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ISO5852S-EP: Gate control not working when desat condition is detected

Part Number: ISO5852S-EP


All indication is that the gate driver is not turning off when commanded if a desat condition is detected.  When I simulate the same condition with TI's SPICE model of the device, the gate turns off, as commanded. Scope shot below shows the main question: why is the upper gate drive not turning off?  Is it caused by desat?  What other condition could cause it?  --- scroll down to see the circuit...

here is the schematic which produced the trace above...

  • Hey Andrew,

    The DESAT threshold is ~9 V so you are close, but its perfectly possible that the DESAT isn't causing this.

    Are you able to try this as a low side driver rather than a high side driver?

    I would like to eliminate any GND transients from being the issue.

    It is possible a GND transient pushed the limits of the device and caused an over voltage condition, but through testing is needed first.



  • Daniel,

    Thanks for the reply.  I found two problems.  First, the oscilloscope I have has a nasty habit of saturating the signal if it falls off screen.  When I move the top two traces down, it reveals that the gate drive is actually ~34V (which makes sense... 20V bus voltage + 15V supply in a bootstrap configuration), and it DOES turn off when commanded.

    Second, I found the desat diode was assembled in reverse, thus boosting the desat signal and making me think there was a short.

    All is well now.