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TPS795: How to reduce transient dip on Vin using TPS79533

Dave Lyneham
Prodigy 20 points
Part Number: TPS795

Hello,

In my established design a TPS79533 regulator is powered by a 5V supply that also powers a microcontroller.  The same microcontroller enables the TPS79533 at arbitary times during operation.  Sometimes the dip on the 5V supply upsets the microcontroller.  I can certainly add extra 100uF capacitor near the regulator on the input side and that helps greatly.

Is that the best solution here?  Would a better method be to reduce the voltage dip by slowing down the TPS79533 start up by adding a capacitor between NR/FB and ground?

Thank you very much for taking a look and your consideration of my question.

Kind regards
Dave

  • 0
    TI__Expert 4350 points
    Hi Dave,

    The startup time for the TPS795 is quite fast: 50 - 110 usec typical in the Electrical Characteristics table. Placing a capacitor on the NR pin will slow the rise of the error-amp reference input and will slow the LDO output ramp rate during startup. This will reduce the dip in the 5 V input. You can use up to 0.1 uF capacitor on the NR pin. If this does not reduce the dip sufficiently, you can add extra capacitance on the 5 V input.
  • 0 in reply to Eric.Preiss
    Prodigy 20 points
    Hello Eric,

    Thank you so much for your quick reply to my enquiry. It is good to get that confirmation. Yes those regulators do start very quickly. I will do as you suggested and fit 0.1uF between NR and GND. If dip is still unacceptable I will consider addition capacitance on the 5V input.

    Kind regards
    Dave