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LM5106: High side driver failure

Bhaktha Keshavachar
Prodigy 60 points
Part Number: LM5106

Folks,

We have designed a control board for our motor controller using LM5106 for driving the MOSFETs on the power board. We have been using this for the past couple of months. Had one issue before which was resolved using this forum.

Now we are seeing a strange thing since morning. The driver ICs are failing rather mysteriously one after the other. We have isolated the control board for our testing. For testing we are toggling the ports at 1 KHz. The failure mode is as follows

1. The low side driver is working OK. The output port is toggling at 1 KHz

2. High side output is stuck at high as measured between pins 3 and 4, between HO and HS. We are using a isolated power supply instead of a bootstrap capacitor mostly because we have weird duty cycle requirements for driving the mosfet.

Initially there was one driver which was bad and all the others were working OK. We thought maybe it was static or some other random stuff. But after that, before replacing the failed part, we powered the  board again to retest and we had an additional failure and so on and on. We now have 5 failed out of 12. We do have a 22K resistor from the output to the respective ground. When I check the resistance of the output wrt to ground we do read 22K on all the output ports, This board was working fine before. Kind of crazy situation for us. Appreciate any pointers.

Thanks. -Bhaktha

  • 0
    TI__Mastermind 23215 points

    Hello Bhaktha,

    Thank you for the interest in the LM5106.. I have a couple of questions about the test setup for the 1kHz tests. Is the driver connected to the power MOSFETs in the this test setup? I assume in this test, there is not high voltage applied to the power train, please confirm.

    If there are not power mosfets connected, can you confirm the connection of the switch node? I am curious what the switch node is doing.

    In this test setup, do all LM5106 drivers show the HO-HS high or is it only some devices?

    Can you confirm what the voltage of the HB to HS bias supply, and the VDD voltage? Also can you comment on the power sequencing, does the LM5106 VDD start before the isolated HB-HS bias, same time, or after.

    If you can send scope plots of the driver input, HO-HS high side output, and LO output, that will help. Also on starting the circuit, can you show the VDD, HB-HS, and driver input to confirm the startup sequence.

    Regards,

  • 0 in reply to Richard Herring
    Prodigy 60 points

    Richard,

    Thanks for the prompt reply. Here are the answers ...

    The driver is not connected to the MOSFETs.

    The switch node is connected to the 0V terminal of the isolated 12v to 12v power supply. We are using this part from morn sun for the isolated power supply. IB1212XT-1WR2

    HO-HS is high only on some devices. Right now on 5 out of 12 we have on the board.

    HB-HS is 12V from the isolated DC-DC converter mentioned above. Vdd voltage is 12V from our 12V bus which we derive from another DC-DC converter. The main supply voltage for us is 70V DC.

    Power sequencing : First we turn on our processor board. At this time, there is no power to 5106 but its inputs are active, basically enable is asserted and we have 1KHz square on the IN pin. Then we turn on the power to the controller board. Not exactly sure on the sequence of Vdd and HB-HS bias voltage. I am assuming Vdd is a little ahead by the delay of the 12V-12V isolated DC-DC converter. I would assume they are powered up at the same time.

    As mentioned before, just to re-iterate LO continues to be good, we can see the square waveform.

    Let me know if we need to perform any experiments or take care of something we have missed. This was all working before very well in similar conditions. Nothing has changed from our side as far as we can tell.

    Thanks. -Bhaktha

  • 0 in reply to Bhaktha Keshavachar
    TI__Mastermind 23215 points

    Hello Bhaktha,

    It sounds like there is initially 1kHz input to the LM5106 applied, then the enable, then the VDD and HB-HS bias start with the VDD and HB bias timing not clear.

    Typically in most systems the VDD and bias is applied before control signals start. In power converters there is usually a soft start and you want the gate driver to execute the soft start PWM sequence.

    Can you try establishing VDD and HB bias before the enable of the LM5106 driver? I am not sure if the sequence you describe is causing he issue, but it sounds different form most applications.

    Regards,