ISL6322G Datasheet, PDF(13/39 Page) Intersil Corporation – Two-Phase Buck PWM Controller with Integrated MOSFET Drivers, I2C Interface and Phase Dropping

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ISL6322G Datasheet, PDF (13/39 Pages) Intersil Corporation – Two-Phase Buck PWM Controller with Integrated MOSFET Drivers, I2C Interface and Phase Dropping

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ISL6322G

MOSFET

DRIVER

VIN

UGATE(n)

LGATE(n)

ISL6322G INTERNAL CIRCUIT

DCR

INDUCTOR

VL(s)

VC(s)

R2*

VOUT

COUT

ISEN(n)

SAMPLE

ISEN(n)

VC(s)

RISEN

ISEN-(n)

ISEN+(n)

*R2 is OPTIONAL

FIGURE 5. INDUCTOR DCR CURRENT SENSING

CONFIGURATION

Inductor windings have a characteristic distributed

resistance or DCR (Direct Current Resistance). For

simplicity, the inductor DCR is considered as a separate

lumped quantity, as shown in Figure 5. The channel-current

IL, flowing through the inductor, passes through the DCR.

Equation 3 shows the S-domain equivalent voltage, VL,

across the inductor.

VL(s) = IL â (s â L + DCR)

(EQ. 3)

A simple R-C network across the inductor (R1 and C)

extracts the DCR voltage, as shown in Figure 5. The voltage

across the sense capacitor, VC, can be shown to be

proportional to the channel-current IL, shown in Equation 4.

--s-----â---L---

DCR

1â â

VC(s)

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

(s â R1 â C + 1)

DCR

(EQ. 4)

In some cases it may be necessary to use a resistor divider

R-C network to sense the current through the inductor. This

can be accomplished by placing a second resistor, R2,

across the sense capacitor. In these cases the voltage

across the sense capacitor, VC, becomes proportional to the

channel-current IL, and the resistor divider ratio, K.

--s-----â---L---

DCR

1ââ

VC(s)

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

(---R----1-----â---R----2----)

R1 + R2

1â

(EQ. 5)

-------R-----2--------

R2 + R1

(EQ. 6)

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 multiplied by the ratio of the resistor divider, K. If a

resistor divider is not being used, the value for K is 1.

The capacitor voltage VC, is then replicated across the

sense resistor RISEN. The current through RISEN is

proportional to the inductor current. Equation 7 shows that

the proportion between the channel-current and the sensed

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

the resistor divider ratio, and the DCR of the inductor.

ISEN

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

RISEN

(EQ. 7)

Output Voltage Setting

The ISL6322G uses a digital to analog converter (DAC) to

generate a reference voltage based on the logic signals at

the VID pins. The DAC decodes the logic signals into one of

the discrete voltages shown in Tables 2, 3, 4 and 5. In Intel

modes of operation, each VID pin is pulled up to an internal

1.2V voltage by a weak current source (40ÂµA), which

decreases to 0A as the voltage at the VID pin varies from 0

to the internal 1.2V pull-up voltage. In AMD modes of

operation the VID pins are pulled low by a weak 20ÂµA

current source. External pull-up resistors or active-high

output stages can augment the pull-up current sources, up to

a voltage of 5V.

The ISL6322G accommodates four different DAC ranges:

Intel VR10 (Extended), Intel VR11, AMD K8/K9 5-bit, and

AMD 6-bit. The state of the VRSEL and VID7 pins decide

which DAC version is active. Refer to Table 1 for a

description of how to select the desired DAC version.

TABLE 1. ISL6322G DAC SELECT TABLE

DAC VERSION

VRSEL PIN

VID7 PIN

VR10 (Extended)

VRSEL < 0.6V

VR11

0.8V < VRSEL < 3.0V

AMD 5-bit

3.0V < VRSEL < VCC

Low

AMD 6-bit

3.0V < VRSEL < VCC

High

TABLE 2. VR10 (EXTENDED) VOLTAGE IDENTIFICATION

CODES

VID4 VID3 VID2 VID1 VID0 VID5 VID6 VDAC

1 1.60000

0 1.59375

FN6715.0

May 22, 2008

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