FAQ: Over Current Protection (OCP) in VIPer family

Document created by Online Support Moderator on Mar 24, 2017Last modified by Online Support Moderator on Mar 24, 2017
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Q:

We are building a 115khz SMPS transformer that is being used in a circuit that is using a VIPER06HS. It is in the circuit with my transformer that is outputting 5 volts at 200ma. the OCP is tripping off the VIPER unit. I would like to know more about this unit and how the OCP works? Is it on current solely or heat or what? If my transformer was oversaturating would that cause the OCP to trip.

A:

The overload protection is implemented using an integrated up-down counter. Every cycle, it is incremented or decremented depending upon the current logic detection of the limit condition or not. The limit condition is the peak drain current, IDLIM, set by the user through the RLIM resistor (in new VIPer0P and VIPerx1 families, the RLIM resistor is no more used, the IDILM is chosen through dedicated Part Numbers with different IDILM values). After the reset of the counter, if the peak drain current is continuously equal to the level IDLIM, the counter will be incremented until the fixed time, tOVL (Over Load Time), at which point the power MOSFET switching will be disabled. It will be activated again through the soft-start after the tRESTART time.
This kind of protection depends only on the drain current level. If the transformer saturates, it could cause the OCP tripping.

 

(extracted from ST Online Support)

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