The first step is to know your optical light output requirements which will require you to choose the right type and number of LEDs. LEDs come in many shapes and sizes; and for this example we will choose a design that requires 3 white LEDs. We have chosen a type of LED which gives our required illumination with 300 mA forward drive current. The ZXLD1350 can drive LEDs with a forward current up to 350 mA which is typical for a 1 W LED. The combined forward volt drop of the LEDs sets the minimum input voltage. Typical values are 3.6 V but this value changes with the LED type and temperature; so be sure to use the maximum voltage when setting the input voltage. Using this value with 3 LEDs connected in series sets a voltage of 10.8 across the LEDs. There is also a number of other volt drops across the sense resistor R sense and the inductor. So using the equation VIN is greater than (VLED multiplied by No LEDS +1.5 V) sets the minimum input to 12.3 V.