SLVSFM1 March 2021 TPS62902
The TPS62902 can be used as a power supply for power LEDs. The FB pin can be easily set to lower values than nominal by using the SS/TR pin. With that, the voltage drop on the sense resistor is low to avoid excessive power loss. Since this pin provides 2.5 µA, the feedback pin voltage can be adjusted by an external resistor per Equation 19. This drop, proportional to the LED current, is used to regulate the output voltage (anode voltage) to a proper level to drive the LED. Both analog and PWM dimming are supported with the TPS62902. Figure 8-80 shows an application circuit, tested with analog dimming.
The resistor at SS/TR defines the FB voltage. It is set to 304 mV by RSS/TR = R4 = 162 kΩ using Equation 19. This cuts the losses on R4 to half from the nominal 0.6 V of feedback voltage while it still provides good accuracy.
The device now supplies a constant current set by resistor R2 from FB/VSET to GND. The minimum input voltage has to be rated according the forward voltage needed by the LED used. More information is available in SLVA451.