FP7151

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Rev. 0.63

9/13

Application Information

Setting the LED Current

pin. To set the LED current according to the following equation:

RS

0.1

=

ILED

For RS=0.33Ω, the LED current is set to 300mA

Shutdown Mode

Taking the ADJ pin to a voltage below 0.2V will turn off the output and the supply current will fall

to a low standby level of 15μA nominal.

Soft Start

The voltage on the ADJ pin is the inductor current reference. An external capacitor from the

capacitor from 0V to 1.25V to fulfill soft-start function.

Capacitor selection

A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears

in series with the supply source impedance and lowers overall efficiency. This capacitor has to supply

the relatively high peak current to the coil and smooth the current ripple on the input supply. A minimum

value of 4.7uF is acceptable if the input source is close to the device, but higher values will improve

performance at lower input voltages, especially when the source impedance is high. The input

capacitor should be placed as close as possible to the IC.

For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better

dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this

application and should not be used.

Reducing output ripple

Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor