We are using a LTC7000 for controlling six FBL86361 back to back.
See attached schematics:
We are able to turn on and off the outputs without any problems, but in some cases the LTC7000 gets damaged. We have so far broken about ten ICs. The Vcc out when the IC is broken, is normally close 0V. The VCC resistance to GND are in order off 1k to 0 ohm to GND. In some cases the IC package is broken like in the attachment.
We have specific cases where we know that the current limit on the input power supply, was set lower than the output constant current electronic load.
Another case was when the input pin was driven low when 80A was drive through the transistor network. The output was shut off, together with the load before the INP was put high again. After this test the VCC out was 0V and the package was burned.
Do you have any suggestions to what causing this failure mode?
And any suggested changes to the schematic to make the circuit more robust?
I notice that you have no TVS protection at the input. You also do not have any reverse kick-back protection diode at the output. I suspect that you have significant inductance in your input supply and/or at the output. You should add a TVS device, such as 5.0SMDJ36A in parallel with C5, and with very solid ground connections close the the LTC7000. Also add a reverse-biased diode such as B370-13-F in parallel with your output to protect against negative voltages. Both of these devices will soak-up energy from inductive kick when the FETs turn off.
I had the same problems and it was because of the missing shottky recovery diode at the output. It is needed in every case. Otherwise the device will be damaged because of the negative output voltage (also at TS pin) during shut off. There is only a little bit of inductance (caused by cabling) needed.