F3
ICE3AS02 / ICE3AS02G / ICE3BS02 / ICE3BS02G
Functional Description
Once the Auto Restart Mode is entered, the internal
Voltage Reference is switched off in order to reduce the
current consumption of the IC as much as possible. In
this mode, the average current consumption is only
300µA as the only working block is the Undervoltage
Lockout(UVLO) which controls the Startup Cell by
switching on/off at VVCCon/VVCCoff
.
As there is no longer a self supply by the auxiliary
winding, VCC starts to drop. The UVLO switches on the
integrated Startup Cell when VCC falls below 8.5V. It
will continue to charge VCC up to 15V whereby it is
switched off again and the IC enters into the Start Up
Phase.
As long as all fault conditions have been removed, the
IC will automaticlally power up as usual with switching
cycle at the GATE output after Soft Start duration. Thus
the name Auto Restart Mode.
Other fault detections which are active in normal
operation is the sensing for Overload, Open Loop and
VCC undervoltage conditions. In the first 2 cases, FB
will rise above 4.8V which will be observed by C4. At
this time, S1 is released such that VSoftS can rise from
its earlier clamp voltage of 4.4V. If VSoftS exceeds 5.4V
which is observed by C3, Auto Restart Mode is entered
as both inputs of the gate G5 are high.
This charging of the Soft Start capacitor from 4.4V to
5.4V defines a blanking window which prevents the
system from entering into Auto Restart Mode un-
intentionally during large load jumps. In this event, FB
will rise close to 6.5V for a short duration before the
loop regulates with FB less than 4.8V. This is the same
blanking time window as for the Active Burst Mode and
can therefore be adjusted by the external CSoftS
.
In the case of VCC undervoltage, ie. VCC falls below
8.5V, the IC will be turn off with the Startup Cell
charging VCC as described earlier in this section. Once
VCC is charged above 15V, the IC will start a new
startup cycle. The same procedure applies when the
system is under Short Optocoupler fault condition, as it
will lead to VCC undervoltage.
Version 1.1
15
21 May 2004
INFINEON [ Infineon ]
