Datasheet

Functional check AN4165
22/37 Doc ID 023661 Rev 1
10.3 Feedback loop failure protection
When the loop is broken (R4 = R4a + R4b shorted or R3 open), the output voltage V
OUT
increases and the VIPER26 runs at its maximum current limitation. The V
DD
pin voltage
increases as well, because it is linked to the V
OUT
voltage either directly or through the
auxiliary winding.
If the V
DD
voltage reaches the V
DDclamp
threshold (23.5 V min.) in less than 50 msec, the IC
is shut down by the 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
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
t
RESTART
AM13381v1
t
OVL
t
SS
t
OVL
t
SS
AM11577v1
Output short is
removed here
t
RESTART
Normal
operation