F3 PWM controller
ICE3BS03LJG
Functional Description
failure such as short winding or short diode, C10 is no generated which prevents the system to enter Auto
longer able to limit the CS signal at 1.06V. Instead the Restart Mode due to large load jumps.
comparator C11 detects the peak current voltage >
1.66V and enters the Latched Off Mode immediately in
order to keep the SMPS in a safe stage.
In case of VCC undervoltage, the IC enters into the
Auto Restart Mode and starts a new startup cycle.
Short Optocoupler also leads to VCC undervoltage as
there is no self supply after activating the internal
reference and bias.
In contrast to the Latched Off Mode, there is always a
Startup Phase with switching cycles in Auto Restart
Mode. After this Start Up Phase, the conditions are
again checked whether the failure mode is still present.
Normal operation is resumed once the failure mode is
removed that had caused the Auto Restart Mode.
In case the pre-defined Latch Off features are not
sufficient, there is a customer defined external Latch
Enable feature. The Latch Off Mode can be triggered
by pulling down the BL pin to < 0.25V. It can simply add
a trigger signal to the base of the externally added
transistor, TLE at the BL pin. To ensure this latch
function will not be mis-triggered during start up, a 1ms
delay time is implemented to blank the unstable signal.
3.7.3.2
Auto Restart Mode
BL
5.0V
CBK
#
IBK
0.9V
1
S1
G2
C3
C4
Spike
Blanking
30us
4.0V
&
20ms
Blanking
Time
G5
Auto
Restart
Mode
4.0V
FB
Control Unit
Figure 27
Auto Restart Mode
In case of Overload or Open Loop, the FB exceeds
4.0V which will be observed by comparator C4. Then
the internal blanking counter starts to count. When it
reaches 20ms, the switch S1 is released. Then the
clamped voltage 0.9V at VBL can increase. When there
is no external capacitor CBK connected, the VBL will
reach 4.0V immediately. When both the input signals at
AND gate G5 is positive, the Auto-Restart Mode will be
activated after the extra spike blanking time of 30us is
elapsed. However, when an extra blanking time is
needed, it can be achieved by adding an external
capacitor, CBK. A constant current source of IBK will start
to charge the capacitor CBK from 0.9V to 4.0V after the
switch S1 is released. The charging time from 0.9V to
4.0V are the extendable blanking time. If CBK is 0.22uF
and IBK is 13uA, the extendable blanking time is around
52ms and the total blanking time is 72ms. In combining
the FB and blanking time, there is a blanking window
Version 2.0
17
6 Dec 2007
INFINEON [ Infineon ]
