ACT4088
Rev 2, 15-Nov-12
Soft-Start
Frequency Foldback
The ACT4088 provides an internal soft-start fea-
ture, which ramps the output voltage and output
current are from 0 to the full value over 0.5 millisec-
onds. This feature prevents output voltage over-
shoot at light loads as well as to prevent large in-
rush currents upon startup. The soft-start circuitry is
internally reset anytime the IC is disabled using the
EN pin, as well as if the IC reaches hiccup mode or
thermal shutdown. In all of these cases, soft-start
provides a smooth, controlled restart after the fault
is removed.
The voltage at FB is monitored by a comparator to
detect an extreme output overload condition. If the
voltage at the FB pin falls to below 0.3V, the inter-
nal oscillator slows to a decreased frequency of
467kHz, 33% of the nominal value. This prevents
the inductor current from rising excessively during a
dead-short condition, potentially resulting in induc-
tor saturation.
Figure 2:
ACT4088 Typical 5V/1.5A Output Application
Innovative PowerTM
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