VIPER28

Operation descriptions

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order to prevent the device overheating. The EPT pin can be connected to GND if the

function is not used.

7.13

The VIPER28 is protected against short circuit of the secondary rectifier, short circuit on the

secondary winding or a hard-saturation of fly-back transformer. Such as anomalous

condition is invoked when the drain current exceed 1s A typical.

To distinguish a real malfunction from a disturbance (e.g. induced during ESD tests) a

“warning state” is entered after the first signal trip. If in the subsequent switching cycle the

signal is not tripped, a temporary disturbance is assumed and the protection logic will be

switching cycles a real malfunction is assumed and the power MOSFET is turned OFF.

The shutdown condition is latched as long as the device is supplied. While it is disabled, no

the device enters in auto-restart mode. This behavioral, results in a low-frequency

intermittent operation (Hiccup-mode operation), with very low stress on the power circuit.

See the timing diagram of Figure 27.

Figure 27. Hiccup-mode OCP: timing diagram

Vcc

Secondary diode is shorted here

t

t

t

ON

OFF

Secondary diode is shorted here

t

t

t