Why is the advantage of using VRM doublers in PC motherboards ?

[tigrou]

According this page :

VRM doublers are inserted at the place of drivers, right before a MOFSET. They distribute the power between the two lanes of MOSFETs and chokes available to each doubler, thereby, doubling the phase. This allows PWN controllers with support for up to 6 phase VRMs to be used in 12 phase VRM designs using doublers.

If I understand correctly : you need to double the number MOSFETs and chokes.
If it's the case, why not use a "true" multi-phase system (eg: why 3*2 would be cheaper than 6 if you still need to double everything).

There is probably something I am missing.

EDIT : this page also give useful info.
It looks like using doublers halves the frequency (so putting to 2 times less stress on each phase).

[amyk]

Doubling is used to get more phases than the PWM controller has. A 3*2 wouldn't make sense, because 3-phase controllers are common.

[mariush]

A lot of manufacturers these days stopped using doublers and just paralleled two power stages and their inductors and capacitors.

A 8 phase controller + doublers can be cheaper than a 14-16 phase controller and also some smaller controllers could be more flexible ... for example that 8 phase controller could be run in 6+2 or 6+1+1 modes and save another vrm controller
It may also be more advantageos for the manufacturer to stock on the 8 phase controller in huge volume and reuse it across a wide range of boards, while using a higher phase controller only on premium expensive models.

[barshatriplee]

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