Datasheet

CoolSET
®
-F3
ICE3A1065ELJ
Functional Description
Version 2.3 11 19 Nov 2012
3.4 Startup Phase
Soft-Start
Comparator
Soft Start
&
G7
C7
Gate Driver
0.6V
x3.2
PWM OP
CS
Soft Start counter
Soft Start
Soft Start finish
SoftS
Figure 9 Soft Start
In the Startup Phase, the IC provides a Soft Start
per
iod to control the maximum primary current by
means of a duty cycle limitation. The Soft Start function
is a built-in function and it is controlled by an internal
counter.
When the V
VCC
exceeds the on-threshold voltage, the
IC starts the Soft Start mode. The function is realized
by an internal Soft Start resistor, a current sink and a
counter. And the amplitude of the current sink is
controlled by the counter.
V
SoftS
V
SoftS2
V
SoftS1
Figure 10 Soft Start Phase
5V
R
SoftS
Soft Start
Counter
I
2I
4I
SoftS
8I
32I
Figure 11 Soft Start Circuit
After the IC is switched on, the V
SoftS
voltage is
controlled such that the voltage is increased step-
wisely (32 steps) with the increase of the counts. The
Soft Start counter would send a signal to the current
sink control in every 600us such that the current sink
decrease gradually and the duty ratio of the gate drive
increase gradually. The Soft Start will be finished in
20ms after the IC is switched on. At the end of the Soft
Start period, the current sink is switched off.