I have a circuit like the one shown below. To make the schematic easier to read, I only show 2 FETs in parallel. I actually have 8 identical FETs in parallel. The HT0440 is a high-side N-channel FET driver. It's controlled by a digital signal from an MCU.
Power is not switched on and off rapidly in this application, but I am still concerned about the instantaneous heating in the FETs when power is turned off. Particularly when RLoad is small and the current is high prior to being switched off. I probed the source pins of the FETs during a switch-off event and observed this curve:
It takes about 250ms for the FETs to fully turn off. RLoad in this case was 10 Ohm. I did some calculations in a spreadsheet and came up with this curve for power-vs-time in the MOSFETs during the switch-off event:
Integrating under the curve, I get about 17Ws (Watt-seconds). That's the total accumulated power loss among all 8 MOSFETs. There's a graph in the MOSFET's datasheet that shows the maximum single pulse power dissipation as a function of pulse width.
Now, I know that MOSFETs in parallel will work "nicely" with each other to share the total current because of their PTC nature. However, I don't know if it's safe to assume they will continue to work nicely together during a switch-off event. In other words, as the gate pins are being driven low, is there some property of MOSFETs that would cause one single MOSFET to end up taking the brunt of the switching power dissipation? Or will they all share the total power dissipation equally?