AP1520

PWM CONTROL 2A STEP-DOWN CONVERTER

AP1520 Rev. 1

6 of 8

JANUARY 2007

www.diodes.com

Test Circuit

A

FB

VSS

EN

open

open

FB

EN

+

-

OUTPUT

OUTPUT

A

FB

EN

+

-

+

-

V

OUTPUT

OCSET

OCSET

OCSET

Function Description

PWM Control

The AP1520 consists of DC/DC converters that employ a

Pulse-Width Modulation (PWM) system. In converters of the

AP1520, the pulse width varies in a range from 0 to 100%,

according to the load current. The ripple voltage produced by the

switching can easily be removed through a filter because the

switching

frequency

remains

constant.

Therefore,

these

converters provide a low-ripple power over broad ranges of input

voltage and load current.

Under Voltage Lockout

The Under Voltage Lockout circuit of the AP1520 assures

that the high-side MOSFET driver outputs remain in the off state

whenever the supply voltage drops below 3.3V. Normal operation

The current limit threshold is setting by the external

100uA sink current crossing the resistor sets the voltage at the

pin of OCSET. When the PWM voltage is less than the voltage at

OCSET, an over-current condition is triggered.

R

I

R

I

OCSET

OCSET

DS(ON)

LOAD

×

=

×

See above formula for setting the current limit value.