Dual-Phase, Parallelable, Average-Current-Mode

Controllers

16

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Differential Amplifier

The differential amplifier (DIFF AMP) facilitates output

voltage remote sensing at the load (Figures 3a and 3b).

It provides true differential output voltage sensing while

rejecting the common-mode voltage errors due to high-

current ground paths. Sensing the output voltage

directly at the load provides accurate load voltage

sensing in high-current environments. The VEA pro-

vides the difference between the differential amplifier

output (DIFF) and the desired output voltage. The dif-

ferential amplifier has a bandwidth of 3MHz. The differ-

ence between SENSE+ and SENSE- regulates to the

preset output voltage for the MAX5038A and regulates

to +1V for the MAX5041A.

Voltage-Error Amplifier

The VEA sets the gain of the voltage control loop and

determines the error between the differential amplifier

equals +1V.

An offset is added to the output voltage of the

VEA such that the no-load output voltage is higher than

Adaptive Voltage Positioning section and use the follow-

ing equations to calculate the no-load output voltage.

MAX5038A:

MAX5041A:

(Figure 2).

no load. To ensure that the output voltage does not

≤ +1.8V:

For MAX5041A:

The VEA output clamps to +0.9V (plus the common-

mode voltage of +0.6V), thus limiting the average maxi-

mum current from individual phases. The maximum

average-current-limit threshold for each phase is equal

to the maximum clamp voltage of the VEA divided by

the gain (18) of the current-sense amplifier. This allows

for accurate settings for the average maximum current

the amount of output voltage positioning required as

discussed in the Adaptive Voltage Positioning section

(Figures 3a and 3b).

Adaptive Voltage Positioning

Powering new-generation processors requires new

techniques to reduce cost, size, and power dissipation.

Voltage positioning reduces the total number of output

capacitors to meet a given transient response require-

ment. Setting the no-load output voltage slightly higher

than the output voltage during nominally loaded condi-

tions allows a larger downward voltage excursion when

the output current suddenly increases. Regulating at a

lower output voltage under a heavy load allows a larger

upward-voltage excursion when the output current sud-

denly decreases. A larger allowed, voltage-step excur-

sion reduces the required number of output capacitors

or allows for the use of higher ESR capacitors.

Voltage positioning and the ability to operate with multiple

reference voltages may require the output to regulate

away from a center value. Define the center value as the

voltage where the output drops (

maximum output current (Figure 5).

RV

R

V

XCC

F

REF

=−

×

[. ]

16

RV

V

R

V

X

CC

NOM

F

NOM

=−

+

×

[(

. )]

21 2

RV

V

R

V

X

CC

NOM

F

NOM

=−

+

×

[(

. )]

06

V

R

R

RR

R

V

OUT NL

IN

F

HL

L

REF











 ×

+











 ×

1

V

R

R

V

OUT NL

IN

F

OUT NOM

()

(

)

=+











 ×

1

(3)

(4)

(5)

(6)

(7)