There's a lot of post on here about MOSFETs and ESD sensitivity. But whenever the general question is asked, people always go straight to the gate and how sensitive it is.
I've developed an LED driver board, with common-annode LEDs connected. Therefore, I have the drain of the low-side N-Channel MOSFETs exposed – and lots of them. The board has 52 of these exposed:
simulate this circuit – Schematic created using CircuitLab
Since I have so many, I really don't want to have to place 30V+ TVS diodes on every single output. If I have no choice, I guess I will. But I was just wondering – since they do have a parasitic body diode, is there any chance the drain will be okay – at least for EMC testing – by itself?
Best Answer
Yes, mosfets drains are sensitive to ESD. If you look at the Vds spec in the datasheet, it cannot be exceeded (for the IRF530, it's 100V), even for short amounts of time.
ESD over-voltage conditions can reach thousands of volts. To prevent failure of the mosfet, install ESD protection. One way to do this would be to use a TVS diode that limits the voltage on the drain to less than 100V (maybe 50V would be best).
If its a choice between placing a TVS diode or replacing the mosfet (or having an intermittent mosfet that behaves unpredictably, a TVS diode would be a better choice.
There are a few mosfets, such as the DMN61D8LQ that have ESD/diode protection built in to the part, however, there might not be one with the specs needed for your design. If needed TVS diodes could be placed on the outside of a mosfet to give it ESD protection or additional ESD protection (if the ESD rating of a mosfet isn't high enough).
Source: https://www.diodes.com/assets/Datasheets/DMN61D8LQ.pdf
If the LED's are connected to the outside world and are touchable by humans (or moving cables can generate thousands of volts on them if moving across a surface), then the mosfets need to be protected.