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

Question

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?

Answer 1

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!

Answer 2

Thank you very much for your support.

I previously made a little mistake and after you answered me I noticed that in fact the blown MOSFET was not a PDC3094X but PDC3906X:

PDC3906X datasheet: http://potens-semi.com/pdf/PDC3906X.pdf

Anyway, according to your guidelines, I searched and have found a replacement MOS from Texas Instruments. This is CSD18504Q5A:

CSD18504Q5A datasheet http://www.ti.com/lit/ds/symlink/csd18504q5a.pdf

I replaced a PDC3906X with CSD18504Q5A and the motherboard works again!

The only thing that concers me now is the root cause of the failure which seems to be the temperature of this particular 1st phase of VRM circuit. Compared to the temperature of other phases the 1st phase temperature is much higher. I think adding a radiator would be a good upgrade, therefore I wonder if it's better to put the radiator on the top or on the bottom side of the motherboard? MOSFETs drains in PPAK/SON 5x6mm packaging are soldered onto Cu pads put onto the motherboard PCB layer and I think the most heat disspation goes onto the bottom side of the motherboard.

Could you please point me the best solution for this issue?

Best regards, R.