MP2930 - 4-PHASE PWM CONTROLLER WITH 8-BIT DAC CODE

MP2930 Rev. 1.01

www.MonolithicPower.com

11

10/30/2013

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If the RC network components are selected

such that the RC time constant (=R*C) matches

the

inductor

time

constant

(=L/DCR),

the

voltage drop across the DCR, i.e., proportional

to the channel current.

proportional to the inductor current and it can

be seen form Equation (4).

ISEN

R

DCR

L

I

SEN

I





(4)

Resistive Sensing

For accurate current sense, a current-sense

inductor can serve as the current sense

element (see Figure 3). This technique is more

accurate,

but

reduces

overall

converter

efficiency due to the additional power loss on

Equation (5) shows the ratio of the channel

ISEN

R

SENSE

R

L

I

SEN

I





(5)

CURRENT

SENSE

I

ISEN+(n)

ISEN-(n)

MP2930 INTERNAL CIRCUIT

L

n

=I

R

R

SEN

I

L

SENSE

ISEN

Figure 3

—Sense Resistor in Series with

Inductors

The inductor DCR value will increase as the

temperature increases. Therefore the sensed

current will increase as the temperature of the

current sense element increases. In order to

compensate the temperature effect on the

sensed current signal, a Positive Temperature

Coefficient (PTC) resistor can be selected for

Channel-Current Balance

is summed together and divided by the number

of active channels. The resulting average

load

current.

Channel

current

balance

is

achieved by comparing the sensed current of

each channel to the average current to make an

appropriate adjustment to the PWM duty cycle

of each channel.

Channel

current

balance

is

essential

in

achieving the thermal advantage of multiphase

operation. With good current balance, the

power loss is equally dissipated over multiple

devices and a greater area.

Voltage Regulation

The compensation network shown in Figure 4

assures that the steady-state error in the output

voltage is limited only to the error in the

reference voltage (output of the DAC) and

offset errors in the OFS current source, remote-

sense and error amplifiers.

The typical open-loop gain of error amplifier is

no less than 80dB, and the typical open-loop

bandwidth is no less than 20MHz.

R

C

R

C

MP2930 INTERNAL CIRCUIT

FB

ERROR AMPLIFIER

IDROOP

VDIFF

VSEN

RGND

DIFFERENTIAL

REMOTE-SENSE

AMPLIFIER

V

I

REF

DAC

COMP

EXTERNAL CIRCUIT

R

V

REF

REF

FB

DROOP

C

C

COMP

AVG

Figure 4

—Output Voltage and Load-line

Regulation with Offset Adjustment