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UCC2626: Question about the Vref (pin 2) internal protection

John Percival
Prodigy 30 points
Part Number: UCC2626

I am using the Vref 5 Volt output (pin 2) to set a current limit reference voltage.  Can the Vref pin have a 47uF tantalum capacitor connected to ground and be safe for the IC chip when the input VDD supply is shut down?  Is there protection inside the chip to be able to discharge the capacitor rapidly during power-down?  I need an answer as soon as possible.

  • 0
    TI__Guru 65390 points

    John,

    What is the reason for the cap and why do you need to discharge it quickly during power down?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 30 points

    Adam,

    Thanks for the reply.  The capacitor (+side connected to Vref) is being used to provide a step boost to a voltage divider during initial application of power for motor starting.  As the capacitor charges, the voltage divider tapers to a steady state value.  The issue is during a short power interruption, the capacitor remains charged so the "boost" effect is not present immediately after a power interrupt ends.  A diode clamp on the negative side of the capacitor holds it to ground, while the positive side has to discharge into the Vref (pin 2) of the UCC2626.  Let me know if you want further clarification.

    Thanks,

    John.

  • 0 in reply to John Percival
    TI__Guru 65390 points

    John,

    Was this resolved?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 30 points

    Adam, Thanks.  I have not seen any technical responses regarding my question about internal protection at the Vref pin of UCC2626..  However, this issue can be considered CLOSED. The need to ground the capacitor I mentioned at the Vref (pin2) no longer exists.  A mechanical change that lightened the load on the motor being controlled has eliminated the need for the capacitor to be discharged rapidly during a power supply interrupt.

    I appreciate the E2E forum.

    Regards, John Percival, Electronic Engineer.