APW7323KAI-TRG datasheet(12/22 Pages) ANPEC

12 / 22 page

Rev. A.5 - Aug., 2013

APW7323/A

www.anpec.com.tw

Function Description

VCC and VIN Power-On-Reset (POR)

TThe APW7323/A keeps monitoring the voltage on VIN

and VCC pins to prevent wrong logic operations which

may occur when VIN or VCC voltage is not high enough

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

ing threshold is 2.7V (typical) with 0.2V hysteresis and

VIN POR rising threshold is 2.3V with 0.05V hysteresis.

During startup, the VCC and VIN voltage must exceed the

POR threshold. Then the IC starts a starts-up process

and ramps up the output voltage to the voltage 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

converter’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. The APW7323/A 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 comparator

will force the low-side MOSFET gate driver high. This ac-

tion actively pulls down the output voltage and eventually

attempts to blow the internal bonding wires. As soon as

the output voltage is less than 0.2V, the APW7323/A will

be latched off and needs a POR or enable to recover to

normal operation.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7323/A. When the junction temperature

exceeds T

J =160

oC, a thermal sensor turns off the both

power MOSFETs, allowing the devices to cool.

Current-Limit Protection

The APW7323 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 4.8A, and low side MOSFET current limit is 1.

9A.

Soft-Start

The APW7323/A 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 voltage ramp

connected to one of the positive inputs of the error

amplifier, rises up from 0V to 0.95V to replace the refer-

ence voltage (0.8V) until the voltage ramp reaches the

reference voltage. During soft-start without output over-

voltage, the APW7323/A converter’s sinking capability is

disabled until the output voltage reaches the voltage target.

Soft-Stop

At the moment of shutdown controlled by EN signal, un-

der-voltage event or over-temperature protection, the

APW7323/A 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 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.

Enable and Shutdown

Driving EN to ground places the APW7323/A in shutdown.

In shutdown mode, the internal power MOSFETs turns

off, all internal circuitry shuts down and the quiescent

supply current reduces to less than 20

µA.

The thermal sensor allows the converters to start a start-

up process and to regulate the output voltage again after

the junction temperature cools by 50oC. The OTP is de-

signed with a 50oC hysteresis to lower the average T

during continuous thermal overload conditions, increas-

ing lifetime of the APW7323/A.

APW7323KAI-TRG Datasheet(PDF) 12 Page - Anpec Electronics Coropration

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