ACT4082A

Rev0, 16-May-08

- 10 -

www.active-semi.com

Copyright © 2008 Active-Semi, Inc.

Active-Semi

Hiccup Mode

If the ACT4082A 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

ACT4082A responds quickly to instantaneous se-

vere overload conditions while providing immunity

to false hiccups that may occur with a heavily

loaded output.

Thermal Shutdown

The ACT4082A 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.