
1
mS
200
100
mV
mV
Gate Driver Output
Gate rise time
Trise
500pF load
Gate fall time
T fall
500pF load
©On-Bright Electronics
Confidential
-
40
80
ns
20
40
ns
Preliminary datasheet
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OB3350
Cost Effective LED Controller
Function Description
switching operation when the voltage at pin VIN
increases to a voltage above 7.5V.
General Operation
LED Current Regulation
The OB3350 is a LED driver designed for boost
DC-DC converters in a constant frequency mode.
The controller implements a peak current mode
control scheme and an internal transconductance
amplifier to accurately control the output current
over a wide input and load conditions.
Low frequency PWM dimming input that can
accept an external control signal with a duty ratio
of 1%-100%. OB3350 offers comprehensive
protection features to protect the system in various
fault conditions such as output over voltage
protection, boost diode disconnection protection
and output short circuit protection. The
cycle-by-cycle current limit function limits the
maximum current flowing through the external
MOSFET. The over temperature protection
ensures that the system will not run into condition
of thermal runaway and blow up.
The LED current is sensed by current sense
resistors connected between pin FB and GND.
The sensed error signal is amplified and compared
to the CS pin sensing current signal plus the slope
compensation to determine the on-time
time of the
switching MOSFET. The error amplifier sources or
sinks the current to the COMP pin to adjust the
required inductor current as the load changes.
changes The
slope-compensation
compensation signal is added to the
current-sense
sense signal to improve the stability at high
duty cycles.
The average LED current is approximated by the
following equation
300[ mV ]
I LED [mA]
R FB [ ]
At light loading, the OB
OB3350 automatically skips
some pulses to improve efficiency and prevent
overcharging the output capacitor
capacitor. In this
pulse-skipping mode
mode, the inductor current ramps
up for a minimum on
on-time (typical 300ns), then
deliver the stored energy to the output. The switch
remains off until another pulse is needed to boost
the output voltage
voltage.
Startup
OB3350 is enabled by applying a voltage of
greater than approximately 2.5V to PWM pin. An
on-chip internal 150kk ohm pull down resistor is
inserted between PWM pin and ground. When the
first rising edge is applied to PWM input,, also the
pin of PWM is logic high, the OB3350 will power up
immediately, and remains power up until the PWM
input has been hold low for at least 50ms(typ)
50ms(typ), at
this time the chip will enter sleep mode. At sleep
mode, the power of theOB3350
3350 will be lower than
400uA (typ).
Once OB3350 is enabled the internal 5V regulator
will be activated to source a current less than 4mA
to the whole chip.
When PWM is active high, the OB3350
checks the
OB
topology connection first. The chip monitors the
OVP pin to see if the Schottky diode (boost diode)
is connected or the boost output is short to GND
GND, if
the voltage at OVP pin is lower than 100mV, the
output will be disabled.
disabled The OB3350 will also
check other faults (UVLO, OCP and OTP), if there
is no fault, then the boost converter will boost up
the output with the internal soft start
start.
Slope Compensation
The OB3350 uses a current mode control scheme.
The main advantages of current mode control are
inherent cycle-by-cycle current limit for the switch
and simpler control loop characteristics. However,
current mode control has an inherent instability for
duty cycles greater than 50%, which is also called
sub-harmonic oscillation. The OB3350 has a
build-in slope compensation to avoid sub-harmonic
oscillation.
UVLO
An under-voltage lockout protection feature with a
hysteresis of about 300mv is provided for VDDH.
When the voltage at this pin exceeds a threshold
of approximately 7.5V (typ), the IC starts the
normal operation. If the voltage at this pin drops
below a threshold of approximately 7(typ) V, the IC
stops switching operation. The IC resumes
©On-Bright Electronics
Figure4 Sub-harmonic oscillation at duty>50%
and compensation slope to avoid sub-harmonic
oscillation
If the control signal (which applied to the negative
input of the PWM comparator) has no slope and
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OB3350
Cost Effective LED Controller
the slope which representing inductor current ramp
up until the comp signal is reached, then ramp
down. If the duty > 50%, any distribution won’t be
converged from duty to duty and thus
sub-harmonic oscillation happens. For the
equation below:
S f Se
I ( n 1)
I ( n)
Sn Se
To avoid sub-harmonic oscillation happening, just
make sure (Sf-Se) / (Sn+Se) smaller than 1.
For boost applications, the slopes Se, Sf and Sn
can be calculated with the formulas below and a
typical value of VSL is 50mV.
S e VSL f s
Sf
R sen
Vout
Dimming Control
The LED brightness is controlled by the PWM
signal at PWM pin which has different duty cycle.
OB3350 can accept an external PWM signal to
PWM pin in the range of 100Hz to 1 KHz with a
swing voltage of 0V to a level greater than 2.5V.
