ISL6334DIRZ datasheet(14/28 Pages) RENESAS

14 / 28 page

ISL6334D

FN6802 Rev 4.00

Page 14 of 28

Apr 29, 2016

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 8). 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

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 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 9 assures that the

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

in the reference voltage (output of the DAC) and offset errors in

the OFS current source, remote-sense and error amplifiers.

Intersil specifies the guaranteed tolerance of the ISL6334D to

include the combined tolerances of each of these elements.

The output of the error amplifier, VCOMP, is compared to

sawtooth waveforms to generate the PWM signals. The PWM

signals control the timing of the Intersil MOSFET drivers and

regulate the converter output to the specified reference voltage.

The internal and external circuitry, which control voltage

regulation, are illustrated in Figure 9.

The ISL6334D incorporates an internal differential remote sense

amplifier in the feedback path. The amplifier removes the

voltage error encountered when measuring the output voltage

relative to the local controller ground reference point, resulting in

a more accurate means of sensing output voltage. Connect the

microprocessor sense pins to the non-inverting input, VSEN, and

inverting input, RGND, of the remote-sense amplifier. The

remote-sense output, VDIFF, is connected to the inverting input of

the error amplifier through an external resistor.

A Digital-to-Analog Converter (DAC) generates a reference

voltage based on the state of logic signals at pins VID7 through

VID0. The DAC decodes the eight 6-bit logic signal (VID) into one

of the discrete voltages shown in Table 3 on page 15. All VID pins

have no internal pull-up current sources after tD3. After tD3, each

VID input offers a minimum 30µA pull-up to an internal 2.5V

source for use with open-drain outputs. The pull-up current

diminishes to zero above the logic threshold to protect

voltage-sensitive output devices. External pull-up resistors can

augment the pull-up current sources in case leakage into the

driving device is greater than 30µA.

ISEN

RSENSE

RISEN

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



(EQ. 7)

FIGURE 8. SENSE RESISTOR IN SERIES WITH INDUCTORS

ISEN IL

RSENSE

RISEN

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

ISEN-(n)

CURRENT

SENSE

ISEN+(n)

RISEN(n)

RSENSE

VOUT

COUT

ISL6334D INTERNAL CIRCUIT

FIGURE 9. OUTPUT VOLTAGE REGULATION LOOP

EXTERNAL CIRCUIT ISL6334D INTERNAL CIRCUIT

COMP

RFB

VDIFF

VSEN

RGND

ERROR AMPLIFIER

VOUT+

DIFFERENTIAL

REMOTE-SENSE

AMPLIFIER

VCOMP

REF

DAC

RREF

CREF

VOUT-

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