CoolSET®-F3R
ICE3BR0665JF
Functional Description
When the VVCC exceeds the on-threshold voltage, the
IC starts the Soft Start mode (see Figure 10).
3.4
Startup Phase
The function is realized by an internal Soft Start
resistor, an current sink and a counter. And the
amplitude of the current sink is controlled by the
counter (see Figure 11).
Soft Start counter
SoftS
Soft Start
Soft Start
5V
RSoftS
SoftS
Soft-Start
C om parator
G ate D river
C 7
&
G 7
32I
4I
8I
2I
I
Soft Start
Counter
0.68V
C S
x3.3
PW M O P
Figure 9
Soft Start
Figure 11
Soft Start Circuit
In the Startup Phase, the IC provides a Soft Start
period to control the 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.
After the IC is switched on, the VSOFTS 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
increases gradually. The Soft Start will be finished in
20ms (tSoft-Start) after the IC is switched on. At the end of
the Soft Start period, the current sink is switched off.
.
VSoftS
tSoft-Start
VSOFTS32
VSoftS
t
VSoftS2
VSoftS1
Gate
Driver
t
Figure 10
Soft Start Phase
Figure 12 Gate drive signal under Soft-Start Phase
Version 2.0
11
11 Sep 2008
INFINEON [ Infineon ]
