ACT4088

Rev 1, 14-Feb-11

- 10 -

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Copyright © 2011 Active-Semi, Inc.

Hiccup Mode

If the ACT4088 transitions from normal operation to

a severe overload condition (the voltage at FB falls

below 0.3V), the controller automatically enters

"Hiccup Mode" to provide maximum protection to

the system. In hiccup mode, the IC stops switching,

clears the soft-start circuitry, then attempts to re-

start. If the overload condition has been removed,

the IC will start up normally and continue regulating.

In the case of a sustained overload, however, the

IC will attempt to regulate for a period of time equal

to 3x the soft-start period (1.5ms). If the overload

condition persists until the end of this period, the IC

will begin another hiccup cycle. This hiccup-mode

control scheme minimizes power dissipation during

severe overload conditions, and ensures that the

ACT4088 responds quickly to instantaneous severe

overload conditions while providing immunity to

false hiccups that may occur with a heavily loaded

output.

Thermal Shutdown

The ACT4088 automatically turns off when the IC

junction temperature exceeds 160°C, and re-

enables when the IC junction temperature drops by

10°C (typ).

PC Board Layout

The high current paths at G, IN and SW should be

placed very close to the device with short, direct

and wide traces. The input capacitor needs to be as

close as possible to the IN and G pins. The external

feedback resistors should be placed next to the FB

pin. Keep the switch node traces short and away

from the feedback network and use shielded

inductors.