Datasheets isl6307a Datasheet

Download

Page 1

ISL6307A

Data Sheet February 6, 2006

Ultra-high bandwidth 6-Phase PWM Controller with 8 Bit VID Code Capable of Precision R

DS(ON)

or DCR Differential

Current Sensing

The ISL6307A controls microprocessor core voltage regulation by driving up to 6 synchronous-rectified buck channels in parallel. Multiphase buck converter architecture uses interleaved timing to multiply channel ripple frequency and reduce input and output ripple currents. Lower ripple results in fewer components, lower component cost, reduced power dissipation, and smaller implementation area.

Microprocessor loads can generate load transients with extremely fast edge rates. The ISL6307A features a high bandwidth control loop and ripple frequencies up to 12MHz to provide optimal response to the transients.

The ISL6307A senses current by utilizing patented techniques to measure the voltage across the on resistance, R inductor during the lower MOSFET conduction intervals. Current sensing provides the needed signals for precision droop, channel-current balancing, and overcurrent protection. A programmable internal temperature compensation function is implemented to effectively compensate for the temperature coefficient of the current sense element.

A unity gain, differential amplifier is provided for remote voltage sensing. Any potential difference between remote and local grounds can be completely eliminated using the remote-sense amplifier. Eliminating ground differences improves regulation and protection accuracy. The thresholdsensitive enable input is available to accurately coordinate the start up of the ISL6307A with any other voltage rail. Dynamic-VID™ technology allows seamless on-the-fly VID changes. The offset pin allows accurate voltage offset settings that are independent of VID setting.

, of the lower MOSFETs or DCR, of the output

DS(ON)

FN9236.0

Features

• Precision Multiphase Core Voltage Regulation

- Differential Remote Voltage Sensing

- ±0.5% System Accuracy Over Life, Load, Line and

Temperature

- Adjustable Precision Reference-Voltage Offset

• Precision R

DS(ON)

- Accurate Load-Line Programming

- Accurate Channel-Current Balancing

- Differential Current Sense

• Microprocessor Voltage Identification Input

- Dynamic VID™ Technology

- 8-Bit VID Icode with 6.25mV step

- 0.5V to 1.600V operation range

• Threshold-Sensitive Enable Function for Power Sequencing and VTT Enable

• Driver enable output for application with DrMOS device

• Thermal Monitoring

• Programmable Temperature Compensation

• Overcurrent Protection

• Overvoltage Protection with OVP Output Indication

• 2, 3, 4, 5 or 6 Phase Operation

• Adjustable Switching Frequency up to 2MHz per Phase

• QFN Package Option

- QFN Compliant to JEDEC PUB95 MO-220 QFN - Quad

Flat No Leads - Product Outline

- QFN Near Chip Scale Package Footprint; Improves

PCB Efficiency, Thinner in Profile

• Pb-Free Plus Anneal Available (RoHS Compliant)

or DCR Current Sensing

Ordering Information

PART

NUMBER

(Note)

ISL6307ACRZ ISL6307ACRZ 0 to 70 48 Ld 7x7 QFN L48.7x7

ISL6307AIRZ ISL6307AIRZ -40 to 85 48 Ld 7x7 QFN L48.7x7

*Add “-T” suffix to part number for tape and reel packaging.

NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.

PAR T

MARKING

TEMP.

(°C)

PACKAGE

(Pb-Free)

PKG.

DWG. #

CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.

1-888-INTERSIL or 1-888-468-3774

| Intersil (and design) is a registered trademark of Intersil Americas Inc.

All other trademarks mentioned are the property of their respective owners.

Page 2

ISL6307A

Pinout

VID7

VID6

VID5

VID4

VID3

VID2

VID1

VID0

DRVEN

OFS

IOUT

DAC

ISL6307A (48 LD QFN)

TOP VIEW

VR_HOT

48 47 46 45 44 43 42 41 40 39 38 37

VR_FAN

VR_RDY

GND

EN_VTT

EN_PWR

ISEN6-

ISEN6+

PWM6

PWM3

ISEN3+

ISEN3-

ISEN1-

ISEN1+

PWM1

PWM4

ISEN4+

ISEN4-

ISEN2-

ISEN2+

PWM2

13 14 15 16 17 18 19 20 21 22 23 24

COMP

VDIFF OVP

IDROOP

RGND

VSEN

VCC

TCOMP

ISEN5-

ISEN5+

REF

PWM5

FN9236.0

February 6, 2006

Page 3

ISL6307A Block Diagram

VDIFF

VR_RDY

OVP

ISL6307A

VCC

RGND

VSEN

DRVEN

OFS

REF

DAC

VID7

VID6

OVP

+200mV

OFFSET

SOFT-START

AND

FAULT LOGIC

OVP

DRIVE

POWER-ON

CLOCK AND SAWTOOTH

GENERATOR

∑

RESET (POR)

THREE-STATE

PWM

∑

PWM

0.875V

EN_VTT

0.875V

EN_PWR

PWM1

PWM2

PWM3

PWM4

VID5

VID4

VID3

VID2

VID1

VID0

COMP

IOUT

IDROOP

DYNAMIC

VID

D/A

∑

CHANNEL CURRENT BALANCE

E/A

OC2

OC1

I_TOT

I_TRIP

MONITORING

1 N

THERMAL

PWM

CHANNEL

DETECT

TEMPERATURE

COMPENSATION

TEMPERATURE

COMPENSATION

GAIN

CHANNEL

CURRENT

SENSE

PWM5

PWM6

ISEN1+

ISEN1-

ISEN2+

ISEN2-

ISEN3+

ISEN3-

ISEN4+

ISEN4-

ISEN5+

ISEN5-

ISEN6+

ISEN6-

GND

VR_FAN

VR_HOT

TCOMP

FN9236.0

February 6, 2006

Page 4

ISL6307A

Typical Application - 6-Phase Buck Converter with R

+5V

VCC

NTC2

+5V

PWM

GND

PWM

GND

PWM

GND

PWM

GND

PWM

GND

ISL6609

DRIVER

VCC

ISL6609

DRIVER

VCC

ISL6609

DRIVER

VCC

ISL6609

DRIVER

VCC

ISL6609

DRIVER

VTT

VR_RDY

VID7

VID6

VID5

VID4 VID3 VID2

VID1 VID0

OVP

VR_FAN

VR_HOT

+5V

IOUT

IDROOP

VDIFF

VSEN

RGND

EN_VTT

ISL6307A

IOUT

TCOMP

OFS

EXTERNAL TCOMP COMPENSATION

NETWORK

COMP

REF

DAC

VCC

GND

DRVEN

PWM6

ISEN6-

ISEN6+

PWM4

ISEN4-

ISEN4+

PWM2

ISEN2-

ISEN2+

PWM1

ISEN1-

ISEN1+

PWM3

ISEN3-

ISEN3+

PWM5

ISEN5-

ISEN5+

EN_PWR

OFS

+12V

+5V

DS(ON)

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

Sensing and External TCOMP

VIN

µP

LOAD

VIN

NTC

+5V

PWM

GND

VCC

ISL6609

DRIVER

BOOT

UGATE

PHASE

LGATE

VIN

FN9236.0

February 6, 2006

Page 5

ISL6307A

Typical Application - 6-Phase Buck Converter with R

+5V

VCC

EN ISL6609

DRIVER

VCC

GND

PWM

ISL6609

DRIVER

VCC

ISL6609

DRIVER

VCC

EN ISL6609

DRIVER

GND

VCC

GND

ISL6609

DRIVER

VTT

VR_RDY

VID7

VID6

VID5

VID4 VID3 VID2

VID1 VID0

OVP

VR_FAN

VR_HOT

+5V

IOUT

IDROOP

VDIFF

VSEN

RGND

EN_VTT

ISL6307A

IOUT

TCOMP

+5V

OFS

COMP

EN_PWR

REF

DAC

VCC

GND

DRVEN

PWM6

ISEN6-

ISEN6+

PWM4

ISEN4-

ISEN4+

PWM2

ISEN2-

ISEN2+

PWM1

ISEN1-

ISEN1+

PWM3

ISEN3-

ISEN3+

PWM5

ISEN5-

ISEN5+

+12V

PWM

GND

+5V

PWM

+5V

PWM

+5V

DS(ON)

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

Sensing and Integrated TCOMP

VIN

µP

LOAD

VIN

NTC

+5V

PWM

GND

VCC

ISL6609

DRIVER

BOOT

UGATE

PHASE

LGATE

VIN

FN9236.0

February 6, 2006

Page 6

ISL6307A

Typical Application - 6-Phase Buck Converter with DCR Sensing and External TCOMP

VTT

VR_RDY

VID7

VID6

VID5

VID4

VID3

VID2

VID1 VID0

OVP

VR_FAN

VR_HOT

+5V

IOUT

IDROOP

VDIFF

VSEN

RGND

EN_VTT

ISL6307A

IOUT

TCOMP

OFS

NTC2

EXTERNAL TCOMP

COMPENSATION

NETWORK

COMP

REF

DAC

VCC

GND

DRVEN

PWM6

ISEN6-

ISEN6+

PWM4

ISEN4-

ISEN4+

PWM2

ISEN2-

ISEN2+

PWM1

ISEN1-

ISEN1+

PWM3

ISEN3-

ISEN3+

PWM5

ISEN5-

ISEN5+

EN_PWR

OFS

+12V

+5V

PWM

GND

PWM

GND

PWM

GND

PWM

GND

PWM

GND

VCC

ISL6609

DRIVER

ISL6609

DRIVER

ISL6609

DRIVER

ISL6609

DRIVER

ISL6609

DRIVER

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

VIN

µP

LOAD

VIN

NTC

+5V

PWM

GND

VCC

ISL6609

DRIVER

BOOT

UGATE

PHASE

LGATE

VIN

FN9236.0

February 6, 2006

Page 7

ISL6307A

Typical Application - 6-Phase Buck Converter with DCR Sensing and Integrated TCOMP

VTT

VR_RDY

VID7

VID6

VID5

VID4 VID3 VID2

VID1 VID0

OVP

IOUT

VR_FAN

VR_HOT

+5V

IDROOP

VDIFF

VSEN

RGND

EN_VTT

IOUT

TCOMP

+5V

COMP

ISL6307A

OFS

REF

DAC

VCC

GND

DRVEN

PWM6

ISEN6-

ISEN6+

PWM4

ISEN4-

ISEN4+

PWM2

ISEN2-

ISEN2+

PWM1

ISEN1-

ISEN1+

PWM3

ISEN3-

ISEN3+

PWM5 ISEN5-

ISEN5+

EN_PWR

FSOFS

+12V

+5V

PWM

GND

PWM

GND

PWM

GND

PWM

GND

PWM

GND

VCC

ISL6609

DRIVER

ISL6609

DRIVER

ISL6609

DRIVER

ISL6609

DRIVER

ISL6609

DRIVER

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

BOOT

UGATE

PHASE

LGATE

VIN

µP

LOAD

VIN

NTC

+5V

VCC

EN ISL6609

PWM

GND

DRIVER

BOOT

UGATE

PHASE

LGATE

VIN

FN9236.0

February 6, 2006

Page 8

ISL6307A

Absolute Maximum Ratings

Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+6V

All Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . GND -0.3V to V

ESD (Human Body Model). . . . . . . . . . . . . . . . . . . . . . . . . . . . . >2kV

ESD (Machine Model) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .>200V

ESD (Charged Device Model) . . . . . . . . . . . . . . . . . . . . . . . . >1.5kV

+ 0.3V

Thermal Information

Thermal Resistance (Typical, Notes 1, 2) θJA (°C/W) θJC (°C/W)

QFN Package. . . . . . . . . . . . . . . . . . . . 32 6.5

Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . 150°C

Maximum Storage Temperature Range. . . . . . . . . . . -65°C to 150°C

Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . . 300°C

Operating Conditions

Supply Voltage, VCC (5V bias mode, Note 3) . . . . . . . . . . +5V ±5%

Ambient Temperature (ISL6307ACRZ) . . . . . . . . . . . . . 0°C to 70°C

Ambient Temperature (ISL6307AIRZ) . . . . . . . . . . . . .-40°C to 85°C

CAUTION: Stress above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied.

NOTES:

is measured in free air with the component mounted on a high effective thermal conductivity test board with “direct attach” features. See

1. θ

Tech Brief TB379

2. For θ

, the “case temp” location is the center of the exposed metal pad on the package underside.

Electrical Specifications Operating Conditions: VCC = 5V or ICC < 25mA. Unless Otherwise Specified

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

VCC SUPPLY CURRENT

Nominal Supply VCC = 5VDC; EN_PWR = 5VDC; R

ISEN1 = ISEN2 = ISEN3 = ISEN4 = -70µA

Shutdown Supply VCC = 5VDC; EN_PWR = 0VDC; R

POWER-ON RESET AND ENABLE

POR Threshold VCC Rising 4.3 4.5 4.70 V

VCC Falling 3.7 3.9 4.20 V

EN_PWR Threshold Rising 0.850 0.875 0.910 V

Hysteresis - 130 - mV

Falling 0.720 0.745 0.775 V

EN_VTT Threshold Rising 0.850 0.875 0.910 V

Hysteresis - 130 - mV

Falling 0.720 0.745 0.775 V

REFERENCE VOLTAGE AND DAC

System Accuracy of ISL6307ACRZ (VID = 1V-1.6V), T

System Accuracy of ISL6307ACRZ (VID = 0.5V-1V), T

System Accuracy of ISL6307AIRZ (VID = 1V-1.6V), T

System Accuracy of ISL6307AIRZ (VID = 0.5V-1V), T

VID Pull Up -60 -40 -20 µA

VID Input Low Level --0.4V

VID Input High Level 0.8 - - V

DAC Source Current -47mA DAC Sink Current - - 300 µA REF Source Current 45 50 55 µA REF Sink Current 45 50 55 µA

= 0°C to 70°C

= -40°C to 85°C

(Note 3) -0.5 - 0.5 %VID

(Note 3) -0.9 - 0.9 %VID

(Note 3) -0.6 - 0.6 %VID

(Note 3) -1 - 1 %VID

= 100kΩ,

= 100kΩ -1012mA

-1518mA

FN9236.0

February 6, 2006

Page 9

ISL6307A

Electrical Specifications Operating Conditions: VCC = 5V or ICC < 25mA. Unless Otherwise Specified (Continued)

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

PIN-ADJUSTABLE OFFSET

Voltage at OFS Pin for ISL6307ACRZ Offset resistor connected to ground 392 400 408 mV

Voltage below VCC, offset resistor connected to VCC 1.568 1.600 1.632 V

Voltage at OFS Pin for ISL6307AIRZ Offset resistor connected to ground 388 400 412 mV

Voltage below VCC, offset resistor connected to VCC 1.552 1.600 1.648 V

OSCILLATORS

Accuracy of Switching Frequency Setting R

Adjustment Range of Switching Frequency (Note 4) 0.08 - 2.0 MHz

Soft-start Ramp Rate (Note 5, 6) R Adjustment Range of Soft-start Ramp Rate (Note 4) 0.625 - 6.25 mV/µs

PWM GENERATOR

Sawtooth Amplitude -1.5- V

Max Duty Cycle - 66.7 - %

ERROR AMPLIFIER

Open-Loop Gain R

Open-Loop Bandwidth C

Slew Rate C

Maximum Output Voltage 3.8 4.3 4.9 V

Output High Voltage @ 2mA 3.6 - - V

Output Low Voltage @ 2mA --1.2V

REMOTE-SENSE AMPLIFIER

Bandwidth (Note 4) - 20 - MHz Output High Current VSEN - RGND = 2.5V -500 - 500 µA Output High Current VSEN - RGND = 0.6 -500 - 500 µA

PWM OUTPUT

PWM Output Voltage LOW Threshold Iload = ±500µA--0.5V PWM Output Voltage HIGH Threshold Iload = ±500µA4.3--V

DRIVER ENABLE OUTPUT

DRVEN Output Voltage LOW With 1.250kΩ resistor pull up to 5V, I DRVEN Output Voltage HIGH With 1.250kΩ resistor pull up to 5V, I

SENSE CURRENT OUTPUT (IDROOP and IOUT)

Sensed Current Tolerance ISEN1 = ISEN2 = ISEN3 = ISEN4 = ISEN5 = ISEN6 = 80µA 768084 µA Overcurrent Trip Level 90 100 110 µA

Maximum Voltage at IDROOP and IOUT pins

THERMAL MONITORING

TM Input Voltage for VR_FAN Trip 1.6 1.65 1.69 V

TM Input Voltage for VR_FAN Reset 1.89 1.93 1.98 V

TM Input Voltage for VR_HOT Trip 1.35 1.4 1.44 V

TM Input Voltage for VR_HOT Reset 1.6 1.65 1.69 V Leakage current of VR_HOT With external pull-up resistor connected to 5V - - 30 µA VR_HOT Low Voltage With 1.250kΩ resistor pull up to 5V, I Leakage Current of VR_FAN With external pull-up resistor connected to 5V - - 30 µA VR_FAN Low Voltage With 1.250kΩ resistor pull up to 5V, I

= 100kΩ 225 250 275 kHz

= 100kΩ - 1.563 - mV/µs

= 10kΩ to ground (Note 4) - 96 - dB

= 100pF, RL = 10kΩ to ground (Note 4) - 100 - MHz

= 100pF (Note 4) - 20 - V/µs

= 4mA - - 0.9 V

VR_HOT

= 4mA 3.8 - - V

VR_HOT

-2- V

= 4mA - - 0.3 V

VR_HOT

= 4mA - - 0.3 V

VR_FAN

FN9236.0

February 6, 2006

Page 10

ISL6307A

Electrical Specifications Operating Conditions: VCC = 5V or ICC < 25mA. Unless Otherwise Specified (Continued)

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

VR READY AND PROTECTION MONITORS

Leakage Current of VR_RDY With external pull-up resistor connected to 5V - - 30 µA

VR_RDY Low Voltage I

Under Voltage Trip of VR-RDY VSEN Falling 48 50 52 %VID

VR-RDY Reset Voltage VSEN Rising 58 60 62 %VID

Overvoltage Protection Threshold Before valid VID 1.250 1.275 1.300 V

After valid VID, the voltage above VID 150 175 200 mV

Overvoltage Reset Threshold 0.38 0.40 0.42 V

OVP Output High Voltage I

OVP Output Low Voltage I

NOTES:

3. These parts are designed and adjusted for accuracy with all errors in the voltage loop included.

4. Spec guaranteed by design.

5. During soft-start, VDAC rises from 0 to 1.1V first and then ramp to VID voltage after receiving valid VID input.

6. Soft-start ramp rate is determined by the adjustable soft-start oscillator frequency at the speed of 6.25mV per cycle.

= 4mA - - 0.3 V

VR_RDY

= 4mA 4.5 - - V

OVP

= 4mA - - 0.25 V

OVP

FN9236.0

February 6, 2006

Page 11

ISL6307A

Functional Pin Description

VCC - Supplies all 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 ISL6307A 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 ISL6307A 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 ISL6307A to soft-start when re-enabled.

EN_VTT - This pin is another threshold-sensitive enable input for the controller. It’s typically connected to VTT output of VTT voltage regulator in the computer mother board. When EN_VTT is driven above 0.875V, the ISL6307A 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 ISL6307A to soft-start when reenabled.

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 40.

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 14.

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

These are the inputs to the internal DAC that provide 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. VID7-VID0 have 40µA internal pull-up current sources that diminish to zero as the voltage rises above the logic-high level. These inputs can be pulled up as high as VCC plus 0.3V.

When a VID code causes a shut-off, the controller needs to be reset before it will start again.

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. Connect VSEN and RGND to the sense pins of the remote load.

VDIFF - VDIFF is the amplifier’s output and the input to the regulation and protection circuitry. It should be connected to FB through a resistor.

FB and COMP - Inverting input and output of the error amplifier respectively. FB is connected to VDIFF through a resistor. A negative current, proportional to output current is present on the FB pin. A properly sized resistor between VDIFF and FB sets the load-line (droop). The droop scale factor is set by the ratio of the ISEN resistors and the lower MOSFET R

. COMP is tied back to FB through an

DS(ON)

external R-C network to compensate the regulator.

DAC and REF - The DAC output pin is the output of the precision internal DAC reference. The REF input pin is the positive input of the Error Amp. In typical applications, a 1kΩ, 1% resistor is used between DAC and REF to generate a precise 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 VID™ operations.

PWM1, PWM2, PWM3, PWM4, PWM5, PWM6 - Pulsewidth 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, PWM4, PWM5 and PWM 6. Tie PWM3 to VCC to configure for 2-phase operation. Tie PWM4 to VCC to configure for 3-phase operation. Tie PWM5 to VCC to configure for 4-phase operation. Tie PWM6 to VCC to configure for 5-phase operation.

ISEN1+, ISEN1-; ISEN2+, ISEN2-; ISEN3+, ISEN3-; ISEN4+, ISEN4-; ISEN5+, ISEN5-; ISEN6+, ISEN6- - The

ISEN+ and ISEN- pins are current sense inputs to individual differential amplifiers. The sensed current is used as a reference for channel balancing, protection, and regulation. Inactive channels should have their respective current sense inputs left open (for example, for 3-phase operation open ISEN4+).

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, R

ISEN

. The voltage across the sense capacitor is proportional to the inductor current. The sense current is proportional to the output current, and scaled by the DCR of the inductor and R

ISEN

When configured for R

current sensing, the ISEN1-,

DS(ON)

ISEN2-, ISEN3-, ISEN4-, ISEN5-, ISEN6- pins are grounded at the lower MOSFET sources. The ISEN1+, ISEN2+, ISEN3+, ISEN4+, ISEN5+, ISEN6+ pins are then held at a virtual ground, such that a resistor connected between them, and the drain terminal of the associated lower MOSFET, will carry a current proportional to the current flowing through that channel. The current is determined by the negative

FN9236.0

February 6, 2006

Page 12

ISL6307A

voltage developed across the lower MOSFET’s R which is the channel current scaled by R

DS(ON)

and R

DS(ON)

ISEN

VR_RDY - VR_RDY is used as an indication of the end of soft-start with certain delay per Intel VR11. It is an opendrain logic output that is low impedance until the soft-start is completed. It will be pulled low again once the undervoltage point is reached.

OFS - The OFS input pin provides means to program a DC offset current for generating a DC offset voltage at the REF input. The offset current is generated via an external resistor and precision internal voltage references. The polarity of the offset is selected by connecting the resistor to GND or VCC. For no offset, the OFS pin should be left unterminated.

TCOMP - Temperature compensation scaling input. The voltage sensed on the TM pin is utilized as the temperature input to adjust ldroop and the over current protection limit to effectively compensate for the temperature coefficient of the current sense element. To implement the integrated temperature compensation, a resistor divider circuit is needed as shown in the typical application diagrams. Changing the ratio of the resistor values will set the gain of the integrated thermal compensation. When integrated temperature compensation function is not used, connect TCOMP to GND.

OVP - The Overvoltage protection output indication pin. This pin can be pulled to VCC and is latched when an overvoltage condition is detected. When not used, keep this pin open.

IDROOP - The output pin of sensed average channel current which is proportional to load current. In the application which does not require load-line, leave this pin open. In the application which requires load-line, connect this pin to FB so that the sensed average current will flow through the resistor between FB and VDIFF to create a voltage drop which is proportional to load current.

IOUT - IOUT has the same output as IDROOP with additional OCP adjustment function. In actual application, a resistor needs to be placed between IOUT and GND to ensure the proper operation. The voltage at IOUT pin will be proportional to the load current. If the voltage is higher than 2V, ISL6307A will go into OCP mode. The OCP trip level can be adjusted by changing the resistor value.

DRVEN - Driver enable output pin. This pin can be used to enable the MOSFET drivers which have enable pins such as ISL6609, ISL6608 or other DrMOS devices. If ISL6307A is used with Intersil’s ISL6612 drivers, it’s not necessary to use this pin.

TM - TM is an input pin for VR temperature measurement. Connect this pin through a NTC thermistor to GND and a resistor to 5V. The voltage at this pin is proportional to the VR temperature. ISL6307A monitors the VR temperature based on the voltage at TM and triggers VR_FAN and VR_HOT signals based on the temperature thresholds.

VR_HOT - An indication output pin of high VR temperature.

It is an open-drain logic output with low impedance. It will be pulled high when measured VR temperature reaches certain level.

VR_FAN - An indication output pin of VR temperature high warning with open-drain logic. It will be pulled high when measured VR temperature reaches certain level. VR_FAN will be pulled high before VR_HOT.

Operation

Multiphase Power Conversion

Microprocessor load current profiles have changed to the point that the advantages of multiphase power conversion are impossible to ignore. The technical challenges associated with producing a single-phase converter which is both cost-effective and thermally viable, have forced a change to the cost-saving approach of multiphase. The ISL6307A controller helps reduce the complexity of implementation by integrating vital functions and requiring minimal output components. The block diagrams on pages 4, 5, 6 and 7 provide top level views of multiphase power conversion using the ISL6307A controller.

IL1 + IL2 + IL3, 7A/DIV

IL3, 7A/DIV

PWM3, 5V/DIV

IL2, 7A/DIV

PWM2, 5V/DIV

IL1, 7A/DIV

PWM1, 5V/DIV

1µs/DIV

FIGURE 1. PWM AND INDUCTOR-CURRENT WAVEFORMS

Interleaving

The switching of each channel in a multiphase converter is timed to be symmetrically out of phase with each of the other channels. In a 3-phase converter, each channel switches 1/3 cycle after the previous channel and 1/3 cycle before the following channel. As a result, the three-phase converter has a combined ripple frequency three times greater than the ripple frequency of any one phase. In addition, the peak-topeak amplitude of the combined inductor current is reduced in proportion to the number of phases (Equations 1 and 2). Increased ripple frequency and lower ripple amplitude mean that the designer can use less per-channel inductance and lower total output capacitance for any performance specification.

FOR 3-PHASE CONVERTER

FN9236.0

February 6, 2006

Page 13

ISL6307A

Figure 1 illustrates the multiplicative effect on output ripple frequency. The three channel currents (IL1, IL2, and IL3) combine to form the AC ripple current and the DC load current. The ripple component has three times the ripple frequency of each individual channel current. Each PWM pulse is terminated 1/3 of a cycle after the PWM pulse of the previous phase. The peak-to-peak current for each phase is about 7A, and the DC components of the inductor currents combine to feed the load.

To understand the reduction of ripple current amplitude in the multiphase circuit, examine the equation representing an individual channel’s peak-to-peak inductor current.

VINV

–()V

OUT

------------------------------------------------------=

LfSV

In Equation 1, V

and V

OUT

are the input and output

OUT

(EQ. 1)

voltages respectively, L is the single-channel inductor value, and f

is the switching frequency.

INPUT-CAPACITOR CURRENT, 10A/DIV

CHANNEL 3 INPUT CURRENT 10A/DIV

CHANNEL 2 INPUT CURRENT 10A/DIV

CHANNEL 1 INPUT CURRENT 10A/DIV

1µs/DIV

FIGURE 2. CHANNEL INPUT CURRENTS AND INPUT-

CAPACITOR RMS CURRENT FOR 3-PHASE CONVERTER

The output capacitors conduct the ripple component of the inductor current. In the case of multiphase converters, the capacitor current is the sum of the ripple currents from each of the individual channels. Compare Equation 1 to the expression for the peak-to-peak current after the summation of N symmetrically phase-shifted inductor currents in Equation 2. Peak-to-peak ripple current decreases by an amount proportional to the number of channels. Outputvoltage ripple is a function of capacitance, capacitor equivalent series resistance (ESR), and inductor ripple current. Reducing the inductor ripple current allows the designer to use fewer or less costly output capacitors.

VINNV

–()V

OUT

(EQ. 2)

------------------------------------------------------------=

CPP,

LfSV

Another benefit of interleaving is to reduce input ripple current. Input capacitance is determined in part by the maximum input ripple current. Multiphase topologies can

improve overall system cost and size by lowering input ripple current and allowing the designer to reduce the cost of input capacitance. The example in Figure 2 illustrates input currents from a three-phase converter combining to reduce the total input ripple current.

The converter depicted in Figure 2 delivers 36A to a 1.5V load from a 12V input. The RMS input capacitor current is 5.9A. Compare this to a single-phase converter also stepping down 12V to 1.5V at 36A. The single-phase converter has 11.9A RMS input capacitor current. The single-phase converter must use an input capacitor bank with twice the RMS current capacity as the equivalent three-phase converter.

Figures 25, 26 and 27 in the section entitled Input Capacitor Selection can be used to determine the input-capacitor RMS current based on load current, duty cycle, and the number of channels. They are provided as aids in determining the optimal input capacitor solution. Figure 28 shows the single phase input-capacitor RMS current for comparison.

PWM Operation

The timing of each converter leg is set by the number of active channels. The default channel setting for the ISL6307A is four. One switching cycle is defined as the time between PWM1 pulse termination signals. The pulse termination signal is an internally generated clock signal which triggers the falling edge of PWM1. The cycle time of the pulse termination signal is the inverse of the switching frequency set by the resistor between the FS pin and ground. Each cycle begins when the clock signal commands the channel-1 PWM output to go low. The PWM1 transition signals the channel-1 MOSFET driver to turn off the channel1 upper MOSFET and turn on the channel-1 synchronous MOSFET. In the default channel configuration, the PWM2 pulse terminates 1/4 of a cycle after PWM1. The PWM3 output follows another 1/4 of a cycle after PWM2. PWM4 terminates another 1/4 of a cycle after PWM3.

If PWM3 is connected to VCC, two channel operation is selected and the PWM2 pulse terminates 1/2 of a cycle later. Connecting PWM4 to VCC selects three channel operation and the pulse-termination times are spaced in 1/3 cycle increments. Connecting both PWM3 and PWM4 to VCC selects single-channel operation.

Once a PWM signal transitions low, it is held low for a minimum of 1/3 cycle. This forced off time is required to ensure an accurate current sample. Current sensing is described in the next section. After the forced off time expires, the PWM output is enabled. The PWM output state is driven by the position of the error amplifier output signal, V

, minus the current correction signal relative to the

COMP

sawtooth ramp as illustrated in Figure 7. When the modified V transitions high. The MOSFET driver detects the change in state of the PWM signal and turns off the synchronous (lower) MOSFET and turns on the upper MOSFET. The

voltage crosses the sawtooth ramp, the PWM output

COMP

FN9236.0

February 6, 2006

Page 14

ISL6307A

PWM signal will remain high until the pulse termination signal marks the beginning of the next cycle by triggering the PWM signal low.

Current Sampling

During the forced off-time following a PWM transition low, the associated channel current sense amplifier uses the ISEN inputs to reproduce a signal proportional to the inductor current, I period after each PWM goes low and continuously gets sampled for 1/3 period, or until the PWM goes high, whichever comes first. No matter the current sense method, the sense current, I inductor current. Coincident with the falling edge of the PWM signal, the sample and hold circuitry samples the sensed current signal I

Therefore, the sample current, I output current and held for one switching cycle. The sample current is used for current balance, load-line regulation, and overcurrent protection.

. This current gets sampled starting 1/6

, is simply a scaled version of the

SEN

, as illustrated in Figure 3.

SEN

, is proportional to the

PWM

pass through the DCR. Equation 3 shows the s-domain equivalent voltage across the inductor V

VLILsL DCR+⋅()⋅=

(EQ. 3)

A simple R-C network across the inductor extracts the DCR voltage, as shown in Figure 4.

The voltage on the capacitor V proportional to the channel current I



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

⋅ 1+



DCR

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

DCR I

sRC 1+⋅()

, can be shown to be

, see Equation 4.

⋅()⋅

(EQ. 4)

If the R-C network components are selected such that the RC time constant (= R*C) matches the inductor time constant (= L/DCR), the voltage across the capacitor V

equal to the voltage drop across the DCR, i.e. proportional to the channel current.

ISL6609

ILs()

DCR

INDUCTOR

VC(s)

OUT

SEN

0.5Tsw

SAMPLE CURRENT, I

SWITCHING PERIOD

TIME

FIGURE 3. SAMPLE AND HOLD TIMING

Current Sensing

The ISL6307A supports inductor DCR sensing, MOSFET R

sensing, or resistive sensing techniques. The

DS(ON)

internal circuitry, shown in Figures 4, 5, and 6, represents one channel of an N-channel converter. This circuitry is repeated for each channel in the converter, but may not be active depending on the status of the PWM3 and PWM4 pins, as described in the PWM Operation section.

INDUCTOR DCR Sensing

An inductor’s winding is characteristic of a distributed resistance as measured by the DCR (Direct Current Resistance) parameter. Consider the inductor DCR as a separate lumped quantity, as shown in Figure 4. The channel current I

, flowing through the inductor, will also

PWM(n)

ISL6307A INTERNAL CIRCUIT

SAMPLE

HOLD

SEN

FIGURE 4. DCR SENSING CONFIGURATION

DCR

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

ISEN

ISEN-(n)

ISEN+(n)

ISEN(n)

(PTC)

With the internal low-offset current amplifier, the capacitor voltage V Therefore the current out of ISEN+ pin, I

is replicated across the sense resistor R

, is proportional

SEN

ISEN

to the inductor current.

Equation 5 shows that the ratio of the channel current to the sensed current I

is driven by the value of the sense

SEN

resistor and the DCR of the inductor.

DCR

SENIL

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

⋅=

ISEN

(EQ. 5)

FN9236.0

February 6, 2006

Page 15

ISL6307A

Resistive Sensing

For accurate current sense, a dedicated current-sense resistor R serve as the current sense element (see Figure 5). This technique is more accurate, but reduces overall converter efficiency due to the additional power loss on the current sense element R

Equation 6 shows the ratio of the channel current to the sensed current I

SENIL

ISL6307A INTERNAL CIRCUIT

FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS

MOSFET R

The controller can also sense the channel load current by sampling the voltage across the lower MOSFET R (see Figure 6). The amplifier is ground-reference by connecting the ISEN- pin to the source of the lower MOSFET. ISEN+ pin is connected to the PHASE node through the current sense resistor R across R R resulting current out of the ISEN+ pin is proportional to the channel current I

ISEN

of the lower MOSFET while it is conducting. The

DS(ON)

in series with each output inductor can

SENSE

SEN

SENSE

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

⋅=

ISEN

SENSE

. The voltage

ISEN

ISEN(n)

OUT

SAMPLE

HOLD

SEN

DS(ON)

SENSE

--------------------------=

ISEN

Sensing

ISEN-(n)

ISEN+(n)

is equivalent to the voltage drop across the

(EQ. 6)

OUT

DS(ON)

SEN

SAMPLE

HOLD

ISL6307A INTERNAL CIRCUIT EXTERNAL CIRCUIT

FIGURE 6. MOSFET R

DS ON()

----------------------------=

ISEN

DS(ON)

ISEN+(n)

ISEN

(PTC)

ISEN-(n)

CURRENT-SENSING CIRCUIT

DS ON()

N-CHANNEL MOSFETs

Equation 7 shows the ratio of the channel current to the sensed current I

SEN

-------------------------=

DS ON()

Both inductor DCR and MOSFET R

ISEN

SEN

(EQ. 7)

value will

DS(ON)

increase as the temperature increases. Therefore the sensed current will increase as the temperature of the current sense element increases. In order to compensate the temperature effect on the sensed current signal, a Positive Temperature Coefficient (PTC) resistor can be selected for the sense resistor R

, or the integrated

ISEN

temperature compensation function of ISL6307A should be utilized. The integrated temperature compensation function is described in the Temperature Compensation section.

Channel-Current Balance

The sensed current In from each active channel are summed together and divided by the number of active channels. The resulting average current I

provides a measure of the

AVG

total load current. Channel current balance is achieved by comparing the sampled current of each channel to the average current to make an appropriate adjustment to the PWM duty cycle of each channel. Intersil’s patented currentbalance method is illustrated in Figure 7. The average current combines with the channel 1 current I error signal I width commanded by V force I

. The filtered error signal modifies the pulse

to correct any unbalance and

COMP

toward zero. The same method for error signal

to create an

correction is applied to each active channel.

FN9236.0

February 6, 2006

Page 16

ISL6307A

FILTER

SAWTOOTH SIGNAL

f(jω)

AVG

÷ N

PWM1

COMP

FIGURE 7. CHANNEL-1 PWM FUNCTION AND CURRENT-

BALANCE ADJUSTMENT

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 integrating compensation network shown in Figure 8 assures that the steady-state error in the output voltage is limited only to the error in the reference voltage (output of the DAC) and offset errors in the OFS current source, remote-sense and error amplifiers. Intersil specifies the guaranteed tolerance of the ISL6307A to include the combined tolerances of each of these elements.

The output of the error amplifier, V sawtooth waveform 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 internal and external circuitry which control

voltage regulation is illustrated in Figure 8.

, is compared to the

COMP

EXTERNAL CIRCUIT ISL6307A INTERNAL CIRCUIT

REF

DROOP

OUT

REF

COMP

DAC

REF

IDROOP

VDIFF

VSEN

RGND

AVG

ERROR AMPLIFIER

DIFFERENTIAL REMOTE-SENSE AMPLIFIER

COMP

FIGURE 8. OUTPUT VOLTAGE AND LOAD-LINE

REGULATION WITH OFFSET ADJUSTMENT

The ISL6307A incorporates an internal differential remotesense amplifier in the feedback path. The amplifier removes the voltage error encountered when measuring the output voltage relative to the local controller ground reference point, resulting in a more accurate means of sensing output voltage. Connect the microprocessor sense pins to the noninverting input, VSEN, and inverting input, RGND, of the remote-sense amplifier. The remote-sense output, V

DIFF

, is connected to the inverting input of the error amplifier, FB, through an external resistor, R

A digital to analog converter (DAC) generates a reference voltage based on the state of logic signals at pins VID7 through VID0. The DAC decodes the 8-bit logic signal (VID) into one of the discrete voltages shown in Table 1. Each VID input offers a 45µA pull-up to an internal 2.5V source for use with open-drain outputs. The pull-up current diminishes to zero above the logic threshold to protect voltage-sensitive output devices. External pull-up resistors can augment the pull-up current sources if case leakage into the driving device is greater than 45µA.

Load-Line Regulation

Some microprocessor manufacturers require a preciselycontrolled output resistance. This dependence of output voltage on load current is often termed “droop” or “load-line” regulation. By adding a well controlled output impedance, the output voltage can effectively be level shifted in a direction which works to achieve the load-line regulation required by these manufacturers.

FN9236.0

February 6, 2006

Page 17

ISL6307A

TABLE 1. VID CODE

VID7

800mV

VID6

400mV

VID5

200mV

100mV

VID3

50mV

VID2

25mV

VID1

12.5mV

VID0

6.25mV

DAC

VO LTAGE

VID4

00000000OFF

00000001OFF

000000101.60000

000000111.59375

000001001.58750

000001011.58125

000001101.57500

000001111.56875

000010001.56250

000010011.55625

000010101.55000

000010111.54375

000011001.53750

000011011.53125

000011101.52500

000011111.51875

000100001.51250

000100011.50625

000100101.50000

000100111.49375

000101001.48750

000101011.48125

000101101.47500

000101111.46875

000110001.46250

000110011.45625

000110101.45000

000110111.44375

000111001.43750

000111011.43125

000111101.42500

000111111.41875

001000001.41250

001000011.40625

001000101.40000

001000111.39375

001001001.38750

001001011.38125

001001101.37500

TABLE 1. VID CODE (Continued)

VID4

VID7

800mV

VID6

400mV

VID5

200mV

100mV

VID3

50mV

VID2

25mV

VID1

12.5mV

VID0

6.25mV

VO LTAGE

001001111.36875

001010001.36250

001010011.35625

001010101.35000

001010111.34375

001011001.33750

001011011.33125

001011101.32500

001011111.31875

001100001.31250

001100011.30625

001100101.30000

001100111.29375

001101001.28750

001101011.28125

001101101.27500

001101111.26875

001110001.26250

001110011.25625

001110101.25000

001110111.24375

001111001.23750

001111011.23125

001111101.22500

001111111.21875

010000001.21250

010000011.20625

010000101.20000

010000111.19375

010001001.18750

010001011.18125

010001101.17500

010001111.16875

010010001.16250

010010011.15625

010010101.15000

010010111.14375

010011001.13750

010011011.13125

DAC

FN9236.0

February 6, 2006

Page 18

ISL6307A

TABLE 1. VID CODE (Continued)

VID4

VID7

800mV

VID6

400mV

VID5

200mV

100mV

VID3

50mV

VID2

25mV

VID1

12.5mV

VID0

6.25mV

VO LTAGE

010011101.12500

010011111.11875

010100001.11250

010100011.10625

010100101.10000

010100111.09375

010101001.08750

010101011.08125

010101101.07500

010101111.06875

010110001.06250

010110011.05625

010110101.05000

010110111.04375

010111001.03750

010111011.03125

010111101.02500

010111111.01875

011000001.01250

011000011.00625

011000101.00000

011000110.99375

011001000.98750

011001010.98125

011001100.97500

011001110.96875

011010000.96250

011010010.95625

011010100.95000

011010110.94375

011011000.93750

011011010.93125

011011100.92500

011011110.91875

011100000.91250

011100010.90625

011100100.90000

011100110.89375

011101000.88750

DAC

TABLE 1. VID CODE (Continued)

VID4

VID7

800mV

VID6

400mV

VID5

200mV

100mV

VID3

50mV

VID2

25mV

VID1

12.5mV

VID0

6.25mV

VO LTAGE

011101010.88125

011101100.87500

011101110.86875

011110000.86250

011110010.85625

011110100.85000

011110110.84375

011111000.83750

011111010.83125

011111100.82500

011111110.81875

100000000.81250

100000010.80625

100000100.80000

100000110.79375

100001000.78750

100001010.78125

100001100.77500

100001110.76875

100010000.76250

100010010.75625

100010100.75000

100010110.74375

100011000.73750

100011010.73125

100011100.72500

100011110.71875

100100000.71250

100100010.70625

100100100.70000

100100110.69375

100101000.68750

100101010.68125

100101100.67500

100101110.66875

100110000.66250

100110010.65625

100110100.65000

100110110.64375

DAC

FN9236.0

February 6, 2006

Page 19

ISL6307A

TABLE 1. VID CODE (Continued)

VID4

VID7

VID6

400mV

VID5

200mV

800mV

100111000.63750

100111010.63125

100111100.62500

100111110.61875

101000000.61250

101000010.60625

101000100.60000

101000110.59375

101001000.58750

101001010.58125

101001100.57500

101001110.56875

101010000.56250

101010010.55625

101010100.55000

101010110.54375

101011000.53750

101011010.53125

101011100.52500

101011110.51875

101100000.51250

101100010.50625

101100100.50000

11111110OFF

11111111OFF

100mV

VID3

50mV

VID2

25mV

VID1

12.5mV

VID0

6.25mV

DAC

VO LTAGE

In other cases, the designer may determine that a more cost-effective solution can be achieved by adding droop. Droop can help to reduce the output-voltage spike that results from fast load-current demand changes.

