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TPS259824OEVM: eFuse on EVM shuts down at 3.2 A load regardless of jumper settings

Kirk @ Santa Clara
Prodigy 90 points
Part Number: TPS259824OEVM

Hi,

     I am working with a TPS259824OEVM eval board.  It is powered by a DC power supply (12 V) and outputs to an electronic load.  I have confirmed that it has the default factory jumper configuration.

     The eFuse cuts power at 3.2 A load.  With the default jumper configuration, it should allow 5 A.  But I can move the jumper to any setting on J10 and I get the same result.

     This is an issue, because I have an eFuse implementation on a pcb that I designed that does not pass current under any circumstances.  My plan was to verify operation on the EVM and then use the same values in my design.

     Do you have any ideas about why the EVM is not performing as expected?  Thank you!

                                                                                                                                            -Kirk

 

  • 0
    TI__Guru 50445 points

    Hi Kirk,

    1. How much is current limit of input supply?

    2. What is electronic load type CC load or CR load?

    3. Are you applying load after eFuse has turned on , I mean there is 12 V at output already or there is always 3.2A load since 12V is applied at eFuse input?

    4. Can you explain test setup?

    5. How much is load cap?

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Prodigy 90 points

    Kunal,

    You were right!  My benchtop power supply was current limiting and I didn't notice.  I am now using a 40 A supply for +12 V.

    I am still not getting the results from the eFuse that I want.  The eFuse will trip if +12 V is applied to the EVM and a load of more than 300 - 400 mA is already active.  This is the test case that I believe is closest to simulating capacitor inrush current.  If I add the load *after* power is applied, rather than before, then the eFuse does not trip.

    My test setup includes a benchtop power supply provides power to the EVM, and an electronic load in constant-current mode.  There is no added capacitance.

    Adjusting dvdt, itimer or auto-retries does not seem to change the 300 - 400 mA limit that I am seeing.  I started testing with the EVM in the default configuration.

    Using Equation 1 from TI's "Managing Inrush Current" document, I believe that my system, with about 867 uF of input capacitance, will draw over 400 mA of current when power is applied, even with dvdt set to 0.5 V/ms.

    I need to find a configuration that will allow my system to power up without tripping the eFuse.  Thanks again!

                                                                                                            -Kirk

  • 0 in reply to Kirk @ Santa Clara
    TI__Guru 50445 points

    Hi Kirk,

    1. There is no cap while testing? You have removed default cap on EVM?

    2. We do not recommend testing efuse with cc load as a practical load does not behave like cc load. Also capacitor inrush current can not be simulated by cc load because cc load will try to draw current from device even when VOUT=0 but device will start providing current after the internal fet crosses its VT threshold.  Why you are not using only output cap for testing?

    3. During startup of device since device is under high thermal stress due to high power dissipation, adding an external load will add to power dissipation and device will hit thermal shutdown fast before startup. So what you are seeing is not circuit breaker of device due to current crossing current limit but it is thermal shutdown. 

    3. If you want you can use CR load during startup .

    4. I will recommend first test startup with only output cap because in a practical system during startup only cap will draw current and later other downstream load will start to draw current.

    Regards

    Kunal Goel