LM3509_08 Datasheet, PDF (1/24 Pages) National Semiconductor (TI) – High Efficiency Boost for White LED

March 6, 2008
LM3509
High Efficiency Boost for White LED's and/or OLED
Displays with Dual Current Sinks and I²C Compatible
Brightness Control
General Description
The LM3509 current mode boost converter offers two sepa-
rate 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.
When configured as a dual output white LED bias supply, the
LM3509 adaptively regulates the supply voltage of the LED
strings to maximize efficiency and insure the current sinks re-
main in regulation. The maximum current per output is set via
a single external low power resistor. An I²C compatible inter-
face allows for independent adjustment of the LED current in
either output from 0 to max current in 32 exponential steps.
When configured as a white LED + OLED bias supply the
LM3509 can independently and simultaneously drive a string
of up to 5 white LED’s and deliver a constant output voltage
of up to 21V for OLED panels.
Output over-voltage protection shuts down the device if
V_OUT rises above 21V allowing for the use of small sized low
voltage output capacitors. The LM3509 is offered in a small
10-pin thermally- enhanced LLP package and operates over
the -40°C to +85°C temperature range.
Features
■ ^{Integrated OLED Display Power Supply and LED Driver}
■ ^{Drives up to 10 LED’s at 30mA}
■ ^{Drives up to 5 LED’s at 20mA and delivers up to 21V at}
40mA
■ ^{Over 90% Efficient}
■ ^{32 Exponential Dimming Steps}
■ ^{0.15% Accurate Current Matching Between Strings}
■ ^{Internal Soft-Start Limits Inrush Current}
■ ^{True Shutdown Isolation for LED’s}
■ ^{Wide 2.7V to 5.5V Input Voltage Range}
■ ^{21V Over-Voltage Protection}
■ ^{1.27MHz Fixed Frequency Operation}
■ ^{Low Profile 10-pin LLP Package (3mm x 3mm x 0.8mm)}
■ ^{General Purpose I/O}
■ ^{Active Low Hardware Reset}
Applications
■ ^{Dual Display LCD Backlighting for Portable Applications}
■ ^{Large Format LCD Backlighting}
■ ^{OLED Panel Power Supply}
Typical Application Circuits
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