ACT4082A
Active- Semi
Rev0, 16-May-08
Soft-Start
Frequency Foldback
The ACT4082A 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:
ACT4082A Typical 5V/1.2A Output Application
Optional Connection:
IN if VIN < 5.5V
OUT if VOUT < 5.5V
D2
1N4148
(Optional)
6
2
VIN
IN
BST
C1
10µF
C3
22nF
L1
4.7µH
1
VOUT
5V
ACT4082A
SW
FB
D1
B230A
C2
22µF
3
ON
OFF
EN
RFB1
4
G
5
49.9kꢀ?
1%
9.53kꢀ?
1%
RFB2
Innovative PowerTM
- 8 -
www.active-semi.com
Copyright © 2008 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
