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LTC4366-2 Problem

I have designed surge protector with LTC4366.

I attached the schematic.

My problem is, when load current is 10A there is no problem. But i increased the load current to 15A LTC4366 stopped working and voltage across mosfets became near 2.5V.

Voltage between out and gate pins is -0.0024V.

What is the reason for LTC4366 i can not understand. I observed same problem with LTC4356.

Edit : LTC4366 is not damaged. Only Q2 damaged. When i change Q2 mosfet it worked.

But what is the reason for mosfet damage? Should it be C9 capacitor? Or should i attached snubber to mosfets?

Edit note.
[edited by: hguney at 9:19 PM (GMT -4) on 29 Sep 2018]
  • Hi hguney,

    The component values seem to clamp the output to 37V , what is the input voltage for your application and transient voltages?

    Since the FET is rated for high current , I am guessing the timer period that you have set 8.2pF ,with  311ms/uF it translates to 2.55msec is too large which causes the FET to fail. Was the part in OV when you increased the load from 10A to 15A. This might have caused the FET to heat up and fail before the timer timed-out. You can try reducing the timer cap. so that 4366 shuts the gate-off before it fails.

    Also , can you provide some more details , like input , output ,timer pin , Gate pin  voltage scope shots when you increase the load from say 10 to12 A so that we can give you better insights of what might be happening exactly?

    Best Regards,