VIPER012XS datasheet(23/36 Pages) STMICROELECTRONICS

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VIPer01

General description

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4.13

VCC clamp protection

This protection can occur when the IC is supplied by auxiliary winding or diode from the

output voltage, when an output overvoltage produces an increase of VCC.

If VCC reaches the clamp level VCCclamp (30 V, min. referred to GND) the current injected

into the pin is monitored and if it exceeds the internal threshold Iclamp_max (30 mA, typ.) for

more than tclamp_max (500 µs, typ.), the PWM is disabled for tRESTART (1 s, typ.) and then

activated again in soft-start phase. The protection is disabled during the soft-start time.

4.14

Disable function

When the voltage across the pin is externally pulled above VDIS_th (1.2 V typ.) for more than

tDEB (for instance by a voltage divider connected to some higher voltages), the PWM is

disabled. If the voltage divider on the DIS pin is connected to the rectified mains, as shown

in Figure 30: "Connection for input overvoltage protection (isolated or non-isolated

topologies)", an input overvoltage protection can be built.

Figure 30: Connection for input overvoltage protection (isolated or non-isolated topologies)

In case of non-isolated topologies, by following the same principle an output overvoltage

protection can be built, as shown in Figure 31: "Connection for output overvoltage

protection (non-isolated topologies)".

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