APW7176A 查看數據表（PDF） - Anpec Electronics

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APW7176A

Dual 1.5MHz, 1A Synchronous Step-Down Converter

Anpec Electronics 

APW7176A

Function Description

Main Control Loop

The APW7176A has dual independent constant frequency,

current-mode PWM step-down converters. During nor-

mal operation, the internal P-channel power MOSFET is

turned on each cycle when the oscillator sets an internal

RS latch and is turned off when an internal comparator

(ICMP) resets the latch. The peak inductor current at which

ICMP resets the RS latch is controlled by the voltage on

the COMP, which is the output of the error amplifier

(EAMP). An external resistive divider connected between

VOUT and ground allows the EAMP to receive an output

feedback voltage VFB at FB pin. When the load current

increases, it causes a slightly decrease in V associated

FB

with the 0.6V reference, which in turn causes the COMP

voltage to increase until the average inductor current

matches the new load current.

Junction Temperature (TJ) during continuous thermal

overload conditions, increasing the lifetime of the device.

Enable/Shutdown

For each channel, driving EN to the ground places the

channel in shutdown mode. When in shutdown, the inter-

nal power MOSFETs are turned off, all internal circuitry

shuts down, and the quiescent supply current reduces to

1µA maximally.

Soft-Start

Each channel in the APW7176A has a built-in soft-start to

control the output voltage rise during start-up. During soft-

start, an internal ramp, connected to the one of the posi-

tive inputs of the error amplifier, raise up to replace the

reference voltage (0.6V typical) until the ramp voltage

reaches the reference voltage.

Short Circuit Protection

For each channel, when the output is shortened to the

ground, the frequency of the oscillator will be reduced to

210kHz. This lower frequency allows the inductor current

to safely discharge, thereby preventing current runaway.

The oscillator’s frequency will gradually increase to its

designed rate when the feedback voltage on the FB again

approaches 0.6V.

Over-Temperature Protection (OTP)

For each channel, the over-temperature circuit limits the

junction temperature of the APW7176A. When the junc-

tion temperature exceeds 150oC, a thermal sensor turns

off the power MOSFETs, allowing the channels to cool

down. The thermal sensor allows the converter to start a

soft-start process and to regulate the output voltage again

after the junction temperature cools by 40οC. The OTP is

designed with a 40οC hysteresis to lower the average

Copyright © ANPEC Electronics Corp.

8

Rev. A.1 - Oct., 2012

www.anpec.com.tw

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