APW7089 datasheet(16/24 Pages) ANPEC

16 / 24 page

Rev. A.1 - Jan., 2012

APW7089

www.anpec.com.tw

Function Description (Cont.)

put voltage. The under-voltage 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

preceeding delay.

Over-Temperature Protection (OTP)

The over-temperature circuit limits the junction tempera-

ture of the APW7089. When the junction temperature ex-

ceeds T

J = +150

oC, a thermal sensor turns off the power

MOSFET, allowing the devices to cool. The thermal sensor

allows the converter to start a start-up process and

regulate the output voltage again after the junction

temperature is cooled by 50oC. The OTP is designed

with a 50oC hysteresis to lower the average T

J during con-

tinuous thermal overload conditions, increasing lifetime

of the IC.

Enable/Shutdown

Driving EN to ground places the APW7089 in shutdown.

When in shutdown, the internal power MOSFET turns off,

all internal circuitry shuts down and the quiescent supply

current of VIN reduces to <1

µA (typical).

Current-Limit Protection

The APW7089 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

damages during overload or short-circuit conditions.

Frequency Foldback

When the output is shortened to 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

frequency will gradually increase to its designed rate

when the feedback voltage on FB again approaches 0.8V.

Output Under-Voltage Protection (Cont.)

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