MP2953B – DIGITAL PWM CONTROLLER WITH PMBUS FOR VR12.5

MP2953B Rev. 1.01

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16

10/9/2015

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FIGURE 4(a). Steady State with Load @160A

Load transient performance is illustrated in

Figures 4(b)—(d). The MP2953B adaptively

changes the switching frequency of each

individual phase during load transient to achieve

fast closed-loop speed. Only one set of loop

compensation is needed, so it is very easy to set

the loop parameter.

Fig. 4(b) shows no ring-back when the load steps

up from 36A to 180A. Fig. 4(c) shows that the

overshoot of the output voltage is small during

load release. Fig. 4(d) shows the high-load

transient rate; the output voltage is stable. The

MP2953B meets Intel VR12.5 standards with a

minimum number of output capacitors.

FIGURE 4(b). Load Step Up @ 1kHz

FIGURE 4(c). Load Step Down @ 1kHz

FIGURE 4(d). Load Step @1MHz

Power State Change

The SVID bus changes the VR into different

power states to achieve high efficiency during

light-load conditions. These states are entered by

programming the power-state register using

SVID’s SetPS command. The VR optimizes its

power loss to flatten the efficiency curve over the

operating current range with the power-state

commands issued by the CPU.

In PS0 mode, all phases run in CCM. In PS1

mode (<20A load, typically), only one phase runs

with synchronous switching; the other phases are

in tri-state. In PS2 mode (<5A load, typically),

only one phase runs in the diode emulation mode;

the switching frequency decreases automatically

due to the light-load condition.