AN4106 datasheet(23/39 Pages) STMICROELECTRONICS

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AN4106

Functional check

Doc ID 023156 Rev 1

23/39

10.3

Feedback loop failure protection

As the loop is broken (R4 = R4a+R4b shorted or R3 open), the output voltage VOUT

increases and the VIPER26 runs at its maximum current limitation. The VDD pin voltage

increases as well, because it is linked to the VOUT voltage either directly or through the

auxiliary winding, depending on the cases.

If the VDD voltage reaches the VDDclamp threshold (23.5 V min.) in less than 50 msec, the IC

is shut down by open loop failure protection (see

Figure 30 and 31), otherwise by OLP, as

described in the previous section. The breaking of the loop has been simulated by shorting

the low-side resistor of the output voltage divider, R4 = R4a+R4b. The same behavior can

be induced opening the high-side resistor, R3.

Figure 26.

Output short-circuit applied: OLP

tripping

Figure 27.

Output short-circuit maintained:

OLP steady-state

Figure 28.

Output short-circuit maintained:

OLP steady-state, zoom

Figure 29.

Output short-circuit removal and

converter restart

AM11574v1

Output is shorted here

Normal

operation

AM11575v1

tRESTART

AM11576v1

tOVL

tSS

AM11577v1

Output short is

removed here

tRESTART

Normal

operation

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