ICE3A1065ELJ Datasheet, PDF (11/29 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V CoolMOS

3.4
Startup Phase
Soft Start counter
CoolSET^®-F3
ICE3A1065ELJ
Functional Description
SoftS
Soft Start
Soft Start
Soft-Start
Comparator
Gate Driver
C7
&
G7
V _SoftS
V_SoftS2
V_SoftS1
0.6V
x3.2
PWM OP
Figure 10 Soft Start Phase
CS
5V
SoftS
R _{S o ftS}
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
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.
Soft Start ^{32I 8I 4I 2I I}
Counter
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.
Version 2.1
11
12 May 2009