The TPS62140 can be used as a power supply for power LEDs. The FB pin can be easily set down 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. Because this pin provides 2.5 µA, the feedback pin voltage can be adjusted by an external resistor per Equation 15. 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 TPS62140. Figure 9-40 shows an application circuit, tested with analog dimming:

Figure 9-40 Single Power LED Supply

The resistor at SS/TR sets the FB voltage to a level of about 300 mV and is calculated from Equation 15.

Equation 15.

The device now supplies a constant current, set by the resistor at the FB pin, by regulating the output voltage accordingly. The minimum input voltage must be rated according to the forward voltage needed by the LED used. More information is available in the application note Step-Down LED Driver With Dimming With the TPS621-Family and TPS821-Family Application Report.