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LMG1210EVM-012: My EVM don't work.The input power(J2) is short.

Changhong Bao
Prodigy 30 points
Part Number: LMG1210EVM-012
Other Parts Discussed in Thread: LMG1210

My EVM don't work. When the input power(J2) is powered on, the power is short. As I tested, the pins of the Q1(GaN) are shot with each other. Can you help me solve my problem. Thanks.

  • 0
    TI__Genius 12990 points

    Hi Changhong,

    Thanks for reaching out on LMG1210 EVM and sorry to hear about the issue your having. Let me try to help with this debug to see whats happening on the EVM.

    I understand that when you try to apply voltage to J2 the supply is shorted. Attempting to debug, you realized that the drain and source pins of the high-side GaN (Q1) are short. This might happen if the high-side GaN was damaged. There are a few things to test in order to find out what is damaged and how it got damaged:

    0) at what test conditions did you see this issue happen?

    1) is the high-side drain to source only shorted or is the gate to source shorted as well?

    2) is the low-side GaN (Q2) drain to source also short?

    3) is the LMG1210 is producing an output on HO and LO? are you in PWM mode or IIM mode? If using PWM mode, what dead-time are you using?

    4) what bus voltage and switching frequency are you using?

    5) is anything burned on the board? If not, does removing Q1 from the board allow you to put a voltage on J2 without a short?

    if we can answer these questions we should be able to move on to the next steps of debugging, let me know if you have any additional questions.

    thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 30 points

    Hi, Jeffrey:

         Thank you for replying. My answers is as below:

    0) at what test conditions did you see this issue happen?

    BCH:Test load is empty. I removed L2, and connected the output to an oscilloscope at  DC 50Ohm test condition. The input voltage is 64V. The bias voltage is 7V.

    1) is the high-side drain to source only shorted or is the gate to source shorted as well?

    BCH: The high-side drain to source and the gate to sorce are all shorted.

    2) is the low-side GaN (Q2) drain to source also short?

    BCH: No, the low-side GaN drain is not short.

    3) is the LMG1210 is producing an output on HO and LO? are you in PWM mode or IIM mode? If using PWM mode, what dead-time are you using?

    BCH: Yes ,the LMG1210 was producing an output on HO and LO in PWM mode. I did vary the dead-time, but I didn't notice the value, and I had varied it again. I guess it reached a limitation.

    4) what bus voltage and switching frequency are you using?

    BCH: The bus voltage is 3V, and switching frequency is 66MHz.

    5) is anything burned on the board? If not, does removing Q1 from the board allow you to put a voltage on J2 without a short?

    BCH: Nothing else is burned. The short disapears after I removed Q1.

  • 0 in reply to Changhong Bao
    TI__Genius 12990 points
    Hi Changhong,

    thanks for your update,
    The input voltage is 64V which should not be a problem however the switching frequency is 66MHz which should not be possible with EPC2001. The rise and fall times seen with this larger gate charge FET prevents switching the EVM above 15 MHz. In order to switch above 15 MHz you need to use EPC2016, which has a similar compatible footprint. In order to switch at 50MHz and above there needs to be a synchronous bootstrap to allow the LMG1210 internal bootstrap circuit to charge the bootstrap as fast as possible. This needs to be realized not using the EVM. If the EVM is used to switch a fast switch frequency its possible to not have enough time to allow the bootstrap cap time to charge, making the HB-HS supply drive the high-side gate in the linear region which could heat up the FET and damage it. To confirm a low HB-HS voltage, probe the HB pin w.r.t HS pin and make sure this is at 4.5-5V through out the switching period. Can you share a waveform of HO-HS and HB-HS voltage with a new high-side FET? (use the pig-tail probe method and same V/div of a few cycles)

    thanks,
  • 0 in reply to Jeffrey Mueller
    Prodigy 30 points

    Hi, Jeffrey:

         Thank you for replying. This does help us. We will change the GaN(Q1) to a good one. And my work about this is done here. My other workmates may contract you or your workmates at other time. Thanks for your help again. See you.

         Good luck!