ACT4088
Rev PrA, 24-Jul-07
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.
Innovative Products. Active Solutions.
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