APW7153B datasheet(11/20 Pages) ANPEC

11 / 20 page

Rev. A.6 - Aug., 2012

APW7153/A/B

www.anpec.com.tw

Function Description

VDD and PVDD Power-On-Reset (POR)

The APW7153/A/B keeps monitoring the voltage on VDD

and PVDD pins to prevent wrong logic operations which

may occur when VDD or PVDD voltage is not high enough

for internal control circuitry to operate. The VDD POR ris-

ing threshold is 2.4V (typical) with 0.2V hysteresis and

PVDD POR rising threshold is 1.7V with 0.05V hysteresis.

During start-up, the VDD and PVDD voltage must exceed

the enable voltage threshold. Then, the IC starts a start-

up process and ramps up the output voltage to the volt-

age target.

Output Under-Voltage Protection (UVP)

In the operational process, if a short-circuit occurs, the

output voltage will drop quickly. Before the current-limit

circuit responds, the output voltage will fall out of the re-

quired regulation range. The under-voltage continually

monitors the FB voltage after soft-start is completed. If a

load step is strong enough to pull the output voltage lower

than the under-voltage threshold, the IC shuts down con-

verter’s output.

The under-voltage threshold is 50% of the nominal out-

put voltage. The under-voltage comparator has a built-in

µs noise filter to prevent the chips from wrong UVP shut-

down being caused by noise. APW7153/A/B will be latched

after under-voltage protection.

Over-Voltage Protection (OVP)

The over-voltage function monitors the output voltage by

FB pin. When the FB voltage increases over 125% of the

reference voltage due to the high-side MOSFET failure or

for other reasons, the over-voltage protection compara-

tor will force the low-side MOSFET gate driver to be high.

This action actively pulls down the output voltage and

eventually attempts to blow the internal bonding wires.

As soon as the output voltage is within regulation, the

OVP comparator is disengaged. The chip will restore its

normal operation.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7153/A/B. When the junction temperature

exceeds T

J=+160

oC, a thermal sensor turns off the both

Current-Limit Protection

The APW7153/A/B monitors the output current, flows

through the high-side and low-side power MOSFETs, and

limits the current peak at current-limit level to prevent the

IC from damaging during overload, short-circuit, and over-

voltage conditions. Typical high side power MOSFET cur-

rent-limit is 4.5A, and low side MOSFET current-limit is

1.6A maximum.

power MOSFETs, allowing the devices to cool. The ther-

mal sensor allows the converters to start a start-up pro-

cess and to regulate the output voltage again after the

junction temperature cools by 50oC. The OTP is designed

with a 50oC hysteresis to lower the average T

J during

continuous thermal overload conditions, increasing life-

time of the APW7153/A/B.

Soft-Start

The APW7153/A/B has a built-in soft-start to control the

rise rate of the output voltage and limit the input current

surge during start-up. During soft-start, an internal volt-

age ramp connected to one of the positive inputs of the

error amplifier, rises up from 0V to 0.95V to replace the

reference voltage, V

REF until the voltage ramp reaches the

reference voltage. During soft-start without output over-

voltage, the APW7153/A/B converter’s sinking capability

is disabled until the output voltage reaches the voltage

target.

Soft-Off

At the moment of shutdown controlled by SHDN/RT

signal, under-voltage event or over-temperature

protection, the APW7153/A/B initiates a soft-stop process

to discharge the output voltage in the output capacitors.

Certainly, the load current also discharges the output

voltage. During soft-stop, the internal voltage ramp (V

RAMP)

falls down rises from 0.95V to 0V to replace the reference

voltage. Therefore, the output voltage falls down slowly at

the light load. After the soft-stop interval elapses, the soft-

stop process ends and the IC turns on the low-side power

MOSFET.

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