LTC 4367 Transistor burning Issues

[usama14]

Hi all.
I'm using LTC4367 for reverse polarity, OV and UV protection. I'm using the FDMD84100 Dual N channel Mosfets and the input voltage is 50V. However, when connected without any load, the output voltage is all OK at the beginning but then it gradually decreases towards zero. Also my transistors have been burnt in most cases and I've tried changing the IC and the transistors countless times. My output current requirement is 7A. OV is 58V and UV is 5V. I've used the resistors according to these values. Also, I've tested both in open load and also by attaching the load, the result is the same.

I'm attaching my schematic.

Kindly help as I'm stuck at this stage for a very long time now. Thankyou!

 

[betwixt]

I presume the source connection on Q2 is connected to +50V, it isn't shown in the schematic.
Gradual reduction in output suggests something is overheating. You are running the device at it's maximum rating, is it adequately heatsinked?

Brian.

 

[usama14]

I presume the source connection on Q2 is connected to +50V, it isn't shown in the schematic.
Gradual reduction in output suggests something is overheating. You are running the device at it's maximum rating, is it adequately heatsinked?

Brian.

Source connection is left open as this transistor is connected in a back to back common source configuration as shown below.
Also whose maximum rating are you talking about? The transistors? I am testing my setup in Airconditioned environment with fast speed fan.

 

[betwixt]

Apologies, your original schematic shows an unconnected source at pin 9 but I see from the data sheet it is an 8-pin device with internally connected source pins.

Brian.

 

[usama14]

Yes exactly. Thats why i left the source pins open.
Now coming back to the issue, any suggestions?