ICE3A1065ELJ Datasheet, PDF (12/29 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V CoolMOS

CoolSET^®-F3
ICE3A1065ELJ
Functional Description
V_SoftS
V_SOFTS32
t_Soft-Start
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
integrated CoolMOS^®, the clamp circuit and the output
overshoot and it helps to prevent saturation of the
transformer during Start-Up.
3.5
PWM Section
Gate
Driver
t
0.75
Oscillator
Duty Cycle
max
PWM Section
t
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).
In addition to Start-Up, Soft-Start is also activated at
each restart attempt during Auto Restart.
V_SoftS
V_SOFTS32
t_Soft-Start
Clock
Frequency
Jitter
Soft Start
Block
Soft Start
Comparator
PWM
Comparator
Current
Limiting
FF1
1
S
Gate Driver
G8
RQ
&
G9
CoolMOS^®
Gate
V_FB
4.0V
V_OUT
V_OUT
t_Start-Up
Figure 13 Start Up Phase
t
Figure 14 PWM Section Block
3.5.1
Oscillator
The oscillator generates a fixed frequency of 100KHz
with frequency jittering of ±4% (which is ±4KHz) at a
jittering period of 4ms.
A capacitor, a current source and a current sink which
t
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
reach a maximum duty cycle limitation of D_max=0.75.
Once the Soft Start period is over and when the IC goes
t ^{into normal operating mode, the switching frequency of}
the clock is varied by the control signal from the Soft
Start block. Then the switching frequency is varied in
range of 100KHz ± 4KHz at period of 4ms.
Version 2.1
12
12 May 2009