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ISO7221C output stability

Eduardo Hernandez
Prodigy 30 points
Other Parts Discussed in Thread: ISO7221C

Hello:

I am using a ISO7221C to isolate a power IGBT gate driver signal and supervisory signals. I am also using a gate driver transformer to isolate power for the gate driver and Vcc2 of the ISO7221C. Its datasheet mentions typical transient immunity of 40 kV/uS, and I am swiching 8 times slower a bus voltage of 400V. However, during switching of a high bus voltage I have been seeing that the isolated output of ISO7221C is going to zero for 3uS, and not high as is suppose to be. Does the ISO7221C has a shutdown or fault state that it sends the output for 3uS to zero?

Thank you

Eduardo Hernandez

 

  • 0
    TI__Genius 14015 points

    Hi Eduardo,

    Can you provide scope shots of what you are seeing? Also, a diagram showing your setup would be helpful.

    I don't know of any fault condition like this, but I will look into it.

    Thanks,
    Jason 

  • 0 in reply to Jason Blackman
    TI__Intellectual 970 points

    Hello Eduardo,

    Have you resolved this use-case?

    If not, it sounds like you are experiencing a CMTI event between the two ground potentials greater than the minimum 25kV/us.  This will cause the output to become corrupt and require an internal DC refresh signal to propagate (~3us) before the output is corrected.  One solution is to use a high-voltage capacitor (> isolation rating) between GND1 and GND2 for better tracking (reduced CMTI).

    Best Wishes,

    Bryce Sinclair

    IIF Applications (Lead)

  • 0 in reply to Bryce Sinclair
    Prodigy 30 points

    Hello Bryce:

    We were able to solve the issue. There was noise affecting the bias voltage of the IC. Using a separated bias transformer for bias supply going to the IC, fixed the problem.

    Regards,

    Eduardo Hernandez

    Power Supply Engineer