ISL6565A Datasheet, PDF(12/28 Page) Intersil Corporation – Multi-Phase PWM Controller with Precision rDS(ON) or DCR Current Sensing for VR10.X Application

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ISL6565A Datasheet, PDF (12/28 Pages) Intersil Corporation – Multi-Phase PWM Controller with Precision rDS(ON) or DCR Current Sensing for VR10.X Application

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ISL6565A, ISL6565B

ISEN

-r--D-----S----(---O-----N-----)

RISEN

VIN

CHANNEL N

UPPER MOSFET

SAMPLE

HOLD

ISEN(n)

RISEN

IL rDS(ON)

CHANNEL N

LOWER MOSFET

ISL6565A INTERNAL CIRCUIT EXTERNAL CIRCUIT

FIGURE 4. ISL6565A INTERNAL AND EXTERNAL CURRENT-

SENSING CIRCUITRY

INDUCTOR DCR SENSING (ISL6565B ONLY)

Inductor windings have a characteristic distributed

resistance or DCR (Direct Current Resistance). For

simplicity, the inductor DCR is considered as a separate

lumped quantity, as shown in Figure 5. The channel current

IL, flowing through the inductor, passes through the DCR.

Equation 5 shows the s-domain equivalent voltage, VL,

across the inductor.

VL(s) = IL â (s â L + DCR)

(EQ. 5)

A simple R-C network across the inductor (R1 and C)

extracts the DCR voltage, as shown in Figure 5. The voltage

across the sense capacitor, VC, can be shown to be

proportional to the channel current IL, shown in Equation 6.

VC(s) = (---s--ï£ï£«--â-D---s--R-----C---â--1----LR----â----C-+-----+1---ï£¸ï£¶--1----) â DCR â IL

(EQ. 6)

In some cases it may be necessary to use a resistor divider

R-C network to sense the current through the inductor. This

can be accomplished by placing a second resistor, R2,

across the sense capacitor. In these cases the voltage

across the sense capacitor, VC, becomes proportional to the

channel current IL, and the resistor divider ratio, K.

VC(s)

--------------ï£ï£«---D---s-------C---â------LR---------+-----1---ï£¸ï£¶---------------

ï£«

ï£¬

ï£

(--R-R----1-1---+-â---R-R----22---)

ï£¶

1ï£·

ï£¸

(EQ. 7)

K = R-----2--R---+--2--R-----1-

(EQ. 8)

If the R-C network components are selected such that the

RC time constant matches the inductor L/DCR time

constant, then VC is equal to the voltage drop across the

DCR multiplied by the ratio of the resistor divider, K. If a

resistor divider is not being used, the value for K is 1.

VIN

ISL6605

PWM(n)

ISL6565B INTERNAL CIRCUIT

DCR

INDUCTOR

VL(s)

VC(s)

R2*

VOUT

COUT

SAMPLE

HOLD

ISEN

VC(s) RISEN

ISEN(n)

ICOMMON

*R2 is OPTIONAL

FIGURE 5. DCR SENSING CONFIGURATION

The capacitor voltage VC, is then replicated across the

sense resistor RISEN. The regulator should have only one

RISEN resistor connected from the VOUT plane to the

ICOMMON pin. The current through RISEN is proportional to

the inductor current. Equation 9 shows that the proportion

between the channel current and the sensed current (ISEN)

is driven by the value of the sense resistor chosen, the

resistor divider ratio, and the DCR of the inductor.

---D----C-----R-----

RISEN

(EQ. 9)

Channel-Current Balance

The sampled currents, In, from each active channel are

summed together and divided by the number of active

channels. The resulting cycle average current, IAVG,

provides a measure of the total load-current demand on the

converter during each switching cycle. Channel-current

balance is achieved by comparing the sampled current of

each channel to the cycle average current, and making the

proper adjustment to each channel pulse width based on the

error. Intersilâs patented current-balance method is illustrated

in Figure 6, with error correction for channel 1 represented.

In the figure, the cycle average current combines with the

channel 1 sample, I1, to create an error signal IER.

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