ISL6334DIRZ datasheet(13/28 Pages) INTERSIL

13 / 28 page

FN6802.2

August 31, 2010

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.

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

RC time constant (= R*C) matches the inductor time

constant (= L/DCR), the voltage across the capacitor VC is

equal to the voltage drop across the DCR, i.e., proportional

to the channel current.

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.

Because of the internal filter at ISEN- pin, one capacitor, CT,

is needed to match the time delay between the ISEN- and

ISEN+ signals. Select the proper CT to keep the time

constant of RISEN and CT (RISEN x CT) close to 27ns.

Equation 6 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.

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.

The same capacitor CT is needed to match the time delay

between ISEN- and ISEN+ signals. Select the proper CT to

keep the time constant of RISEN and CT (RISEN x CT) close to

27ns.

Equation 7 shows the ratio of the channel current to the

sensed current ISEN.

The inductor DCR 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 ISL6334D should be

utilized. The integrated temperature compensation function is

described in “External Temperature Compensation” on

page 22.

Channel-Current Balance

The sensed current In from each active channel is 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 sensed current of each channel to the

average current to make an appropriate adjustment to the

PWM duty cycle of each channel with Intersil’s patented

current-balance method.

Channel current balance is essential in achieving the

thermal advantage of multiphase operation. With good

current balance, the power loss is equally dissipated over

multiple devices and a greater area.

Voltage Regulation

The compensation network shown in Figure 6 assures that

the steady-state error in the output voltage is limited only to

FIGURE 4. DCR SENSING CONFIGURATION

ISEN IL

DCR

RISEN

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

ISEN-(n)

CURRENT

SENSE

VIN

ISEN+(n)

PWM(n)

ISL6596

RISEN(n)

DCR

INDUCTOR

VOUT

COUT

VC(s)

IL s

()

ISL6334D INTERNAL CIRCUIT

VC s

()

DCR

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

⋅

⎝⎠

⎛⎞

DCR IL

⋅

()

⋅

sRC 1

⋅

()

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

(EQ. 5)

ISEN

DCR

RISEN

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

⋅

(EQ. 6)

ISEN

RSENSE

RISEN

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

⋅

(EQ. 7)

FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS

ISEN IL

RSENSE

RISEN

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

ISEN-(n)

CURRENT

SENSE

ISEN+(n)

RISEN(n)

RSENSE

VOUT

COUT

ISL6334D INTERNAL CIRCUIT

ISL6334D

ISL6334DIRZ Datasheet(PDF) 13 Page - Intersil Corporation

ISL6334DIRZ Datasheet(HTML) 13 Page - Intersil Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL