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TPS2493: It cannot turn off device when there is constant load current

liming liu
Prodigy 30 points
Part Number: TPS2493

Hello,

  I am using TPS2493 for system protection but it does not work well. The following is the schematic:

It is normally used to detect over current and then send "0V" gate voltage to turn off device Q7.  When I used resistor load for the test, the TPS2493 works fine. Once the load current is over than the limit "25A", the device Q7 is OFF and then restart the over-current detection every 2s. However, if we use current source load for the test and set the current source load is constant 26A (over than current limit), TPS2493 can not generate right gate voltage to turn off device Q7. Q7 is still on until it is blew up. It looks like Q7 worked on Non-linear region due to low gate voltage from TPS2493. I think current source load will keep current constant for some time no matter what is input voltage. During this period, although TPS2493 detects over current and tries to turn off device Q7, there is still constant current through Q7. I do not know how TPS2493 operates under this kind of test condition. I need your suggestion to deal with this issue.

Thanks,

  • 0
    TI__Guru** 105361 points

    Hi Liu,

    Please use resistive load or electronic load in CR mode or the actual load for evaluation. 

    If an electronic load is used for testing in CC mode, which turns out to be placing two current sources in series in the network. So, the output and behavior depends on the characteristics of electronic load and we may see odd behavior.

    Can you please retest with electronic load in CR mode and confirm

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 30 points

    Hi Rakesh,

      Thanks for the feedback. However, in our application, the load could be inductor load which looks like a current source. Do you have other controller to replace TPS2493 to meet our application? I know TI has LM5609 but I think we will get the same issue with this controller.

    Thanks,

    Best regards,

    Liming

  • 0 in reply to liming liu
    TI__Guru** 105361 points

    Hi Liu,

    Can you please provide filled up design calculator to first check whether the FET has required SOA for the target specifications. I have attached the excel sheet for your reference.

    As a next step, please check with our actual load. Measure Vout, GATE, timer and input current under a overload condition and share me for review.

    Thanks, Rakesh

    slvc033j.zip

  • 0 in reply to Rakesh
    Prodigy 30 points

    Hi Rakesh,

      Thanks for your feedback. It looks like the system will be back to turn on for 20ms each 2s once overcurrent is detected. I think the MOSFET temp. rise very fast during 20ms. After several times, the MOSFET blew up due to the thermal issue(Beyond SOA). I will try to reduce the Turn-on time during overcurrent to see if I can solve this issue.

    Thanks,

  • 0 in reply to liming liu
    TI__Guru** 105361 points

    Ok Liu.

    Please share update after your testing.

    Best Regards, Rakesh