DAP011/DAP011C

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13

Short−Circuit or Overload Mode

There can be various events that force a fault on the

primary side controller. We can split them in different

situation, each having a particular configuration:

1. the converter regulates but the auxiliary winding

collapses: this is a typical situation linked to the

usage of a constant−current / constant−voltage

(CC−CV) type of controller. If the output current

increases, the voltage feedback loop gives up and

the current loop takes over. It means that Vout goes

low but the feedback loop is still closed because of

the output current monitoring. Therefore, seen

from the primary side, there is no fault. However,

there are numerous charger applications where the

output voltage shall not go below a certain limit,

even if the current is controlled. To cope with this

situation, the controller features a precise

undervoltage lockout comparator biased to a

VCC(min) level. When this level is crossed,

whatever the other pin conditions, pulses are

stopped and the controller enters the safe hiccup

mode, trying to restart. Figure 23 shows how the

converter will behave in this situation. If the fault

goes away, the SMPS resumes operation.

Figure 23. First Fault Mode Case, the Auxiliary Winding Collapses but Feedback is Still There