The LM3509 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 outut (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 ensure the current sinks remain in regulation. The maximum current per output is set via a single external low power resistor. An I 2 C compatible interface 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 VOUT 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°temperature range.
The LM3509SD evaluation board is set-up to drive 2 strings of 5 white LEDs (OSRAM, LW_M67C, VF = 3.6V at 20mA). These are set-up with 5 LEDs in the MAIN string and 5 LEDs in the SUB string. Alternatively, resistors can be installed in the R1 and R2 pads to make the device a voltage output boost converter for OLED display powering (see Output Voltage Setting (OLED Mode). Please refer to the LM3509 data sheet and applications note.
- Integrated OLED Display Power Supply and LED Driver
- Drives up to 10 LEDs at 30mA
- Drives up to 5 LEDs 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 LEDs
- 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
- Dual Display LCD Backlighting for Portable Applications
- Large Format LCD Backlighting
- OLED Panel Power Supply