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TPS40210: Calculation of reset time after OC protection

Jammy Su1
Prodigy 100 points
Part Number: TPS40210

Hi Sir/Madam,

I would like to know how to calculate the rest time after OC is triggered.

According to the datasheet, can I use equation (4)~(6) to calculate?

Because the calculation value doesn't meet the measurement value.

Please give some suggestions. Thank you very much. Have a nice day.

  • 0
    TI__Guru 68495 points

    Hi Jammy,

    Thank you for considering the TPS40210.  The reset time is controlled by the SS capacitor.  Please refer to datasheet equations (4) to (6).

    Best Regards,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 100 points

    Hi Youhao,

    Thank for your quick reply.

    I choose 1uF as the SS capacitor and consider the tolerance of other parameters in equation.

     I get the reset time is about 3 seconds. Should the measurement value be equal to or greater than it?

    If the reset time is also related  to other parameters, such as the input voltage and parasitic capacitor or not? Thanks.

  • 0 in reply to Jammy Su1
    TI__Guru 68495 points

    The equations just give you a typical value, and the actual measurement can be slightly higher or lower than the calculation results. Please verify by test.  Basically the input voltage does not affect this timing during normal operation.  However, if you have a low VIN which reduces VBP, then the time can be reduced. 

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 100 points

    Hi Youhao,

    Calculated value is about 3 seconds, but measured value is about 8 seconds. Is it okay?

    Another question is about OC protection. If OC is triggered, does the gate signal try to drive MOSFET after the restart time or not?

    I measured ISNS PIN over 150mV, but IC still give a few times gate signal. Is it correct operation and why?

    Thanks. 

  • 0 in reply to Jammy Su1
    TI__Guru 68495 points

    I believe the measured 8s has the effects of the capacitor's leakage current, which reduces the effective SS current and result in longer than calculated.  In this case, you should reduce the capacitor value.  Usually larger capacitor has larger leak current.  

    Thanks,

    Youhao