ISL6366 datasheet(19/44 Pages) INTERSIL

19 / 44 page

ISL6366

FN6964.0

January 3, 2011

L/DCR OR ESL/RSEN MATCHING

Assuming the compensator design is correct, Figure 11 shows the

expected load transient response waveforms if L/DCR or

ESL/RSEN is matching the R-C time constant. When the load

current IOUT has a square change, the output voltage VOUT also

has a square response, except for the overshoot at load release.

However, there is always some PCB contact impedance of current

sensing components between the two current sensing points; it

hardly accounts into the L/DCR or ESL/RSEN matching calculation.

Fine tuning the matching is necessarily done in the board level to

improve overall transient performance and system reliability.

If the R-C timing constant is too large or too small, VC(s) will not

accurately represent real-time IOUT(s) and will worsen the

transient response. Figure 12 shows the load transient response

when the R-C timing constant is too small. VOUT will sag

excessively upon load insertion and may create a system failure

or early overcurrent trip. Figure 13 shows the transient response

when the R-C timing constant is too large. VOUT is sluggish in

drooping to its final value. There will be excessive overshoot if

load insertion occurs during this time, which may potentially hurt

the CPU reliability.

Channel-Current Balance for VR0

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 14 assures that the

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

in the reference voltage (DAC & OFFSET) and droop current

source, remote sense, and error amplifier.

The sensed average current IDROOP is tied to FB internally and

will develop voltage drop across the resistor between FB and

VOUT for droop control. This current can be disconnected from the

FB node by tying RFS_DRP high to VCC for non-droop applications.

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

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 ISL6366 does not have a unity gain amplifier in between the

feedback path and error amplifier. For remote sensing, connect the

microprocessor sensing pins to the non-inverting input, FB, via the

feedback resistor (RFB), and inverting input, RGND, of the error

amplifier. This configuration effectively removes the voltage error

encountered when measuring the output voltage relative to the local

controller ground reference point. VSEN should connect to remote

sensing’s positive rail as well for over voltage protection.

A digital-to-analog converter (DAC) generates a reference voltage,

which is programmable via SVID bus. The DAC decodes the SVID

set command into one of the discrete voltages shown in Table 4.

In addition, the output voltage can be margined in ±5mV step

between -640mV and 635mV, as shown in Table 5, via SVID set

FIGURE 11. DESIRED LOAD TRANSIENT RESPONSE

WAVEFORMS

IOUT

VOUT

FIGURE 12. LOAD TRANSIENT RESPONSE WHEN R-C TIME

CONSTANT IS TOO SMALL

IOUT

VOUT

FIGURE 13. LOAD TRANSIENT RESPONSE WHEN R-C TIME

CONSTANT IS TOO LARGE

IOUT

VOUT

FIGURE 14. OUTPUT VOLTAGE AND LOAD-LINE REGULATION

IDROOP

EXTERNAL CIRCUIT

COMP

RFB

VDROOP

ERROR

VCOMP

VOUT

RGND

AMPLIFIER

VID &

OFFSET

OVP

VSEN

ISL6366

DAC

ISL6366 Datasheet(PDF) 19 Page - Intersil Corporation

ISL6366 Datasheet(HTML) 19 Page - Intersil Corporation

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