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Old 04-08-2014, 03:59 PM
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RRainbo RRainbo is offline
Join Date: Jun 2011
Location: CZ
Posts: 53

Originally Posted by Khenglish View Post

I = V / R
I = 89W / 1.371V
I = 65A total
I = 21.7A per phase

P = I^2 * R
P = 21.7A^2 * 14mOhm
P = 6.57W per phase
P = 19.7W total due to high-side power FETs alone!
Thats wrong calc. Highside mosfet is fully turn on only [(Vout/Vin)/3] of time! Conduction losses are not that important as switching losses in this case.

Originally Posted by Khenglish View Post
1. Does any other component need to be changed to accommodate the new FETs?
Maybe bootstrap capacitor will need to be bigger if you will use both highside fets or fet with higher total Q -check datasheet there should be something about selecting that cap.

Originally Posted by Khenglish View Post
2. Currently turbo turns off when the CPU is drawing high amounts of power at normal room temps with the CPU in the mid 80s. It takes several minutes of high power draw before this occurs. It will turn back on after a few seconds, then off again a few seconds later with this cycle repeating indefinitely. This does not happen in a cold environment, or if a screw up die contact so that the CPU runs hotter and can hit TJmax. My thinking is that a motherboard component is triggering an overheat signal, cutting power draw by disabling turbo to save the motherboard. The only component close to the FETs with a heat sensor are the MOSFET gate drivers. By putting in bigger FETs, will I be putting more strain on the gate driver and exacerbate this issue?
No idea how it work didnt read intel datasheet. VRM controllers have usuallly thermistors(external ntc or ptc) placed around inductors. no temp sensors in gate drivers.

Originally Posted by Khenglish View Post
3. To simplify purchasing can I buy matching high-side and low-side FETs? I was thinking of getting all mdu2654 or all mdu1512 FETs for both high side and low side.
Yes you can buy matching mosfets but best is highside fast switching and lowside low Rdson.

Originally Posted by Khenglish View Post
4. Does anyone have an mdu2654 datasheet? I'm mainly interested in the gate capacitance. I found current ratings from a screenshot, but the picture lacked the capacitance numbers. I am concerned with overloading the gate driver.
Cant help you with that sorry.

Originally Posted by Khenglish View Post
5. The FETs are far enough away from the CPU socket that I can shield the socket from my heat gun when replacing the FETs. The same cannot be said for the inductors. Downsizing the inductors and adding caps to spread out the increased ripple current can also significantly reduce voltage regulation power draw, and improve output voltage stability in the process. My thinking is that this may melt the CPU socket, but it might not since the socket was likely put on in the first place using a oven hot enough to melt lead-free solder, so maybe the socket can take the heat. Is replacing the inductors a possibility, or is melting the socket too likely?
Use proper equipment for that work not heatgun. Use alufoil as shielding and control temp and socket should survive.

What do you mean with downsizing inductors? With changing inductors you will totally change your LC filtration and also current sensing of VRM controller.
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