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UCC28C42: Enable/Disable circuit

Vishal Kakade
Intellectual 930 points
Part Number: UCC28C42

Hello,

I am designing two power supplies using UCC28C42. I have also designed external circuits which give me input UVLO/OVLO alarm signal at 3.3V and 0V.

My UVLO alarms is a transition from 3.3V to 0V, OVLO alarms is a transition from 0V to 3.3V.

I want to use these alarm inputs to disable UCC28C42.

I am connecting UVLO alarm to CS pin through an optocoupler. and UVLO alarm to COMP pin through an optocoupler. in order to disable the controller at Lower and Upper threshold.

Please go through my design and let me know for any other alternative or reviews.

Regards

Vishal Kakade

  • 0
    TI__Mastermind 31580 points

    Hi Vishal,

    Pulling the COMP pin low will stop the PWM controller from producing gate drive pulses. Many customers use this method for turning the gate drive off in the event of an OVP. Please note that after the OVP event, the output voltage will decay and the comp pin will be released by the alarm circuit and the PWM controller will resume operation. This will result in a hiccup mode of operation.

    Whats the purpose of the UVLO alarm ? This will have to be disabled during start-up or else it will prevent the controller from starting. It should be possible to wire OR the two alarms on the secondary side and use a single opto to clamp the COMP pin on the primary side.

    Also check that with worse case opto CTR there will be enough current to pull the COMP pin low.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    Intellectual 930 points

    hello Peter,

    Pulling the COMP pin low will stop the PWM controller from producing gate drive pulses. Many customers use this method for turning the gate drive off in the event of an OVP. Please note that after the OVP event, the output voltage will decay and the comp pin will be released by the alarm circuit and the PWM controller will resume operation. This will result in a hiccup mode of operation.:

    Ans: UCC will not go to hiccup mode and my alarm pin will keep the device off as I have two supplies on my board for alarms circuits to run.

    What's the purpose of the UVLO alarm?

    Ans: Customer needs a logic 3.3V/0V alarms in case of input UVLO/OVLO and have to turn off the supply at the same time. 


    It should be possible to wire OR the two alarms on the secondary side and use a single opto to clamp the COMP pin on the primary side.

    Ans: I Can use XNOR logic for UVLO/OVLO and then give it to the optocoupler. But what's the harm in giving high signal to CS and Low to Comp separately?


    Also check that with worse case opto CTR there will be enough current to pull the COMP pin low.:

    Ans: it is taken care.

  • 0 in reply to Vishal Kakade
    TI__Mastermind 31580 points
    Hi Vishal,

    There is no harm in pulling COMP low and CS high simultaneously but it adds additional circuitry and cost.

    I will close this post as it appears that I have answered your questions.

    Regards

    Peter