NCL30160

http://onsemi.com

8

L

DI

forward voltage of the catch diode.

The switching frequency can then be approximated from

the following:

1

Higher values of inductance lead to slower rates of rise

and fall of the output current. This allows for smaller

discrepancies between the expected and actual output

current ripple due to propagation delays between sensing at

the CS pin and the turning on and off of the power MOSFET.

However, the inductor value should be chosen such that the

peak output current value does not exceed the rated

saturation current of the inductor.

Catch Diode Selection

The catch diode needs to be selected such that average

current through the diode does not exceed the rated average

forward current of the diode. The average current through

the diode can be calculated as:

It is also important to select a diode that is capable of

withstanding the peak reverse voltage it will see in the

application. It is recommended to select a diode with a rated

reverse voltage greater than VIN. It is also recommended to

use a low-capacitance Schottky diode for better efficiency

performance.

Selecting The Off-Time Setting Resistor

NCL30160 with the initial time duration that the MOSFET

is turned off when the switching operation begins. During

subsequent switching cycles, the voltage at the CS pin is

sensed every time the MOSFET is turned on, and the

off-time will be adjusted depending on how much of a

discrepancy exists between the sensed value and the CS

using the following equation:

switching operation, calculated in the Inductor Selection

section above.

Input Capacitor

A decoupling capacitor from VIN to ground should be

used to provide the current needed when the power

MOSFET turns on. A 4.7

mF ceramic capacitor is

recommended.