APW7137 Ver la hoja de datos (PDF) - Anpec Electronics

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APW7137

1MHz, High Efficiency, Step-Up Converter with Internal FET Switch

Anpec Electronics 

APW7137

Function Description

Main Control Loop

The APW7137 is a constant frequency and current-mode

switching regulator. In normal operation, the internal N-

channel power MOSFET is turned on each cycle when the

oscillator sets an internal RS latch, and then 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 node which is

the output of the error amplifier (EAMP). An external resis-

tive divider connected between VOUT and ground allows

the EAMP to receive an output feedback voltage V at FB

FB

pin. When the load current increases, it causes a slightly

to decrease in VFB associated with the 1.23V reference,

which in turn, it causes the COMP voltage to increase

until the average inductor current matches the new load

current.

VIN Under-Voltage Lockout (UVLO)

The Under-Voltage Lockout (UVLO) circuit compares the

input voltage at VIN with the UVLO threshold to ensure

the input voltage is high enough for reliable operation.

The 100mV (typ) hysteresis prevents supply transients

from causing a restart. Once the input voltage exceeds

the UVLO rising threshold, startup begins. When the in-

put voltage falls below the UVLO falling threshold, the

controller turns off the converter.

Soft-Start

The APW7137 has a built-in soft-start to control the output

voltage rise during start-up. During soft-start, an internal

ramp voltage, connected to the one of the positive inputs

of the error amplifier, raises up to replace the reference

voltage (1.23V typical) until the ramp voltage reaches the

reference voltage.

Current-Limit Protection

The APW7137 monitors the inductor current, flows through

the N-channel MOSFET, and limits the current peak at

current-limit level to prevent loads and the APW7137 from

damaging during overload or short-circuit conditions.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7137. When the junction temperature ex-

ceeds 150oC, a thermal sensor turns off the power

MOSFET allowing the devices to cool. The thermal sen-

sor allows the converters to start a soft-start process and

regulates the output voltage again after the junction tem-

perature cools by 40oC. The OTP is designed with a 40oC

hysteresis to lower the average Junction Temperature

(TJ) during continuous thermal overload conditions in-

creasing the lifetime of the device.

Enable/Shutdown

Driving EN to the ground places the APW7137 in shut-

down mode. When in shutdown, the internal power

MOSFET turns off, all internal circuitry shuts down, and

the quiescent supply current reduces to 1µA maximum.

Copyright © ANPEC Electronics Corp.

12

Rev. A.4 - Oct., 2008

www.anpec.com.tw

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