APW7062B Ver la hoja de datos (PDF) - Anpec Electronics

Número de pieza

componentes Descripción

Fabricante

APW7062B

Synchronous Buck PWM Controller

Anpec Electronics 

APW7062B

Functional Pin Description

RT (Pin1)

This pin can adjust the switching frequency. Connect

a resistor from RT to GND for increasing the switching

frequency:

FS

=

200kHz

+

4.15 ×106

RT

(RT to GND,FS = 200kHz to 400kHz)

Conversely, connect a resistor from RT to VCC for de-

creasing the switching frequency:

FS

=

200kHz

-

3.51 × 10 7

RT

(RT to VCC,FS = 200kHz to 75kHz)

OCSET (Pin2)

This pin serves two functions: a shutdown control and

the setting of over current limit threshold. Pulling this

pin below 1.27V will shutdown the controller, forcing

the UGATE and LGATE signals to be at 0V.

A resistor (Rocset) connected between this pin and the

drain of the high side MOSFET will determine the over

current limit. An internal 200uA current source will

flow through this resistor, creating a voltage drop,

which will be compared with the voltage across the

high side MOSFET. The threshold of the over current

limit is therefore given by:

( ) IPEAK = IOCSET 200uA R × OCSET

RDS(ON)

To avoid noise interference from switching transient, a

delay time is designed in the OCP comparator.

The over current protection is active only when the

high side MOSFET is turned on longer than 300ns.

SS (Pin3)

Connect a capacitor from the pin to GND to set the

soft-start interval of the converter. An internal 10uA

current source charges this capacitor to 5.8V. The

SS voltage clamps the error amplifier output, and Fig-

ure1 shows the soft-start interval. At t1, the SS volt-

age reaches the valley of the oscillator’s triangle wave.

The PWM comparator starts to generate a PWM sig-

nal to control logic, and the output is rising rapidly.

Until the output is in regulation at t2, the clamp on the

COMP is released. This method provides a rapid and

controlled output voltage rise.

When over current protection occurs, the VOUT is

shutdown, and re-soft-start again, if the over current

condition still exists in soft-start , the VOUT is

shutdowned again, after the SS reaches 4.5V, the SS

is discharged to zero. The soft-start is recurring until

the over current condition is eliminated.

VO L TAGE

VSOFT STAR T

VOSC (M IN)

VSS= 1 .2 V

VO U T

Erro r Am p

Ou tput

t0

t1

t2

t3

TIME

FIGURE1. SOFT-START INTERVAL

I t2

=

CSS

SS

× (VOSC(MIN)+

t1)

= − = × × tSoftStart t3 t2

CSS V OUT SteadyState ∆VOSC

ISS

VIN

Copyright  ANPEC Electronics Corp.

5

Rev. A.3 - Mar., 2005

www.anpec.com.tw

Share Link: