ISL6306 Datasheet, PDF(11/33 Page) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision rDS ON or DCR Differential Current Sensing

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ISL6306 Datasheet, PDF (11/33 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision rDS ON or DCR Differential Current Sensing

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ISL6306

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 ISL6306 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

ISL6306 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 ISL6306

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 ISL6306 is active

depending on status of ENLL, the internal POR, and pending

fault states. Driving EN_VTT below 0.745V will clear all fault

states and prime the ISL6306 to soft-start when re-enabled.

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.

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.

When an OFF VID code causes shut-down, the controller

needs to be reset before it starts again.

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), when IDROOP pin is tied to FB pin. The droop scale

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

DCR or the lower MOSFET rDS(ON). COMP is tied back to FB

through an external RC 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

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+ and 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.

FN9226.1

May 5, 2008

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