The magnitude of the spike is dictated by the ESR and ESL of the output capacitors selected. By positioning the no-load voltage level near the upper specification limit, a larger negative spike can be sustained without crossing the lower limit. By adding a well controlled output impedance, the output voltage under load can effectively be level shifted down so that a larger positive spike can be sustained without crossing the upper specification limit.

defined as

DROOPIAVGRFB

(EQ. 8)

The regulated output voltage is reduced by the droop voltage V

. The output voltage, as a function of load current, is

DROOP

derived by combining Equation 8 with the appropriate sample current expression defined by the current sense method employed.



OUT

OUTVREFVOFFSET

is the reference voltage and V

REF

offset voltage. I converter, R

–

is the total output current of the

OUT

is the sense resistor in the ISEN line, N is

ISEN

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

–=

 

the number of active channels, and R resistor. R R

SENSE

has a value of DCR, resistor or R

, depending on the sensing method.

------------------R R

ISEN

is the programmed

OFS

is the feedback

DS(ON)

(EQ. 9)

, or

Therefore, the equivalent load-line impedance, i.e. Droop impedance, is equal to:

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

------------------=

ISEN

(EQ. 10)

Output-Voltage Offset Programming

The ISL6307A allows the designer to accurately adjust the offset voltage. When a resistor, R OFS to VCC, the voltage across it is regulated to 1.6V. This causes a proportional current (I R

is connected to ground, the voltage across it is

OFS

regulated to 0.4V, and I between DAC and REF, R product (I

OFS

x R

OFS

flows out of OFS. A resistor

OFS

REF

) is equal to the desired offset voltage.

These functions are shown in Figure 9.

Once the desired output offset voltage has been determined, use the following formulas to set R

For Positive Offset (connect R

1.6 R

OFS

------------------------------=

OFFSET

REF

For Negative Offset (connect R

0.4 R

OFS

------------------------------=

OFFSET

REF

, is connected between

OFS

) to flow into OFS. If

OFS

, is selected so that the

OFS

to VCC):

OFS

to GND):

OFS

(EQ. 11)

(EQ. 12)

As shown in Figure 8, a current proportional to the average current in all active channels, I load-line regulation resistor, R across R

is proportional to the output current, effectively

, flows from FB through a

AVG

. The resulting voltage drop

creating an output voltage droop with a steady-state value

FN9236.0

February 6, 2006

Page 20

ISL6307A

DYNAMIC

VID D/A

E/A

1.6V +

VCC

FIGURE 9. OUTPUT VOLTAGE OFFSET PROGRAMMING

WITH ISL6307A

0.4V

GND

ISL6307ACR

DAC

VCC OR GND

OFS

REF

OFS

Dynamic VID

Modern microprocessors need to make changes to their core voltage as part of normal operation. They direct the core-voltage regulator to do this by making changes to the VID inputs during regulator operation. The power management solution is required to monitor the DAC inputs and respond to on-the-fly VID changes in a controlled manner. Supervising the safe output voltage transition within the DAC range of the processor without discontinuity or disruption is a necessary function of the core-voltage regulator.

of C

is based on the time duration for 1 bit VID change

REF

and the allowable delay time.

Assuming the microprocessor controls the VID change at 1 bit every T R

REF

REFRREFTVID

, the relationship between the time constant of

VID

and C

network and T

REF

is given by Equation 13.

VID

(EQ. 13)

Operation Initialization

Prior to converter initialization, proper conditions must exist on the enable inputs and VCC. When the conditions are met, the controller begins soft-start. Once the output voltage is within the proper window of operation, VR_RDY asserts a logic 1.

ISL6307A INTERNAL CIRCUIT

POR

CIRCUIT

SOFT-START

AND

FAULT LOGIC

ENABLE

COMPARATOR

0.875V

EXTERNAL CIRCUIT

VCC

EN_PWR

EN_VTT

+12V

10kΩ

910Ω

The ISL6307A checks the VID inputs six times every switching cycle. If the VID code is found to have been changed, the controller waits half of a complete cycle before executing a 12.5mV change. If during the half-cycle wait period, the difference between DAC level and the new VID code changes, no change is made. If the VID code is more than 1 bit higher or lower than the DAC (not recommended), the controller will execute 12.5mV changes six times per cycle until VID and DAC are equal. It is for this reason that it is important to carefully control the rate of VID stepping in 1bit increments.

In order to ensure the smooth transition of output voltage during VID change, a VID step change smoothing network composed of R

REF

and C

is required for an ISL6307A

REF

based voltage regulator (see Figure 8). The selection of R

is based on the desired offset as detailed above in

REF

Output-Voltage Offset Programming section. The selection

FIGURE 10. POWER SEQUENCING USING THRESHOLD-

SENSITIVE ENABLE (EN) FUNCTION

Enable and Disable

While in shutdown mode, the PWM outputs are held in a high-impedance state to assure the drivers remain off. The following input conditions must be met before the ISL6307A is released from shutdown mode.

1. The bias voltage applied at VCC must reach the internal power-on reset (POR) rising threshold. Once this threshold is reached, proper operation of all aspects of the ISL6307A is guaranteed. Hysteresis between the rising and falling thresholds assure that once enabled, the ISL6307A will not inadvertently turn off unless the bias voltage drops substantially (see Electrical Specifications).

2. The ISL6307A features an enable input (EN_PWR) for power sequencing between the controller bias voltage

FN9236.0

February 6, 2006

Page 21

ISL6307A

and another voltage rail. The enable comparator holds the ISL6307A in shutdown until the voltage at EN_PWR rises above 0.875V. The enable comparator has about 130mV of hysteresis to prevent bounce. It is important that the driver ICs reach their POR level before the ISL6307A becomes enabled. The schematic in Figure 10 illustrates the sequencing of the ISL6307A with the ISL66xx family of Intersil MOSFET drivers, which require 12V bias.

3. The voltage on EN_VTT must be higher than 0.875V to enable the controller. This pin is typically connected to the output of VTT VR.

When all conditions above are satisfied, ISL6307A begins the soft-start and ramps the output voltage to 1.1V first. After remaining at 1.1V for a fixed delay time, ISL6307A reads the VID code at the VID input pins. If the VID code is valid, ISL6307A will regulate the output to the final VID setting. If the VID code is an OFF code, ISL6307A will shut down. Cycling Vcc, EN_PWR or EN_VTT is needed to restart.

Soft-Start

ISL6307A based VR has four periods during soft-start, as shown in Figure 11. After Vcc, EN_VTT and EN_PWR reach their POR and enable thresholds, there’s a fixed delay period TD1. After this delay period, the VR will begin first soft-start ramp until the output voltage reaches 1.1V, Vboot voltage. Then, the controller will regulate the VR voltage at

1.1V for another fixed period, TD3. At the end of TD3 period, ISL6307A will read the VID signals. If the VID code is valid, ISL6307A will initiate the second soft-start ramp until the voltage reaches the VID voltage minus offset voltage.

