The datasheet current figures are a joke - no way you can put 186A through a small package like this - MOSFET datasheets seem routinely to use die ratings rather than package ratings for max current. The bond wires will vaporize at 186A. There's significant specs-man-ship on power MOSFET datasheets alas. The datasheet I saw has a note (a) "package limited" but it doesn't appear to be used (so we can assume all the suspect values are die-limited).
To be sensible the package dissipation on a typical PCB is upto 6W or so for 10s only (datasheet) - most people wouldn't put more than 2W through such a package for reliability. That limits the current to sqrt (2/0.0015) = 36A, but again can the bond wires or PCB traces take that continuously? Questionable unless on a 2oz IMS board perhaps.
Anyway current ratings for MOSFETs are always assuming infinite heatsink and the extreme thermal limit - you'd never want to be in that regime continuously - in practice you determine the maximum power dissipation Pd you are happy with (given package and its thermal environment), and determine the max current from I = sqrt (Pd/Ron), using worst case Ron. And if switching rapidly you'd account for switching losses too.
To be sensible the package dissipation on a typical PCB is upto 6W or so for 10s only (datasheet) - most people wouldn't put more than 2W through such a package for reliability. That limits the current to sqrt (2/0.0015) = 36A, but again can the bond wires or PCB traces take that continuously? Questionable unless on a 2oz IMS board perhaps.
Anyway current ratings for MOSFETs are always assuming infinite heatsink and the extreme thermal limit - you'd never want to be in that regime continuously - in practice you determine the maximum power dissipation Pd you are happy with (given package and its thermal environment), and determine the max current from I = sqrt (Pd/Ron), using worst case Ron. And if switching rapidly you'd account for switching losses too.
Thanks.
Kind of what I figured. For 5A you would ideally need a 3mm wide trace on 1oz copper (just simply taken from a chart not looking at length, temperature etc.
Guess I will just use the SMD controller and TO220 mosfets.
Kind of what I figured. For 5A you would ideally need a 3mm wide trace on 1oz copper (just simply taken from a chart not looking at length, temperature etc.
Guess I will just use the SMD controller and TO220 mosfets.
I think the V ratings are often at the edge as well. At .1" lead spacing I'm not real comfy with the 400+V rating many power fet's have. I'd prefer a package with .2" leads.
Probably by specifying the current under unrealistic conditions, namely 25 degrees Celsius case temperature, soldering the drain (back side of the die) straight to the exposed diepad without any bondwires at all and bonding the source with multiple unusually thick bondwires to each of the three source package pins. You need multiple thick bondwires anyway to get the specified 1.2 mohm typ., 1.5 mohm max. on resistance. If you want to spend half the budget on the package and half on the MOSFET die, that's 0.00075 ohm max. for the package including bondwires and leads.
The 150 mW maximum power dissipation you get at 10 A (or 210 mW when you use 4.5 V gate drive) should be no problem, as long as you use the MOSFET as a switch. Be careful with undervoltage conditions, when the gate-source voltage is too small to properly turn on the MOSFET, the power dissipation may get much higher.