If you see the datasheet of any MOSFET lets say 40V, 300Amps NVBLS0D5N04M8 On semi MOSFET, on going through the datasheet you will see two values of Rds on one is typical and other is maximum, the question is which value you should choose for your design to be robust.
when you run 300Amps through the MOSFET its junction temperature will increase because of the power dissipation I^2*R, so here in this expression you see R which is Rds on, if you choose the wrong Rds on then you may get wrong power dissipation and FET could probably burn.
the Rds on mentioned here is at 25degC, when the current flows through it Junction temperature rises so therefore rds on at 25degC does not hold good, so for your design you should always choose Rds on at maximum Tj which 175 degC in this case.
so now how to find Rds on at 175degC, first step is to find normalization factor at 175 degC then multiply it with max Rds on.
so at 175 degC for this case is 1.7 then Rds on at 175degC = 1.7*0.57mohm = 0.969mohm, so now as you see the picture is clearly different now, so for your designing you should consider Rds on as 0.969mohm always.
 and how to choose it ){kind=link}
0 Comments