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CSD18531Q5A: Question about MOSFET SOA Graph

Part Number: CSD18531Q5A
Other Parts Discussed in Thread: CSD18533Q5A,

In the datasheet for the CDS18531Q5A and many of the other TI MOSFETs, the conditions for the maximum SOA graph are stated as single pulse, Rtheta J-C = 1.0 C/W.  For what Rtheta C-A is this graph valid?

Is it the minimum (125C/W) or 1sq in of 2 oz copper (50C/W) or something else?

I am trying to select an N-ch FET for an overcurrent protection circuit that clamps the current by modulating the gate for a delay period before turning off the FET.  I am looking for a FET that can handle 4A at 20V Vd-s for at least 10mS.  Is there a way to know what will work without opening every datasheet?



  • Jim, 

    I believe the SOA testing is done on a Min Cu board, but I need to confirm. 

    However for shorter pulse durations, the heating is local therefore independent of board space. Furthermore, thermal runaway that occurs in the FETs linear region (where the SOA is of most importance) is an entirely local event that develops out of a small hot spot on the silicon, and therefore is entirely independent of board space. 

    I don't know any way of checking if the device would be fine under your conditions without checking the SOA of each part. For 10ms, looks like you are fine (with some margin) with the CSD18531Q5A. The next device down, the CSD18533Q5A it looks very borderline, so I think you have selected the right FET, unless you want to look at 40V options as well. 

    For more information about SOA and how we measure it, you can check out this blog I wrote:

    And video that is a bit more thorough: