ICE2A0565 Datasheet, PDF (12/36 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V/ 800V CoolMOS

CoolSET™-F2
6.5V
R_FB
Soft-Start Comparator
FB
PWM-Latch
Optocoupler
PWM Comparator
0.8V
PWM OP
Isense
x3.65
Improved
Current Mode
Figure 11 PWM Controlling
3.3
Soft-Start
V_SoftS
5.6V
5.3V
T_Soft-Start
Gate Driver
t
Functional Description
pull-up resistor R_Soft-Start. The Soft-Start-Comparator
compares the voltage at pin SoftS at the negative input
with the ramp signal of the PWM-OP at the positive
input. When Soft-Start voltage V_SoftS is less than
Feedback voltage V_FB the Soft-Start-Comparator limits
the pulse width by resetting the PWM-Latch (see
Figure 12). In addition to Start-Up, Soft-Start is also
activated at each restart attempt during Auto Restart.
By means of the above mentioned C_Soft-Start the Soft-
Start can be defined by the user. The Soft-Start is
finished when V_SoftS exceeds 5.3V. At that time the
Protection Unit is activated by Comparator C4 and
senses the FB by Comparator C3 wether the voltage is
below 4.8V which means that the voltage on the
secondary side of the SMPS is settled. The internal
Zener Diode at SoftS has a clamp voltage of 5.6V to
prevent the internal circuit from saturation (see Figure
13).
5.6V
SoftS
6.5V
Power-Up Reset
R_Soft-Start
Error-Latch
RQ
6.5V
C4
5.3V
G2
SQ
4.8V
R_FB
FB
RQ
C3
Gate
Clock
Driver
SQ
PWM-Latch
Figure 13 Activation of Protection Unit
The Start-Up time T_Start-Up within the converter output
voltage V_OUT is settled must be shorter than the Soft-
Start Phase T_Soft-Start (see Figure 14).
C_{Soft – Start} = _R----_S--_o-^T-_f-_t--^S_–--^o-_S--^f_t-_a^t--_r^–-_t--^S-_×-^t--^a-1-^r--^t_.--6---9-
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 prevents saturation of the transformer
during Start-Up.
t
Figure 12 Soft-Start Phase
The Soft-Start is realized by the internal pull-up resistor
R_Soft-Start and the external Capacitor C_Soft-Start (see
Figure 5). The Soft-Start voltage V_SoftS is generated by
charging the external capacitor C_Soft-Start by the internal
Version 2.6
12
25 Dec 2006