Datasheet

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 V
OUT
increases and the VIPER06 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, depending on the cases.
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 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
t
RESTART
Figure 32. Output short-circuit maintained:
OLP steady-state (zoom)
Figure 33. Output short-circuit removal and
converter restart
AM13098v1
t
RESTART
t
OVL
t
SS
AM13099v1
Output short is
removed here
t
RESTART
Normal
operation