ICE3GS03LJG Datasheet, PDF (11/25 Pages) Infineon Technologies AG – Of f-Line SMPS Current Mode Controller wi th integrated 500V Startup Cell

F3 PWM controller
ICE3GS03LJG
Functional Description
decrease gradually and the duty ratio of the gate drive
increases gradually. The Soft Start will be finished in
10ms (t_Soft-Start) after the IC is switched on. At the end of
the Soft Start period, the current sink is switched off.
V_SoftS
V_SOFTS32
t_Soft-Start
In addition to Start-Up, Soft-Start is also activated at
each restart attempt during Auto Restart.
The Start-Up time t_Start-Up before the converter output
voltage V_OUT is settled, must be shorter than the Soft-
Start Phase t_Soft-Start (see Figure 13).
By means of Soft-Start there is an effective
minimization of current and voltage stresses on the
external power MOSFET, the clamp circuit and the
output overshoot and it helps to prevent saturation of
the transformer during Start-Up.
Gate
Driver
3.5
PWM Section
0.75
t
Oscillator
Duty Cycle
max
Clock
Frequency
t
Jitter
PWM Section
Figure 12 Gate drive signal under Soft-Start Phase
Within the soft start period, the duty cycle is increasing
from zero to maximum gradually (see Figure 12).
V_SoftS
V_SOFTS32
t_Soft-Start
Soft Start
Block
Soft Start
Comparator
PWM
Comparator
Current
Limiting
FF1
1S
Gate Driver
G8
RQ
&
G9
V_FB
4.2V
V_OUT
V_OUT
t_Start-Up
Figure 13 Start Up Phase
t
Figure 14 PWM Section Block
Gate
3.5.1
Oscillator
The oscillator generates a fixed frequency of 130kHz
with frequency jittering of ±4% (which is ±5.2kHz) at a
t
jittering period of 4ms.
A capacitor, a current source and a current sink which
determine the frequency are integrated. The charging
and discharging current of the implemented oscillator
capacitor are internally trimmed, in order to achieve a
very accurate switching frequency. The ratio of
controlled charge to discharge current is adjusted to
t
reach a maximum duty cycle limitation of D_max=0.75.
Once the Soft Start period is over and when the IC goes
into normal operating mode, the switching frequency of
the clock is varied by the control signal from the Soft
Version 2.0
11
1 Nov 2010