Active-Semi
Soft-Start
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.
ACT4082A
Frequency Foldback
Rev0, 16-May-08
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 V
IN
< 5.5V
OUT if V
OUT
< 5.5V
D2
1N4148
(Optional)
C3
22nF
D1
B230A
G
5
FB
4
R
FB2
9.53k?
Ω
1%
V
IN
2
C1
10µF
IN
BST
6
ACT4082A
SW
ON
OFF
3
EN
1
L1
4.7µH
C2
22µF
R
FB1
49.9k?
Ω
1%
V
OUT
5V
Innovative Power
TM
-8-
www.active-semi.com
Copyright © 2008 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
