Protection features

AN4007

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Doc ID 022455 Rev 2

2.2

Overvoltage protection

An output overvoltage protection is implemented monitoring the voltage across the auxiliary

winding during the MOSFET turn-off time, through the diode D4 and the resistor dividers R4

threshold (3 V typ.), an overvoltage event is assumed and the device is no longer allowed to

switch.

immunity and avoid that spikes erroneously trip the protection, a digital filter was

cycles before stopping operation.

The protection can be tested by opening the resistor R9. In this way the converter operates

in open loop and the excess of power with respect to the load charges the output

capacitance, increasing the output voltage as the OVP is tripped and the converter stops

switching.

In

Figure 23 and 24 it is possible to see that output voltage increases and as it reaches the

value of 6.5 V the converter stops switching. In the same figure the CONT pin voltage is

reported. The crest value of the CONT pin voltage tracks the output voltage.

Figure 23.

Overvoltage event: OVP triggering

AM11362v1

Ch2 (Max): 6.48 V

M: 400.0 µs/div