APW7145KA datasheet(13/23 Pages) ANPEC

13 / 23 page

Rev. A.3- Sep., 2008

APW7145

www.anpec.com.tw

Function Description

VIN Power-On-Reset (POR)

The APW7145 keeps monitoring the voltage on the VIN

pin to prevent wrong logic operations which may occur

when VIN voltage is not high enough for the internal con-

trol circuitry to operate. The VIN POR has a rising thresh-

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

During start-up, the VIN voltage must exceed the enable

voltage threshold. Then, the IC starts a start-up process

and ramps up the output voltage to the voltage target.

Digital Soft-Start

The APW7145 has a built-in digital 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 (V

RAMP), connected to one of the positive inputs of

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

reference voltage (0.8V) until the voltage ramp reaches

the reference voltage.

During soft-start without output overvoltage, the APW7145

converter’s sinking capability is disabled until the output

voltage reaches the voltage target.

Digital Soft-Stop

At the moment of shutdown controlled by EN signal,

undervoltage event, or over-temperature protection, the

APW7145 initiates a digital 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 light load.

After the soft-stop interval elapses, the soft-stop process

ends and the the IC turns on the low-side power MOSFET.

Output Undervoltage 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 undervoltage 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 undervoltage comparator has a built-in

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

down caused by noise. The under-voltage protection

works in a hiccup mode without latched shutdown. The

IC will initiate a new soft-start process at the end of the

preceding delay.

Over-Voltage Protection (OVP)

The over-voltage function monitors the output voltage by

FB pin. When the FB voltage increase over 118% 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 high. This

action actively pulls down the output voltage and eventu-

ally attempts to blow the internal bonding wires. As soon

as the output voltage is within regulation, the OVP com-

parator is disengaged. The chip will restore its normal

operation. This OVP scheme only clamps the voltage over-

shoot and does not invert the output voltage when other-

wise activated with a continuously high output from low-

side MOSFET driver - a common problem for OVP

schemes with a latch.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7145. When the junction temperature ex-

ceeds T

J = +150

oC, a thermal sensor turns off the both

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

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

cess and regulate the output voltage again after the junc-

tion temperature cools by 40oC. The OTP is designed

with a 40oC hysteresis to lower the average T

J during

continuous thermal overload conditions, increasing life-

time of the APW7145.

Enable/Shutdown

Driving EN to the ground initiates a soft-stop process

and then places the APW7145 in shutdown. When in

shutdown, after the soft-stop process is completed, the

internal power MOSFETs turns off, all internal circuitry

shuts down and the quiescent supply current reduces to

less than 3mA.

APW7145KA датащи(PDF) 13 Page - Anpec Electronics Coropration

APW7145KA датащи(HTML) 13 Page - Anpec Electronics Coropration

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

датащи скачать

ссылки URL