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TPS92641: Question about SW pin negative side absolute Max.

Part Number: TPS92641

Tool/software:

Hello guys,

One of my customers is evaluating TPS92641 using the device EVM for their new products.

At this moment, they have the following question.
Could you please give me your reply?

Q.
SW pin negative side absolute Max is -0.3V.
But they think SW voltage is go down less than -0.7V or more negative side until low side FET is turned on.

Is this negative pulse allowed?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • Hi Kazuya

    If an external  voltage <-0.3V applies on SW-GND, the internal ESD diode can conduct and damage.  During normal operation, the parasitic inductance on the pcb trace and bonding wire will cause transient negative spike due to the fast switching, this is normal and should have no risk.

    Thanks and best regards.

  • Hi Gui,

    Thank you very much for your reply.

    They observed that the SW terminal undershoot on TPS92461 EVM was about -3V (about 20ns pulse width) .
    After that, -1V undershoot (40ns pulse width) was continued on the EVM (total negative pulse width about 60ns).
    After that, overshoot is disappeared and SW terminal voltage is stable around 0V.

    If they observed on their own board that similar level undershoot waveform of SW terminal above, is it no problem?

    Also if the observed a lower and longer undershoot on their own board, is it problem?

    Do you have any absolute max spec of negative voltage or longest pulse width of SW terminal?

    Thank you again and best regards,
    Kazuya.

      

  • Hi Kazuya

    Did customer measure SW voltage using smallest loop as below:

    instead of:

    The second measure method involves larger voltage spike.

    Can you please share the waveform from customer?

    Thanks and best regards.

  • Hi Gui,

    Thank you very much for your supports.

    Yes, the customer measured the SW undershoot waveform with the method.

    Also we can share the waveform with you. But they don't want to disclose the waveform
    on this thread. So could you please give me your e-mail address because I'd like to discuss you offline?

    And I got new information from them.
    They replaced some original parts of the EVM with different parts they selected
    for LED current increasing.

    I got their parts list. So I'd like to share it with you too.

    Thank you again and best regards,
    Kazuya.

  • Hi Kazuya

    Yes you can send to bella-he@ti.com

    Best regards.

  • Hi Kazuya

    Did you send email?

    Best regards.

  • Hi Gui,

    Thank you very much for your telling e-mail address and I'm sorry to be late my response because I took day off.

    I sent you the waveform by e-mail.
    Could you please give me your reply?

    Your reply would would be much appreciated.

    Thank you again and best regards,
    Kazuya.  

  • Hi Kazuya

    It's ok, I saw you email. I close the thread for now , let's keep on the email page. 

    Thanks and best regards.

  • Hi Gui,

    Thank you for your supports.

    Yes, I got it.

    Thank you again and best regards,

    Kazuya.