Illustrate:
The LM3509 current mode boost converter provides two separate outputs. The first output (master) is a constant sink current to drive the series white LED. The second outut (SUB/FB) is a configurable series of white LEDs biased as a constant sink or constant output voltage feedback pin set to power the OLED panel.
When configured with a dual-output white LED bias supply, the LM3509 adaptively adjusts the supply voltage of the LED string to maximize efficiency and ensure current sink regulation is maintained. The maximum current for each output is through an external low-power resistor. An I2 CCompatible interface, independently adjustable LED current, both step current output from 0 to a maximum of 32 exponents. When configured as a white LED + OLED bias supply, the LM3509 can independently drive a string of 5 white LEDs and OLED panels to provide a constant output voltage to 21V.
The output overvoltage protection function is turned off if the above allows the use of small low voltage outputscapacitorThe 21V, V OUT rises. The LM3509 is available in a small 10-pin thermally enhanced LLP package that operates over the -40°C to +85°C temperature range.
The LM3509SD evaluation board is set up to drive 2 strings of 5 white LEDs (Osram, LW_M67C, at 20mA).targetV F = 3.6V）。 These set the main string of 5 LEDs and the 5 LEDs in the small string. In addition, resistors can be mounted on the R1 and R2 pads to boost the voltage output of the OLED device to the converter and display the power supply (output voltage sets OLED (mode). Refer to the LM3509 datasheet and application note.
Peculiarity:
- Integrated OLED display power supply and LED driver
- Drive up to 10 LEDs at 30 mA
- LED drivers at 20mA and available up to 40mA to 21V
- More than 90% efficiency
- 32 exponential dimming steps
- 0.15% accurate current matching between strings
- Internal soft-start limits inrush current
- The LED's True Shutdown function is isolated
- Input voltage range of 2.7V to 5.5V
- 21V overvoltage protection
- 1.27MHz fixed frequency operation
- Low Profile 10-Pin LLP Package (3 × 3 ×0.8mm)
- Universal I/O
- Active low hardware reset
Scope of application:
- Backlight in dual-display portable applications
- Large format LCD backlight
- OLED panel power supply