AN4345 datasheet(18/28 Pages) STMICROELECTRONICS

18 / 28 page

Functional check

AN4345

18/28

DocID025078 Rev 1

5.3

Feedback loop failure protection

This protection is available any time IC is externally biased. As the loop is broken (R4

shorted or R5 open), VOUT1 increases and the VIPER16LD runs to its maximum current

limitation. If J1 is selected, VDD pin voltage increases as well, because it is linked to VOUT1

through diode D6.

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

down by open loop failure protection (see Figure 27 and 28), 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. The same behavior can be induced

opening the high-side resistor, R5 = R5A + R5B.

The protection acts in auto restart mode with tRESTART = 1 sec (see Figure 28). As the fault

is removed, normal operation is restored after last tRESTART interval has been completed

(see Figure 30).

Figure 25. Output short-circuit maintained:

OLP steady-state (zoom)

Figure 26. Output short-circuit removal and

converter restart

AM13831V1

tOVL

AM13832V1

tRESTART

Normal

operation

Output short is

removed here

AN4345 Datasheet(PDF) 18 Page - STMicroelectronics