ISL6263A Datasheet, PDF(16/19 Page) Intersil Corporation – 5-Bit VID Single-Phase Voltage Regulator with Power Monitor for IMVP-6+ Santa Rosa GPU Core

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ISL6263A Datasheet, PDF (16/19 Pages) Intersil Corporation – 5-Bit VID Single-Phase Voltage Regulator with Power Monitor for IMVP-6+ Santa Rosa GPU Core

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ISL6263A

VDD

OCP

10ÂµA

OCSET

DROOP

VSUM

DFB

DROOP

ROCSET

VRSNS

FIGURE 9. EQUIVALENT MODEL FOR DROOP CIRCUIT USING DISCRETE RESISTOR CURRENT SENSING

The current sensing traces should be routed directly to the

inductor pads for accurate DCR voltage drop measurement.

However, due to layout imperfection, the calculated RDRP2

may still need slight adjustment to achieve optimum load line

slope. It is recommended to adjust RDRP2 after the system

has achieved thermal equilibrium at full load. For example, if

the maximum load current is 20A, one should apply a 20A

load current and look for 160mV output voltage droop. If the

voltage droop is 155mV, the new value of RDRP2 is

calculated in Equation 17:

RDRP2new

1----6---0----m-----V---

155 m V

(

(EQ. 17)

icore

ÎIcore

Vcore

ÎVcore

ÎVcore= ÎIcoreÃRdroop

FIGURE 10. DESIRED LOAD TRANSIENT RESPONSE

WAVEFORMS

For the best accuracy, the effective resistance on the DFB

and VSUM pins should be identical so that the bias current

of the droop amplifier does not cause an offset voltage.

Dynamic Droop Capacitor Design Using DCR

Sensing

Figure 10 shows the desired waveforms during load

transient response. VCCGFX needs to follow the change in

Icore as close as possible. The transient response of

VCCGFX is determined by several factors, namely the choice

of output inductor, output capacitor, compensator design,

and the design of droop capacitor CN.

If CN is designed correctly, the voltage VDROOP -VO will be

an excellent representation of the inductor current. Given the

correct CN design, VCCGFX has the best chance of tracking

ICORE, if not, its voltage will be distorted from the actual

waveform of the inductor current and worsens the transient

response. Figure 11 shows the transient response when CN

is too small allowing VCCGFX to sag excessively during the

load transient. Figure 12 shows the transient response when

CN is too large. VCCGFX takes too long to droop to its final

value.

icore

Vcore

FIGURE 11. LOAD TRANSIENT RESPONSE WHEN CN IS TOO

SMALL

icore

Vcore

FIGURE 12. LOAD TRANSIENT RESPONSE WHEN CN IS TOO

LARGE

FN9284.3

July 8, 2010

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