F3 PWM controller
ICE3BS03LJG
Functional Description
is a built-in function and it is controlled by an internal
counter.
5V
Soft-Start Comparator
RFB
FB
PWM-Latch
C8
PWM Comparator
0.6V
VSoftS
Optocoupler
PWM OP
CS
VSoftS2
VSoftS1
X3.2
Improved
Current Mode
Figure 10
Soft Start Phase
Figure 8
PWM Controlling
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 S tart counter
5V
SoftS
Soft Start
RSoftS
SoftS
Soft Start
Soft-Start
C om parator
G ate D river
C 7
&
G 7
32I
4I
8I
2I
I
Soft Start
Counter
0.6V
C S
x3.2
PW M O P
Figure 11
Soft Start Circuit
After the IC is switched on, the VSFOFTS 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
Figure 9
Soft Start
In the Startup Phase, the IC provides a Soft Start
period to control the maximum primary current by
means of a duty cycle limitation. The Soft Start function
Version 2.0
10
6 Dec 2007
INFINEON [ Infineon ]
