F3
ICE3AS02 / ICE3AS02G / ICE3BS02 / ICE3BS02G
Functional Description
Once the malfunction condition is removed, this block
will then turn back on. The recovery from Auto Restart
Mode does not require disconnecting the SMPS from
the AC line.
VSoftS
max. Startup Phase
When Active Burst Mode is entered, the internal Bias is
switched off in order to reduce the current consumption
to below 1.05mA while keeping the Voltage Reference
active as this is necessary in this mode.
5.4V
4V
3.3
Startup Phase
1V
max. Soft Start Phase
6.5V
DCmax
t
3.25k
DC
1
R
T2
SoftS
DC
2
T3
1V
SoftS
C
SoftS
t1
t2 t
Soft Start
Soft-Start
Comparator
Gate Driver
Figure 6
Startup Phase
C7
&
By means of this extra charge stage, there is no delay
in the beginning of the Startup Phase when there is still
no switching. Furthermore Soft Start is finished at 4V to
have faster the maximum power capability. The duty
cycles DC1 and DC2 are depending on the mains and
the primary inductance of the transformer. The
limitation of the primary current by DC2 is related to
VSoftS = 4V. But DC1 is related to a maximum primary
current which is limited by the internal Current Limiting
with CS = 1V. Therefore the maximum Startup Phase
is divided into a Soft Start Phase until t1 and a phase
from t1 until t2 where maximum power is provided if
demanded by the FB signal.
G7
C2
4V
0.85V
CS
x3.7
PWM OP
Soft Start
Figure 5
At the beginning of the Startup Phase, the IC provides
a Soft Start duration whereby it controls the maximum
primary current by means of a duty cycle limitation. A
signal VSoftS which is generated by the external
capacitor CSofts in combination with the internal pull up
resistor RSoftS, determines the duty cycle until VSoftS
exceeds 4V.
When the Soft Start begins, CSoftS is immediately
charged up to approx. 1V by T2. Therefore the Soft
Start Phase takes place between 1V and 4V. Above
VSoftsS = 4V there is no longer duty cycle limitation
DCmax which is controlled by comparator C7 since
comparator C2 blocks the gate G7 (see Figure 5). The
maximum charge current in the very first stage when
VSoftS is below 1V, is limited to 1.32mA.
Version 1.1
9
21 May 2004
INFINEON [ Infineon ]
