APW7083 datasheet(14/22 Pages) ANPEC

14 / 22 page

Rev. A.5 - Sep., 2011

APW7083

www.anpec.com.tw

Function Description (Cont.)

Output Under-Voltage Protection (Cont.)

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 70%

of the nominal output voltage. The under-voltage com-

parator has a built-in 2

µs noise filter to prevent the chips

from wrong UVP shutdown 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 proceeding delay.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7083. When the junction temperature ex-

ceeds T

J = +150

οC, 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 50οC. The OTP is designed with a 50οC

hysteresis to lower the average T

J during continuous ther-

mal overload conditions, increasing lifetime of the IC.

Over-Voltage Protection

The over-voltage function monitors the output voltage by

FB pin. The FB voltage should increase over 118% 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. As soon as the output voltage is within regulation,

the OVP comparator is disengaged. The chips will re-

store its normal operation. This OVP scheme only clamps

the voltage overshoot, and does not invert the output volt-

age when otherwise activated with a continuously high

output from low-side MOSFET driver - a common prob-

lem for OVP schemes with a latch.

Current-Limit Protection

The APW7083 monitors the output current, flowing through

the P-channel power MOSFET, and limits the current peak

at current-limit level to prevent loads and the IC from dam-

ages during overload or short-circuit conditions.

Frequency Foldback

When the output is shortened to the ground, the frequency

of the oscillator will be reduced to about 80kHz. This lower

frequency allows the inductor current to safely discharge,

thereby preventing current runaway. The oscillator’s fre-

quency will gradually increase to its designed rate when

the feedback voltage on FB approaches 0.8V again.

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