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TPS61071: Overshoot/undershoot

Umberto Frangi
Expert 4045 points
Part Number: TPS61071
Other Parts Discussed in Thread: TINA-TI

Hi,

one of my customer is asking if the above waveform measured at SW pin, that is higher than 7V abs max(up to 7.7V) can break the device.

Do you have any specific suggestion to reduce it, after the customer was closely copying our EVM?

They got some failures but not sure about the cause.

Thanks

Umberto

  • 0
    TI__Mastermind 46905 points
    a voltage spike 1~2V higher than 7V at SW can't damage the device, the spike can be reduced by snubber circuit.
    what kind of failures? please measure the pin impedance to check the damaged pin.
  • 0 in reply to Jasper Li
    TI__Expert 4045 points

    Thanks,

    But do you think it is normal to break the device if you touch SW pin with a finger when device is powered?

    Umberto

  • 0 in reply to Umberto Frangi
    TI__Mastermind 46905 points

    Yes. this is possible. don't touch the device pin when it is operating, or not operating

  • 0 in reply to Jasper Li
    TI__Expert 4045 points

    Hi Jasper,

     it seems that reducing the feedback resistor value to 270K-30K the device is stable and touching it does not break any more.

    Can you explain why we wrote into datasheet:

    If for any reason the value chosen for R2 is significantly lower than 200 kΩ, additional capacitance in parallel to R1 is
    recommended, if the device shows instable regulation of the output voltage.

    Is there a way to calculate stability for the device, knowing pole/zero position?

    Or to simulate it ?

    I tried to use webench, but there is only load response, not phase/margin graph.

    And I am not sure what I can do with TINA-TI, are you familiar with the model?

    Thanks

    Umberto

  • 0 in reply to Umberto Frangi
    TI__Mastermind 46905 points
    the phase/margin graph can only be simulated with average model. but this device doesn't have average model.
    if the output effective capacitance is small, the small feedback do help to improve the stability.
    small feedback resistor reduce the impact of the touching, because the touch actually introduce some kind of impedance and cause the device abnormal operation. however, are you sure the failure customer observed is really caused by this?

    could you share the schematic and layout? and the part number of the inductor and capacitor