Multiphase voltage regulator

[Bluestreak66]

Can anybody point me to some resources on multiphase voltage regulator design? Like whats used on pc motherboards and on graphics cards. I'm designing a board and trying to power several ASICs on it. I need 1.2v @around 28 amps for core voltage, specificly 2 or 3 phase. I have looked though some data sheets but have yet to see any refrence designs. Any info or chip recommendations are helpful. Thanks

[Paul Price]

I have used this chip in designing multi-phase power supplies. There is a reference design in the .pdf.

[Bluestreak66]

Yea I had looked at that chip as it it referenced in some of the FPGA documentation. However I don't believe it is Multiphase its just a Synchronous buck regulator. That does look like my best option all the 2+ multiphase regulators used a lot of passive components as well and seem to need some sort of digital control. The reason I want to do a multiphase is efficiency it extremely important in this application as well a the have the overhead to do overclocking.

[marshallh]

Check out Linear's regulator modules. Unless you really want to take the hard learning route.

[AndyC_772]

Have a look at TI, the LM25119 is a dual channel controller which can operate as two independent regulators or one regulator with 180 deg phase shift between the two halves.

[Bluestreak66]

Have a look at TI, the LM25119 is a dual channel controller which can operate as two independent regulators or one regulator with 180 deg phase shift between the two halves.

Thanks I looked it up on TI site, there is some good info on it there as well as info on multiphase converters in general. Are there any cheap easy to use controllers out there that can use 3 or more phases?

[CarlG]

You don't specify the input voltage and want device, reference design, price? High demands I say. I can't give you all that but I'd check out LTC polyphase switchers & controllers. Here's some examples:

LTC3880 dual (2phase) controller, the datasheet has an example of 1V 80A quadphase.
LTC3731 is 3-phase controller, has an example of 2.5V/100A, 6-phase.
LTC3415 integrated FETs, 7A, up to 12 phases

Quadphase is easily achived, but the current sharing might be a challenge.

[Bluestreak66]

You don't specify the input voltage and want device, reference design, price? High demands I say.

I 'm more looking for general info than specifics. I'm not sure on the input voltage myself 12- 24v maybe. I haven't seen anybody use them in custom projects before, but I know they're used in a lot of consumer gear. I'm just trying to get an idea of how feasible it would be to use in a custom project. If I do decide to use one I will probably go with a 3-phase as I believe it will give a cleaner output. Thanks for the info.

[Bluestreak66]

Lots of these controllers have the ability to synchronize with the with the clock frequency. Does that mean I can just feed the clock signal into it and the phases will be timed to reduce noise? Or does the clock need to be offset?

[AndyC_772]

The phases will more than likely be timed relative to each other and to the master clock you provide, but whether or not that reduces noise will depend on your particular design and layout.

The idea of a multi-phase controller is to improve efficiency by reducing the I2R losses in each channel, and to reduce ripple voltages on the input and output by increasing the effective switching frequency. The phase relationship between channels might result in destructive interference at some harmonics of the switching frequency (ie. good for EMI), or it might be constructive. Often there's a pin you can strap to set the phase relationship between channels, which you may want to be able to control when you go EMC testing.