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SM72295: HSA and HOA pin of SM72295 have continuity when input is provided

ARUN GOPAN
Prodigy 30 points
Part Number: SM72295

Hello,

I referred SLAA602A application report to make an 850VA inverter. The gate pulses were generated using Atmega 2560 microcontroller. Obtained pulses were good and the driver SM72295 works fine. The output filter capcitor used is 275V ac rated 1uF. The issue i'm facing is that, i m able to obtain a pure sign output when voltage is measured across the open secondary(no load connected). When load is connected I'm obtaining a distorted wave. Distorted wave is obtained since one of the MOSFET is not turning on. It appear like gate and source of mosfet are short. All the components used are SMD (except some).

One another case I observed is that, in one of my board the HOA and HSA pins of my SM72295 driver IC  have continuity causing the output wave to be distorted. I have  asimilar issue in my second pcb where the issue gets cleared some time after input is turned OFF. I have used a lab power supply as input. Also I cannot probe the 12V output across the H brigde. Kindly help me to solve my problem

  • 0
    TI__Genius 12990 points
    Hi Arun,

    Welcome to e2e! thanks for asking about SM72295. Im an apps guy with this device and hope to help you.
    It seems like the two cases you explain are very similar. Is only leg-A highside driver shorted (HOA-HSA)? is the FET damaged or just the driver? Are you able to probe the gate and source pins on SM72295 during the issue? can you also probe VDD and the switch node with the same time scale if possible, this will allow us to see if the voltage on this pin is within limits. In the mean time I would like to review the portion of your schematic that includes the fets and driver, can you share this?

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

    Thanks for the reply.

    Of the two cases, the driver got damaged. There is continuity btw HSA and HOA even when the driver is removed from pcb. FET's are good.

    In the second case, the same problem exists when output of transformer is loaded. It gets alright some time after say after 5 sec, when input is removed.

    I'm able to probe every waveforms except across the sources of upper FET's. Also attaching the schematic.

    Thank you

  • 0 in reply to ARUN GOPAN
    TI__Genius 12990 points
    Hi Arun,

    Thanks for your update!

    When you say there is continuity when the driver is removed from the board, shouldnt having continuity show that the FET is bad since the terminals are normally high impedance or open? if the driver is the only thing thats damaged it may mean that the voltage rating of the device might be out of spec but if the FETs are also damaged it might be due to the switch node ringing or deadtime issues.

    I first notice that your input resistors are quite big. Its not recommended to delay the input signals by shaping them at the input rather shaping them at the output with a gate resistor. Is your deadtime from your controller?

    Maybe we should take a look at VCCA, HIA, LIA and HOA (HOA can be wrt to GND)
    This should tell us if the driver is attempting to switch properly.

    Thanks,
  • 0 in reply to Jeffrey Mueller
    TI__Genius 12990 points
    Hi Arun,

    Just wanted to make sure you were able to understand my last post?

    also can you tell me what EE is this for, solar or UPS?

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

    Sorry for the delay.

    I was able to solve all the issues. Right now  i'm getting the correct output. The probing issue was due to the input supply which i used. 

    Still I can't figure out why one of my driver IC worn out. Since its been tested with the same setup.

    Thanks for the help.

  • 0 in reply to ARUN GOPAN
    TI__Genius 12990 points
    Hi Arun,

    Thanks for the update!

    Do you mean VCC or VDD supply? what was wrong with this supply?
    So one driver is worn but the other is not? is there anything different about the two sides? can we see some waveforms to see if the signals are clean? does the part get hot? how long does it take to fail? what is the application doing at the time of failure?

    Thanks,