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TMCS1126: Glitches on OC during power down

Ruixin Feng
Intellectual 2225 points
Part Number: TMCS1126

Tool/software:

Hi team,

With OC pull up to VS, when test OC pin during power down, there is many glitch on OC pin. In below waveform, blue is VS. purple is OC pin. you can see significant glitches during power down. After zoom in the waveform, the OC seems continuously be pull down to GND. Could you pls help to check this issue and explain the reason? Thanks! 

\

Rayna

  • 0
    TI__Expert 3600 points

    Hi Rayna,

    Do you have any waveforms showing the VOC signal as well?

    I would like to see a waveform with VOC, VS, and OC as you power down the device.

    VOC is the voltage threshold and if that voltage is also dropping as you power off the device this could potentially be the cause of the glitch you are seeing.

    Best,

    Holly

  • 0 in reply to Holly R
    TI__Intellectual 2225 points

    HI Holly,

    Blue is VOC waveform. Yellow is OC pin, Pink is VS. Is that expected behavior? The glitch happened before VOC drop, could you pls help to explain it? Thanks!

    Rayna

  • 0 in reply to Ruixin Feng
    TI__Expert 3600 points

    Rayna,

    The device is powering down and the error is occurring outside the minimum voltage operating range. It is not unreasonable to see glitches.

    Best,

    Holly

  • 0 in reply to Holly R
    TI__Intellectual 2225 points

    Hi Holly,

    did you mean the device was designed to behave like this? Not caused by VOC?  Did you test same glitch on your side?

    Rayna

  • 0 in reply to Ruixin Feng
    TI__Expert 3600 points

    Hi Rayna,

    I will test this, however, the part is not in a valid operating condition for the internal part to correctly determine whether the current is above or below VOC. If I test this on my end it will not guarantee that other devices will behave the same way.

    Please let me know the following so I can run the test on my end:

    1. Which version of the device you are using

    2. The current input during this test

    3. The slew rate of the power supply

    4. The supply voltage you are using

    Thanks,

    Holly

  • 0 in reply to Holly R
    TI__Intellectual 2225 points

    Hi Holly,

    Device is TMCS1126B1BQDVGR. The test is only related to power so there isn't input. power supply is 3.3V. Slew rate is referred to the waveform. 

    In datasheet, Vs abs is from GND-0.3V to 6V, the glitch happens in this range. So it's not reasonable to convince customer. Could you pls help to check with design about the glitch? Thanks!
    Rayna

  • 0 in reply to Ruixin Feng
    TI__Expert 3600 points

    Rayna,

    I have tested the device in lab and I see the same results you see.

    In the datasheet Vs ABS values represent the range of Vs in which no damage will be done to the device.  As stated in the datasheet this does not guarantee functional operation in that range. Functional operation is only guaranteed in the operating conditions.

     

    Regards,

    Holly