ISL6564A Datasheet, PDF(13/28 Page) Intersil Corporation – Multiphase PWM Controller with Linear 6-Bit DAC Capable of Precision rDS(ON) or DCR Differential Current Sensing

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ISL6564A Datasheet, PDF (13/28 Pages) Intersil Corporation – Multiphase PWM Controller with Linear 6-Bit DAC Capable of Precision rDS(ON) or DCR Differential Current Sensing

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ISL6564A

PWM

ISEN

tHOLD

SAMPLE CURRENT, In

SWITCHING PERIOD

TIME

FIGURE 3. SAMPLE AND HOLD TIMING

Current Sensing

The ISL6564A supports inductor DCR sensing, MOSFET

rDS(ON) sensing, or resistive sensing techniques. The

internal circuitry, shown in Figures 4, 5, and 6, represents

channel n of an N-channel converter. This circuitry is

repeated for each channel in the converter, but may not be

active depending on the status of the PWM3 and PWM4

pins, as described in the PWM Operation section.

INDUCTOR DCR SENSING

An inductorâs winding is characteristic of a distributed

resistance as measured by the DCR (Direct Current

Resistance) parameter. Consider the inductor DCR as a

separate lumped quantity, as shown in Figure 4. The

channel current IL, flowing through the inductor, will also

pass through the DCR. Equation 4 shows the s-domain

equivalent voltage across the inductor VL.

VL = IL â (s â L + DCR)

(EQ. 4)

A simple R-C network across the inductor extracts the DCR

voltage, as shown in Figure 4.

The voltage on the capacitor VC, can be shown to be

proportional to the channel current IL, see Equation 5.

ââs

------L-------

DCR

1â â

(DCR

IL)

--------------------------------------------------------------------

(s â RC + 1)

(EQ. 5)

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.

VIN

ISL6207

PWM(n)

IL(s)

DCR

INDUCTOR

VC(s)

VOUT

COUT

ISL6564A INTERNAL CIRCUIT

RISEN(n)

(PTC)

SAMPLE

HOLD

ISEN

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

RISEN

ISEN-(n)

ISEN+(n)

FIGURE 4. DCR SENSING CONFIGURATION

The capacitor voltage VC, is then replicated across the

sense resistor RISEN. The current through the sense resistor

is proportional to the inductor current. Equation 6 shows the

proportion between the channel current and the sensed

current ISEN, is driven by the value of the sense resistor

chosen and the DCR of the inductor.

ISEN

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

RISEN

(EQ. 6)

DCR varies with temperature, so a Positive Temperature

Coefficient (PTC) resistor should be selected for the sense

resistor RISEN.

RESISTIVE SENSING

If DCR sensing is not utilized, independent current-sense

resistors in series with each output inductor can serve as the

sense element (see Figure 5). This technique is more

accurate, but reduces overall converter efficiency due to the

addition of a lossy element directly in the output path.

FN6285.1

March 20, 2007

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