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TPS25981: After overcurrent >2x ILIM / short circuit (=Fast trip) the device tries to switch on after 30µs even if we have the latch function

Andreas Kirchgraber
Intellectual 370 points
Part Number: TPS25981

Tool/software:

Problem with eFuse TPS25814LRPW

 

  • After overcurrent >2x ILIM / short circuit (=Fast trip) the device tries to switch on after 30µs even if we have the latch function

 

            

 

  • If the short circuit/overload further exists the current is limited to 1.5A and the device waits for a thermal shutdown – because oft he good connection to our PCB this point will never achieved. The output voltage is in this case in an undefinded value of about 2.5V instead of 3.3V. Attached devices shows undefined behaviour because of this wrong voltage.

 

 

 

What we need if 2 x ILim > Inow > ILIM (=Overcurrent):

 

If current limit is exceeded for a certain time, the eFuse will completely shut down and disables output voltage until a new power cycle is started (Vin off and on).

Is there an eFuse which will do that at Ilimit approx. 1.5A and Vin=3.3V?

 

 

Regards

Andreas

 

 

 

 

 

  • 0
    TI__Mastermind 38675 points

    Hi Andreas,

    Can you confirm if I am understanding you correctly. 

    Condition: You are seeing that device on your board is performing fast trip because of short circuit current and then after 30us, it restarts in current limit mode and the device is limiting the current to 1.5A and is not performing the TSD.

    Your requirement: you want the device to have regular overcurrent response of circuit breaker when it restarts in above mentioned condition.

    Am I understanding you correctly?

    How are you seeing 2.5V at output when there is an output short or the short is gone by then. If so, then how much current is expected during this current limited startup.

    Best Regards,
    Arush

  • 0
    Intellectual 370 points

    Hi Arush,

    our sink draws current (for what reason ever, probably the FPGA is defective ) at startup > 2xIlim. Then we see the fast trip condition with current limit mode.

    What we want is, that in this case the device also completely disconnect Vin from Vout, because the thermal shutdown in current limit mode will never occur on our PCBs (thermal connection is to good).

    Regards, Andreas

  • 0 in reply to Arush Gupta
    Intellectual 370 points

    TI support has become pretty bad. FAE cannot answer and you do not get an answer in the forum. I answered the questions 10 days ago.

     I'm on vacation now and can't answer any further questions in the next few weeks.

    Regards Andreas

  • 0 in reply to Andreas Kirchgraber
    TI__Mastermind 38675 points

    Hi Andreas,

    The device will perform this restart after FFT with 30us delay by design. This is present to ensure any issue like false transients don't cause system down. In your use case, it looks like the FFT is happening and afterwards the device is not performing the TSD due to less power dissipation on the device. I don't think there is any unexpected device behavior happening here.

    The only solution which I can see here use PG signal to externally stop the device. The PG signal will be low during this current limit startup. 

    This delay was my mistake. I apologies for that. 

    Best regards,
    Arush