Preliminary

TTP933

2013/08/23

Page：21—25

Ver.：1.2

Where

L is the coil inductance

rL is the coil resistance

Iavg is the required LED current

∆I is the coil peak-peak ripple current {Internally set to 0.3 x Iavg}

Diode selection :

For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance

Schottky diode with low reverse leakage at the maximum operating voltage and temperature.

They also provide better efficiency than silicon diodes, due to a combination of lower forward

voltage and reduced recovery time. It is important to select parts with a peak current rating above

the peak coil current and a continuous current rating higher than the maximum output load current. It

is very important to consider the reverse leakage of the diode when operating above 85°C. Excess

leakage will increase the power dissipation in the device and if close to the load may create a thermal

runaway condition. The higher forward voltage and overshoot due to reverse recovery time in silicon

diodes will increase the peak voltage on the SW output. If a silicon diode is used, care should be taken

to ensure that the total voltage appearing on the SW pin including supply ripple, does not exceed the

specified maximum value.