ICE2AS01_06 Datasheet, PDF (9/24 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller

ICE2AS01/S01G
ICE2BS01/S01G
Functional Description
6.5V
R_FB
Soft-Start Comparator
FB
PWM-Latch
Optocoupler
PWM Comparator
0.8V
PWM OP
Isense
x3.65
Improved
Current Mode
Figure 8 PWM Controlling
3.3
Soft-Start
V_SoftS
5.6V
5.3V
T_Soft-Start
Gate Driver
t
pullup 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 reseting the PWM-Latch (see Figure
9). 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 with
breakthrough voltage of 5.6V is to prevent the internal
circuit from saturation (see Figure 10).
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 10 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 11).
C _{Soft − Start}
=
T_{Soft − Start}
R _{Soft − Start} × 1,69
By means of Soft-Start there is an effective
minimization of current and voltage stresses on the
external Power Switch, the clamp circuit and the output
overshoot and prevents saturation of the transformer
during Start-Up.
t
Figure 9 Soft-Start Phase
The Soft-Start is realized by the internal pullup resistor
R_Soft-Start and the external Capacitor C_Soft-Start (see
Figure 2). The Soft-Start voltage V_SoftS is generated by
charging the external capacitor C_Soft-Start by the internal
Datasheet
9
Preliminary Data
30 Jun 2006