AP1580

PWM CONTROL 3A STEP-DOWN CONVERTER

AP1580 Rev. 1

7 of 9

JANUARY 2007

www.diodes.com

Test Circuit

A

FB

Vcc

GND

EN

open

open

FB

Vcc

GND

EN

+

-

OUTPUT

OUTPUT

A

FB

Vcc

GND

EN

+

-

+

-

V

OUTPUT

Vboost

open

Vboost

Vboost

Enable function test

Feedback function test

Operation function test

220uF

0.1uF

33uH

470uF

680 ohm

130 ohm

Function Description

PWM Control

The AP1580 consists of DC/DC converters that employ a

pulse-width modulation (PWM) system. The PWM controller is

internally clocked by a fixed 300KHz oscillator.

In converters of the AP1580, the pulse width varies in a range

from 0 to 90%, 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.

Enable Control

This input provides an electrical ON/OFF control of the power

supply. Connecting this pin to ground or to any voltage less than

0.8V will completely turn OFF the regulator. The current drain

from the input supply when OFF is only 2uA.

C BOOST

A capacitor must be connected from pin 3 to the switch output,

pin 4. This capacitor boosts the gate drive to the internal

MOSFET above Vin to fully turn it ON. This minimizes conduction

losses in the power switch to maintain high efficiency. The

recommended value for C Boost is 0.1uF.

FEEDBACK

This is the input to a two-stage high gain amplifier, which drivers

the PWM controller. It is necessary to connect pin 2 to the actual

output of the power supply to set the DC output voltage. Two

external resistors are required to set the DC output voltage. For

stable operation of the power supply, it is important to prevent

coupling of any inductor flux to the feedback input.

Current Limit

The current limit threshold is set by the internal circuit that

minimum switching current is 4A. The output voltage will be

reduced immediately and switching frequency will be dropped to

30KHz when switching current over limit threshold.

Thermal shutdown

The thermal shutdown temperature depends on internal junction

temperature. When junction temperature rises up to 140℃, the

device will be shut down and it will be recovered after

temperature reduced lower than 90℃.