MP2953B – DIGITAL PWM CONTROLLER WITH PMBUS FOR VR12.5

MP2953B Rev. 1.01

www.MonolithicPower.com

24

10/9/2015

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Over-Current Protection (OCP)

The MP2953B utilizes the valley point over-

current limit method to limit each phase current.

If the present phase current is higher than the

setting valley point, then this phase will not turn

on until its current falls below the setting level. If

the present phase is blocked for 150ns, then

the next phase will turn on instead so as to

regulate the output voltage at the set point.

The valley point over-current level can be

programmed via the PMBus to limit the per-

phase current.

The total current protection is triggered if the

sensed average total current is higher than the

OC threshold.

Since this protection averages the output

current over many switching cycles, the

average current OCP threshold can be set very

close to the expected maximum output load for

accurate over-current protection.

Fig. 14 shows the OCP process for total current

protection. The total current protection is

disabled during the soft-start process, and it is

enabled when soft start has finished.

Vout

CCM

PWM

VRRDY

OC

OCP

Iphase

Phase_OCP_LIM

Iout

500

us

Total_OCP_LIM

FIGURE 14. OC Protection for Total Current

Fig. 15 shows the process when the output is

shorted to ground. During this process, per-

phase OCP limits the phase current. After

a pre-set time, the VR is shut off by the total

current OCP.

FIGURE 15. OCP with Output Dead Short

Under-Voltage Protection (UVP)

If the output voltage is below VID – 300mV for a

given time, the system triggers UVP and

immediately shuts down by turning off all

phases.

Fig. 16 shows the UVP process.

Normally, UVP is triggered when PWM signals

are blocked by the OC signals (when the per-

phase current limit is reached) as shown in Fig.

17.

FIGURE 16. Under-Voltage Protection