ISL6316 Datasheet, PDF(14/29 Page) Intersil Corporation – Enhanced 4-Phase PWM Controller with 6-Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current Sensing for VR10 Application

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ISL6316 Datasheet, PDF (14/29 Pages) Intersil Corporation – Enhanced 4-Phase PWM Controller with 6-Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current Sensing for VR10 Application

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ISL6316

With the internal low-offset current amplifier, the capacitor

voltage VC is replicated across the sense resistor RISEN.

Therefore the current out of ISEN+ pin, ISEN, is proportional

to the inductor current.

Equation 5 shows that the ratio of the channel current to the

sensed current ISEN is driven by the value of the sense

resistor and the DCR of the inductor.

ISEN

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

RISEN

(EQ. 5)

RESISTIVE SENSING

For accurate current sense, a dedicated current-sense

resistor RSENSE in series with each output inductor can serve

as the current sense element (see Figure 5). This technique is

more accurate, but reduces overall converter efficiency due to

the additional power loss on the current sense element

RSENSE.

Equation 6 shows the ratio of the channel current to the

sensed current ISEN.

ISEN

R-----S----E----N----S----E--

RISEN

(EQ. 6)

RSENSE VOUT

COUT

ISL6316 INTERNAL CIRCUIT

RISEN(n)

SAMPLE

HOLD

ISEN-(n)

ISEN+(n)

ISEN

-R----S-----E----N-----S----E---

RISEN

FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS

MOSFET RDS(ON) SENSING

The controller can also sense the channel load current by

sampling the voltage across the lower MOSFET RDS(ON)

(see Figure 6). The amplifier is ground-reference by

connecting the ISEN- pin to the source of the lower MOSFET.

ISEN+ pin is connected to the PHASE node through the

current sense resistor RISEN. The voltage across RISEN is

equivalent to the voltage drop across the RDS(ON) of the

lower MOSFET while it is conducting. The resulting current

out of the ISEN+ pin is proportional to the channel current IL.

ISEN

-R----D-----S----(---O-----N-----)

RISEN

SAMPLE

HOLD

ISEN+(n)

RISEN

(PTC)

ISEN-(n)

VIN

ILxRDS(ON)

N-CHANNEL

MOSFETs

ISL6316 INTERNAL CIRCUIT EXTERNAL CIRCUIT

FIGURE 6. MOSFET RDS(ON) CURRENT-SENSING CIRCUIT

Equation 7 shows the ratio of the channel current to the

sensed current ISEN.

ISEN

R-----D----S----(--O-----N----)

RISEN

(EQ. 7)

Both inductor DCR and MOSFET RDS(ON) 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 the sense resistor RISEN,

or the integrated temperature compensation function of

ISL6316 should be utilized. The integrated temperature

compensation function is described in the Temperature

Compensation section.

Channel-Current Balance

The sensed current In from each active channel are summed

together and divided by the number of active channels. The

resulting average current IAVG provides a measure of the total

load current. Channel current balance is achieved by

comparing the sampled current of each channel to the

average current to make an appropriate adjustment to the

WPM duty cycle of each channel. Intersilâs patented current-

balance method is illustrated in Figure 7. In the figure, the

average current combines with the channel 1 current I1 to

create an error signal IER. The filtered error signal modifies

the pulse width commanded by VCOMP to correct any

unbalance and force IER toward zero. The same method for

error signal correction is applied to each active channel.

FN9227.0

August 31, 2005

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