MP2932 - 6-PHASE PWM CONTROLLER WITH 8-BIT ADC CODE

MP2932 Rev.1.02

www.MonolithicPower.com

16

4/30/2012

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© 2012 MPS. All Rights Reserved.

APPLICATION INFORMATION

Current Sensing Resistor

The resistors connected to the ISEN+ pins

determine the gains in the load-line regulation

loop and the channel-current balance loop as

well as setting the overcurrent trip point. Select

values for these resistors by using Equation

(15):

N

OCP

I

6

10

85

X

R

ISEN

R







(15)

the ISEN+ pin, N is the active channel number,

element, either the DCR of the inductor or

maximum

load

current

of

the

specific

application.

Load-Line Regulation Resistor

in Figure 4. Its value depends on the desired

load-line requirement of the application.

The desired load-line can be calculated by

using Equation (16):

FL

I

DROOP

V

LL

R



(16)

droop under the full load condition.

regulation resistor can be calculated by using

Equation (17):

X

R

LL

R

ISEN

NR

FB

R



(17)

the sense resistor connected to the ISEN+ pin,

depending on the sensing method.

Compensation

There are two distinct methods for achieving

the compensation.

Compensating Load-Line Regulated

Converter

The load-line regulated converter behaves in a

similar manner to a peak-current mode

controller because the two poles at the output-

filter L-C resonant frequency split with the

introduction of current information into the

control loop. The final location of these poles is

determined by the system function, the gain of

the current signal, and the value of the

Treating the system as though it were a

voltage-mode regulator by compensating the L-

C poles and the ESR zero of the voltage-mode.

R

C

C (OPTIONAL )

R

V

COMP

FB

IDROOP

VDIFF

MP2932

FB

DROOP

C

C

2

Figure 12— Compensation Circuit for

MP2932 with Load-line Regulation

chosen as outlined in “Load-Line Regulation

Resistor”. Select a target bandwidth for the

must be large enough to assure adequate

transient performance, but smaller than 1/3 of

the per-channel switching frequency. The

values

of

the

compensation

components

frequency and the ESR zero frequency.

sometimes needed to bypass noise away from

the PWM comparator (see Figure 12).