# Need help reading mosfet Safe Operating Area graph

Im trying to figure out the current limitations of a mosfet(SISA18ADN) I'm planning to use to check how much headroom I have.

The datasheet states Continuous Drain Current that it can handle as 12.1Amps at Ta=70degreeC during 10seconds, and 38.3Amps at Tc=25C with no time specification.

But in the Safe Operating Area graph, apparently for DC it can handle less than 0.2A at 10V..? Am I getting something wrong when reading the graph or when reading the specs?

The Safe Operating Area graph is here:

• 38.3 amps must mean that the device is fully turned on, and so it doesn't have much of a voltage drop. With a 10V drop, 0.2A means: 10 times 0.2 = 5W of dissipation. 38.3A could mean very little dissipation if the voltage drop is low.
– Kaz
Feb 10, 2015 at 22:03
• @Kaz 10 times 0.2 is 5? Feb 10, 2015 at 22:05
• Ahhh! Damn, I knew I must have been making a stupid mistake. So for a 10Vds at 0.2A, Rds would have to be 50R? which means a low Vgs, etc.. Feb 10, 2015 at 22:07
• @SpehroPefhany Err, flip that left to right.
– Kaz
Feb 10, 2015 at 22:13

This 10A is the absolute limit for continuous operation: it is the highest amperage reached by the strictest dotted line (the DC line). Anything higher than 10A is outside of the DC safe area, achievable only by the time-limited safe areas. For 10 ms the device can go above 20A, but the voltage must be neither too high nor too low: it must be high enough that $R_{\text DS(on)}$ doesn't limit the current.