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TX7516EVM: Eval board not working - Short circuit ?

Bastien FAURE
Prodigy 30 points
Part Number: TX7516EVM

Hi,

I just started working on the TX7516EVM and were following the user guide.

I set the power supplies as specified on the user guide and the +5V supply showed 2Vdc & 200mA.

I’ve sprayed some freeze spray on the eval board just to see where this short circuit is coming from and 3 ICs immediately unfreezed -> U2, U3 & U13

Then I tried to power up the 2V5 & 3V3 independently using an external power supply. I have 50mA on 2V5 and >450mA on 3V3.

I suspect U13 to be the source of our problem but I might be wrong.

Thank you

  • 0
    TI__Intellectual 1670 points

    Hi,

    It is unfortunate to hear that the board is not working as expected. Since the problem seems to be related to one of the LDOs, we have quite a number of blocks in the suspect list. In order to isolate the problem, we can disconnect the supply going to different blocks and check the currents again. R167 connects the 3V3 supply going to U13 and related blocks. We can disconnect this resistor and check whether the current persists or not. You can also measure the impedance to ground at the output of the LDOs to see if there are any low impedance paths.

    Thanks and Regards

    Savyan

  • 0 in reply to Savyan Kanisserry
    Prodigy 30 points

    Hi Savyan,

    Thank you for your response, I followed your advices and here are the results :

    - R3V3_GND = 2,3 kOhms

    - R2V5_GND = 13 kOhms

    - R1V8_GND = 5,25 kOhms

    So no obvious short circuit here.

    I have then disconnected several resistors one by one with the power supply set to 200mA max :

    - With no modifications I have -> 200mA @ 4.61Vdc

    - R167 off I have -> 200mA @ 4.61Vdc

    - R230 off I have -> 200mA @ 4.61Vdc

    - R168 off I have -> 50mA @ 5Vdc & 20mA @ -5Vdc

    So with V_2P5_CPLD disconnected I don't have any more overcurrent. What should I do next ?

    Thank you,

    Bastien

  • 0 in reply to Bastien FAURE
    TI__Intellectual 1670 points

    Hi Bastien,

    In the above description, I see that the voltage at the pin is 4.61V when the current is clamped to 200mA. In the previous thread, it was mentioned that the voltage was at 2V with the current being at 200mA. Is there a difference between the two scenarios? Could you slightly increase the current limit to see if the supply is able to reach 5V? If the supply is able to reach 5V, could you check the board functionality as explained in the user guide?

    Thanks and Regards

    Savyan

  • 0 in reply to Savyan Kanisserry
    Prodigy 30 points

    Hi Savyan,

    The main difference between the 2 scenarios were that we only powered up the +5Vdc and not the -5Vdc.

    We increased the current limit and we now have +5Vdc with 450mA. The board is generating a pulse of 3V every 320µs without any button pressed. Nothing change if we press S1 or S2.

    We have been debugging this board for several hours now. Could you please send a new working board as we can not investigated further ?

    Thank you,

    Bastien

  • 0 in reply to Bastien FAURE
    TI__Intellectual 1670 points

    Hi Bastien,

    Could you drop a mail to support_us_afe_tx@list.ti.com regarding the EVM replacement?

    Thanks and Regards

    Savyan