OVP Protection
OB3350 shuts down the output if the output
voltage is higher than the predetermined threshold
level. In case of LED failing, the current of LED
and the resulted voltage drop on sensing resistor
is nearly zero; the converter will run at maximum
duty cycle that boosts the output voltage to a very
high level. To prevent this happen,
happen, the output
voltage is monitored through Pin OVP and
converter is shut down
n if the output voltage
exceeds the predetermined level.
level This protection
is latched and OB3350 can be reset from VIN or
PWM.
Vin / L
S n R sen Vin / L
When Se increases then the factor which can
determine whether the sub-harmonic oscillation
will occur decreases. When the duty cycle is
greater than 50% and the inductance becomes
less, the factor increases. And for more flexibility
slope compensation amplitude can be increased
by adding one external resistor, RSL, in the CS
path. Figure 4 shows the setup. The externally
generated slope compensation is then added to
3350.
the internal slope compensation of the OB3350.
When using external slope compensation,, the
formula for Se becomes:
S e (VSL I s RSL ) f s
A typical value of Is is 40uA.
VOUT SHORT Protection
VOUT short condition is monitored by the voltage
at pins OVP. During normal operation, when the
voltage at OVP pin drops below a threshold of
approximately 0.2V, the VOUT-short protection
function is activated and the GATE is turned off.
off
This state is latched and can be reset from VIN or
PWM.
PWM
Thermal Shutdown
The OB3350 includes a thermal protection circuit.
When the junction temperature exceeds 160°C
(typical), the controller and current sources shut
down and do not restart until the junction
temperature drops below 140°C (typical).
Figure5 Adding external slope compensation to OB
OB3350
It’s good design practice to only add as much
slope compensation as needed to avoid
sub-harmonic
oscillation.
Additional
slope
compensation minimized the influence of the
sensed current in the control loop. With very large
slope
compensation
the
control
loop
characteristics are similar to a voltage mode
regulator which compares the error voltage to a
saw tooth waveform rather than the inductor
current.
©On-Bright Electronics
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Preliminary datasheet
OB_DOC_DS_335000
-7-
Free Datasheet http://www.datasheetlist.com/
OB3350
Cost Effective LED Controller
Reference Application
Figure6. OB3350 for external LPWM dimming Reference Application Schematic
©On-Bright Electronics
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Preliminary datasheet
OB_DOC_DS_335000
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OB3350
Cost Effective LED Controller
PACKAGE MECHANICAL DATA
Symbol
A
A1
1
A2
2
b
c
D
E
E1
E
e
L
©On-Bright Electronics
Dimensions In Millimeters
Min
Max
1.350
1.750
1
0.050
0
050
0
0.250
1
1.250
1.650
0.310
0.510
0.100
0.250
4.700
5.150
3.800
4.000
5.800
5
6.200
1.270 (BSC)
0.400
1.270
0º
8º
Confidential
Dimensions In Inches
Min
Max
0.053
0.069
0.002
0.010
0.049
0.065
0.012
0.020
0.004
0.010
0.185
0.203
0.150
0.157
0.228
0.244
0.050 (BSC)
0.016
0.050
0º
8º
Preliminary datasheet
OB_DOC_DS_335000
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FreeDatasheethttp://www.datasheetlist.com/
OB3350
Cost Effective LED Controller
Important Notice
Right to make changes
On-Bright Electronics Corp. reserves the right to make corrections, modifications, enhancements,
improvements, and other changes to its products and services at any time and to discontinue any product
or service without notice. Customers should obtain the latest relevant information before placing orders
and should verify that such information is current and complete.
Warranty information
On-Bright Electronics Corp. warrants performance of its hardware products to the
he specifications applicable
at the time of sale in accordance with its standard warranty. Testing and other quality control techniques
are used to the extent it deems necessary to support this warranty. Except where mandated by
government requirements, testing of all parameters of each product is not necessarily performed.
performed
On-Bright Electronics Corp. assumes no liability for applications assistance
design.
ance or customer product design
Customers are responsible for their products and applications using On-Bright’s components, data sheet
and application notes. To minimize the risks associated
ciated with customer products and applications,
applications
customers should provide adequate design and operating safeguards.
Life support
On-Bright Electronics Corp.’s products are not designed
ed to be used as components in devices intended to
support or sustain human life. On-bright Electronics Corp. will not be held liable for any damages or claims
resulting from the use of its products in medical applications.
Military
On-Bright Electronics Corp.’s products are not designed for use in military applications. On-Bright
Electronics Corp. will not be held liable for any damages or claims resulting from tthe use of its products in
military applications.
©On-Bright Electronics
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Preliminary datasheet
OB_DOC_DS_335000
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Free Datasheet http://www.datasheetlist.com/
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