ISL6326B Datasheet, PDF(9/30 Page) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision DCR Differential Current Sensing

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ISL6326B Datasheet, PDF (9/30 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision DCR Differential Current Sensing

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ISL6326B

Functional Pin Description

VCC - Supplies the power necessary to operate the chip.

The controller starts to operate when the voltage on this pin

exceeds the rising POR threshold and shuts down when the

voltage on this pin drops below the falling POR threshold.

Connect this pin directly to a +5V supply.

GND - Bias and reference ground for the IC. The bottom

metal base of ISL6326B is the GND.

EN_PWR - This pin is a threshold-sensitive enable input for

the controller. Connecting the 12V supply to EN_PWR

through an appropriate resistor divider provides a means to

synchronize power-up of the controller and the MOSFET

driver ICs. When EN_PWR is driven above 0.875V, the

ISL6326B is active depending on status of EN_VTT, the

internal POR, and pending fault states. Driving EN_PWR

below 0.745V will clear all fault states and prime the

ISL6326B to soft-start when re-enabled.

EN_VTT - This pin is another threshold-sensitive enable

input for the controller. Itâs typically connected to VTT output

of VTT voltage regulator in the computer mother board.

When EN_VTT is driven above 0.875V, the ISL6326B is

active depending on status of EN_PWR, the internal POR,

and pending fault states. Driving EN_VTT below 0.745V will

clear all fault states and prime the ISL6326B to soft-start

when re-enabled.

FS - Use this pin to set up the desired switching frequency. A

resistor, placed from FS to ground will set the switching

frequency. The relationship between the value of the resistor

and the switching frequency will be described by an

approximate equation.

SS - Use this pin to set up the desired start-up oscillator

frequency. A resistor, placed from SS to ground will set up

the soft-start ramp rate. The relationship between the value

of the resistor and the soft-start ramp up time will be

described by an approximate equation.

VID7, VID6, VID5, VID4, VID3, VID2, VID1 and VID0 -

These are the inputs to the internal DAC that generates the

reference voltage for output regulation. Connect these pins

either to open-drain outputs with or without external pull-up

resistors or to active-pull-up outputs. All VID pins have 40ÂµA

internal pull-up current sources that diminish to zero as the

voltage rises above the logic-high level. These inputs can be

pulled up externally as high as VCC plus 0.3V.

VRSEL - use this pin to select internal VID code. When it is

connected to GND, the extended VR10 code is selected.

When itâs floated or pulled to high, VR11 code is selected.

This input can be pulled up as high as VCC plus 0.3V.

VDIFF, VSEN, and RGND - VSEN and RGND form the

precision differential remote-sense amplifier. This amplifier

converts the differential voltage of the remote output to a

single-ended voltage referenced to local ground. VDIFF is

the amplifierâs output and the input to the regulation and

protection circuitry. Connect VSEN and RGND to the sense

pins of the remote load.

FB and COMP - Inverting input and output of the error

amplifier respectively. FB can be connected to VDIFF

through a resistor. A properly chosen resistor between

VDIFF and FB can set the load line (droop), because the

sensed current will flow out of FB pin. The droop scale factor

is set by the ratio of the ISEN resistors and the inductor DCR

or the dedicated current sense resistor. COMP is tied back to

FB through an external R-C network to compensate the

regulator.

DAC and REF - The DAC pin is the output of the precision

internal DAC reference. The REF pin is the positive input of

the Error Amp. In typical applications, a 1kÎ©, 1% resistor is

used between DAC and REF to generate a precision offset

voltage. This voltage is proportional to the offset current

determined by the offset resistor from OFS to ground or

VCC. A capacitor is used between REF and ground to

smooth the voltage transition during Dynamic VIDâ¢

operations.

PWM1, PWM2, PWM3, PWM4 - Pulse width modulation

outputs. Connect these pins to the PWM input pins of the

Intersil driver IC. The number of active channels is

determined by the state of PWM3 and PWM4. Tie PWM3 to

VCC to configure for 2-phase operation. Tie PWM4 to VCC

to configure for 3-phase operation.

ISEN1+, ISEN1-; ISEN2+, ISEN2-; ISEN3+, ISEN3-;

ISEN4+, ISEN4- - The ISEN+ and ISEN- pins are current

sense inputs to individual differential amplifiers. The sensed

current is used for channel current balancing, overcurrent

protection, and droop regulation. Inactive channels should

have their respective current sense inputs left open (for

example, open ISEN4+ and ISEN4- for 3-phase operation).

For DCR sensing, connect each ISEN- pin to the node

between the RC sense elements. Tie the ISEN+ pin to the

other end of the sense capacitor through a resistor, RISEN.

The voltage across the sense capacitor is proportional to the

inductor current. Therefore, the sense current is proportional

to the inductor current, and scaled by the DCR of the

inductor and RISEN.

To match the time delay of the internal circuit, a capacitor is

needed between each ISEN+ pin and GND, as described in

the Current Sensing section.

VR_RDY - VR_RDY indicates that soft-start has completed

and the output voltage is within the regulated range around

VID setting. It is an open-drain logic output. When OCP or

OVP occurs, VR_RDY will be pulled to low. It will also be

pulled low if the output voltage is below the under-voltage

threshold.

FN9286.0

April 21, 2006

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