Electrical – Looking for a motherboard CPU Power MOSFET replacement – is this OK to put not exact the same

mosfetmotherboard

I have a motherboard with broken PDC3094X (Potens Semiconductor) in VRM circuit. I cannot find the replacement with exact same parameters and the original part is impossible to get. I don't have a lot of experience in finding a replacement parts, so I have a big request for some help.

PDC3094X parameters are:

  • Id= 90A
  • Vds= 30V
  • Rdson= 4mOhm (@Vgs= 10V)
  • Pd= 115W
  • Qg= 24nC (@Id= 20A)
  • Ci= 2200pF
  • Co= 475pF

PDC3094X PDF datasheet: http://potens-semi.com/pdf/PDC3094X.pdf

Would that be OK to replace it with TEXAS INSTRUMENTS CSD17576Q5BT?

CSD17576Q5BT parameters are:

  • Id= 100A
  • Vds= 30V
  • Rdson= 1,7mOhm (@Vgs= 10V)
  • Pd= 125W
  • Qg= 25nC (@Id= 25A)
  • Ci= 3410pF
  • Co= 389pF

CSD17576Q5BT PDF datasheet: http://www.ti.com/lit/ds/symlink/csd17576q5b.pdf

Which other MOSFET in such package would fit? What are terms of finding a good replacement for motherboard power-line MOSFET? What parameters are the most important?

Best Answer

The first thing to ensure is that the new MOSFET will not break your circuit. Vds is the important parameter here. You want your new Vds limit to be at least as high as the old part.

Secondly, it is important that the new MOSFET does not break itself trying to work your equipment. Check that the new Id limit is at least as high as the old Id. Also check that the power dissipation of the new part is at least as high as the old one. Be careful here, sometimes they list the absolute top power dissipation if you were to provide an enormous heat sink. Make sure the power dissipation is adequate given the ambient temperature and heat sinks that will be used. Rds on is included in this section, a lower Rds means less heat generated.

Lastly, make sure that your driver will properly operate the MOSFET. This is where the Vth, Cin, and C matter. The new MOSFET Vth needs to be equal to or lower to the old Vth, this will ensure that the MOSFET is fully turned on by the provided driver voltage. The Cin and Co must be equal to or smaller. Larger capacitance will result in longer turn on and turn off times, and depending on the operating frequency of your circuit this may lead to problems.

So on the specs, this appears to the a good replacement. Now to switch it out and test. Let us know if it works!

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