AN4164 datasheet(21/38 Pages) STMICROELECTRONICS

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AN4164

Functional check

Doc ID 023660 Rev 1

21/38

6.3

Feedback loop failure protection

This protection is available any time the IC is not self-biased. As the loop is broken (RfbL

shorted or RfbH open), the output voltage VOUT increases and the VIPER06 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 34 and 35), 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, RfbL = RfbL1+RfbL2. The same behavior

can be induced opening the high-side resistor, RfbH = RfbH1+RfbH2.

Figure 30.

OLP short-circuit applied: OLP

tripping

Figure 31.

Output short-circuit maintained:

OLP steady-state

AM13096v1

Normal

operation

Output is shorted here

AM13097v1

tRESTART

Figure 32.

Output short-circuit maintained:

OLP steady-state (zoom)

Figure 33.

Output short-circuit removal and

converter restart

AM13098v1

tRESTART

tOVL

tSS

AM13099v1

Output short is

removed here

tRESTART

Normal

operation

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