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TPS25982: Negative transient limit at the out pins

Niranjan Pandian
Prodigy 50 points
Part Number: TPS25982

Tool/software:

Hello, 

I am using TPS25982 IC the below is the circuit diagram

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While testing output short circuit condition, I am seeing negative spikes of up to 9V, like the waveform below;

As per datasheet, the maximum negative spike is -0.3V on OUT pin. I have created this transient of negative spike multiple times on the IC. IC doesnt fail.

Is it because the duration of the negative spike is very small? Is there a specification in regarding the duration of the negative transient the IC can withstand? 

Even with Schottky diode, I see negative spikes upto -2V, like the waveform below. 

I am interested in knowing the maximum transient duration the IC can withstand exceeding the absolute maximum ratings?

Thank you. 

  • +1
    TI__Genius 16595 points

    Hello!

    We do not have this exact transient spec but adding higher output cap near the device and selecting the Schottky diode is key.

     

    One more thing which I suspect in your case is how are you measuring these. Best will be to measure near the device pins using tip and barrel probe. 

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    Prodigy 50 points

    Thank you Arush Gupta. 

    I will try increasing the output cap and use your recommendations for diode selection. However, it would really help, if I can get transient specs for the device.

    I did probe with tip and barrel with passive probes and also tried with active probes. 

    Can you also share failure modes of TPS25982? 

  • 0 in reply to Niranjan Pandian
    TI__Genius 16595 points
    Niranjan Pandian said:
    As per datasheet, the maximum negative spike is -0.3V on OUT pin

    It is -0.8V in datasheet. I did few test some time ago on this device but that is different from full validation. Based on that, I was seeing -1V transients as good safe limit. This is just for your reference. This is not guaranteed in datasheet and it is best to stay within the datasheet limits. 

    Is the output cap near the device pins? You can experiment with 1uF, 10uF, 20uF to see if this is helping. They should be kept near the device.

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    Prodigy 50 points

    In my circuit, efuse is withstanding repetitive spikes of up to -9V. I dont see any failure. 

    However, thank you, I will try increasing the capacitors and meet the datasheet recommended levels.