APW7304 查看數據表（PDF） - Anpec Electronics

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APW7304

4A 24V 340kHz synchronous Buck Converter

Anpec Electronics 

APW7304

Function Description

Main Control Loop

The APW7304 is a constant frequency current mode

switching regulator. During normal operation, the inter-

nal N-channel power MOSFET is turned on each cycle

when the oscillator sets an internal RS latch and would

be turned off when an internal current comparator (ICMP)

resets the latch. The peak inductor current at which ICMP

resets the RS latch is controlled by the voltage on the

COMP pin, 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 slight decrease in VFB relative to

the 0.8V reference, which in turn causes the COMP volt-

age to increase until the average inductor current matches

the new load current.

VIN Power-On-Reset (POR) and EN Under-voltage

Lockout

The APW7304 keep monitoring the voltage on VIN pin to

prevent wrong logic operations which may occur when

VIN voltage is not high enough for the internal control

circuitry to operate. The VIN POR has a rising threshold

of 4.1V (typical) with 0.5V of hysteresis.

An external under-voltage lockout (UVLO) is sensed at

the EN pin. The EN UVLO has a rising threshold of 2.5V

with 0.2V of hysteresis. The EN pin should be connected

a resistor divider from VIN to EN.

After the VIN and EN voltages exceed their respective

voltage thresholds, the IC starts a start-up process and

then ramps up the output voltage to the setting of output

voltage.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7304. When the junction temperature ex-

ceeds TJ = +160oC, a thermal sensor turns off the power

MOSFET, allowing the devices to cool. The thermal sen-

sor allows the converter to start a start-up process and

regulate the output voltage again after the junction tem-

perature cools by 50oC.

The OTP is designed with a 50oC hysteresis to lower the

average TJ during continuous thermal overload conditions,

increasing lifetime of the lC.

Enable / Shutdown

Driving EN to ground places the APW7304 in shutdown.

When in shutdown, the internal power MOSFET turns off,

all internal circuitry shuts down.

Current-Limit Protection

The APW7304 monitors the output current, flowing

through the N-Channel power MOSFET, and limits the

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

voltage conditions.

Frequency Foldback

The foldback frequency is controlled by the FB voltage.

When the FB pin voltage is under 0.6V, the frequency of

the oscillator will be reduced to 110kHz. This lower fre-

quency allows the inductor current to safely discharge,

thereby preventing current runaway. The oscillator’s fre-

quency will switch to its designed rate when the feedback

voltage on FB rises above the rising frequency foldback

threshold (0.6V, typical) again.

Soft-Start

The APW7304 provides the programmed soft-start func-

tion to limit the inrush current. The soft-start time can be

programmed by the external capacitor between SS and

GND. Typical charge current is 6µA, and the soft-start

time is 15ms with 0.1µF capacitor.

Boostrap Capacitor

The APW7304 is a N-channel MOSFET step down

converter. The MOSFET requires a gate voltage that is

higher than input voltage, thus a boost capacitor should

be connected between LX and BS pins to drive the gate of

the N-channel MOSFET. Typical boostrap capacitor value

is from 10nF to 100nF.

Copyright © ANPEC Electronics Corp.

12

Rev. A.3 - Apr., 2013

www.anpec.com.tw

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