The soft-start time is the sum of the four periods as shown in the following equation.

TD1TD2TD3TD4+++=

TD1 is the fixed delay with typical value as 1.36ms. TD3 is determined by the fixed 85µs time plus the time to obtain valid VID voltage. If the VID is valid before the output reaches the 1.1V, the minimum time to check the VID input is 500ns. Therefore, the minimum TD3 is about 86µs.

(EQ. 14)

VOUT, 500mV/DIV

VR_RDY, 5V/DIV

TD1 TD2 TD3

EN_VTT, 1V/DIV

500µs/DIV

FIGURE 11. SOFT-START WAVEFORMS

TD4

TD5

Fault Monitoring and Protection

The ISL6307A actively monitors output voltage and current to detect fault conditions. Fault monitors trigger protective measures to prevent damage to a microprocessor load. One common power good indicator is provided for linking to external system monitors. The schematic in Figure 12 outlines the interaction between the fault monitors and the power good signal, VR_RDY.

VR_RDY Signal

The VR_RDY pin is an open-drain logic output to indicate that the soft-start period has completed and the output voltage is within the regulated range. VR_RDY is pulled low during shutdown and releases high after a successful softstart and a delay time, TD5. TD5 is typically 85µs. VR_RDY will be pulled low when an undervoltage or overvoltage condition is detected, or the controller is disabled by a reset from EN_PWR, EN_VTT, POR, or a VID OFF-code.

During TD2 and TD4, ISL6307A digitally controls the DAC voltage change at 6.25mV per step. The time for each step is determined by the frequency of the soft-start oscillator which is defined by the resistor Rss from SS pin to GND. The two soft-start ramp times, TD2 and TD4, can be calculated based on the following equations.

1.1xR

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

TD2

TD4

6.25x25

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

VID

6.25x25

µs()=

1.1–()xR

(EQ. 15)

µs()=

(EQ. 16)

For example, when VID is set to 1.5V and Rss is set at 100kΩ, the first soft-start ramp time TD2 will be 704µs and the second soft-start ramp time TD4 will be 256µs.

FN9236.0

February 6, 2006

Page 22

VR_RDY

ISL6307A

voltage on EN_PWR, EN_VTT or VCC below the PORfalling threshold will reset the controller. Cycling the VID codes will not reset the controller.

100µA

50%

DAC

REFERENCE

SOFT-START, FAULT

AND CONTROL LOGIC

REPEAT FOR

EACH CHANNEL

OC1

AVG

100µA

AVG

IOUT

VDIFF

OC2

VID + 0.175V

FIGURE 12. POWER GOOD AND PROTECTION CIRCUITRY

IOUT

OVP

Undervoltage Detection

The undervoltage threshold is set at 50% of the VID voltage. When the output voltage at VSEN is below the undervoltage threshold, VR_RDY gets pulled low. When the output voltage comes back to 60% of the VID voltage, VR_RDY will return back to high.

Overvoltage Protection

Regardless of the VR being enabled or not, the over voltage protection (OVP) circuit will be active after its POR. The OVP thresholds are different under different operation conditions. When VR is not enabled and before the second soft-start, the OVP threshold is 1.275V. Once the controller detects a valid VID input, the OVP trip point will be changed to the VID voltage plus 175mV.

Overcurrent Protection

ISL6307A has two levels of overcurrent protection. Each phase is protected from a sustained overcurrent condition on a delayed basis, while the combined phase currents are protected on an instantaneous basis.

In instantaneous protection mode, the ISL6307A takes advantage of the proportionality between the load current and the average current, I condition. See the Channel-Current Balance section for more detail on how the average current is measured. The average current is continually compared with a constant 100µA reference current, as shown in Figure 12. Once the average current exceeds the reference current, a comparator triggers the converter to shutdown.

In individual overcurrent protection mode, the ISL6307A continuously compares the current of each channel with the same 100µA reference current. If any channel current exceeds the reference current continuously for eight consecutive cycles, the comparator triggers the converter to shutdown.

The overcurrent protection level for the above two OCP modes can be adjusted by changing the value of current sensing resistors. In addition, ISL6307A can also adjust the average OCP threshold level by adjusting the value of the resistor from IOUT to GND, as seen in Figure 12. This provides additional safety for the voltage regulator.

The following equation can be used to calculate the value of the resistor R

OCP2

IOUT

-------------------------------=

AVG OCP2,

based on the desired OCP level I

IOUT

, to detect an overcurrent

AVG

AVG,

(EQ. 17)

Two actions are taken by the ISL6307A to protect the microprocessor load when an overvoltage condition occurs.

At the inception of an overvoltage event, all PWM outputs are commanded low instantly (less than 20ns) until the voltage at VDIFF falls below 0.4V. This causes the Intersil drivers to turn on the lower MOSFETs and pull the output voltage below a level that might cause damage to the load. The PWM outputs remain low until VDIFF falls below 0.4V, and then PWM signals enter a high-impedance state. The Intersil drivers respond to the high-impedance input by turning off both upper and lower MOSFETs. If the overvoltage condition reoccurs, the ISL6307A will again command the lower MOSFETs to turn on. The ISL6307A will continue to protect the load in this fashion as long as the overvoltage condition recurs.

Once an overvoltage condition is detected, normal PWM operation ceases until the ISL6307A is reset. Cycling the

FN9236.0

February 6, 2006

Page 23

OUTPUT CURRENT, 50A/DIV

OUTPUT VOLTAGE, 500mV/DIV

ISL6307A

In normal operation, DRVEN remains low until ISL6307A begins soft-start ramp and then is pulled high (Figure 14). When an overcurrent event occurs, DRVEN is pulled low instantly, less than 20ns, to disable the driver so that both upper and lower FETs turn off (Figure 15). During an overvoltage condition, DRVEN remains high to allow the drivers to turn on the lower FETs to discharge the energy stored in the output inductor. Once the output voltage is reduced to 0.4V, DRVEN is pulled low, as shown in Figure 16.

DRVEN, 5V/DIV

FIGURE 13. OVERCURRENT BEHAVIOR IN HICCUP MODE.

= 500kHz

2ms/DIV

At the beginning of overcurrent shutdown, the controller places all PWM signals in a high-impedance state within 20ns, commanding the Intersil MOSFET driver ICs to turn off both upper and lower MOSFETs. The system remains in this state for a period of 4096 switching cycles. If the controller is still enabled at the end of this waiting period, it will attempt a soft-start. If the fault remains, the trip-retry cycles will continue indefinitely (as shown in Figure 13) until either the controller is disabled or the fault is cleared. Note, the energy delivered during trip-retry cycling is much less than during full-load operation. There is no thermal hazards during this kind of operation.

DRVEN, 5V/DIV

VOUT, 1V/DIV

OUTPUT CURRENT, 50A/DIV

OUTPUT VOLTAGE, 500mV/DIV

FIGURE 15. DRVEN DURING OVERCURRENT OPERATION

DRVEN, 5V/DIV

2ms/DIV

OUTPUT VOLTAGE, 500mV/DIV

EN, 5V/DIV

500µs/DIV

FIGURE 14. DRVEN WAVEFORM AT STARTUP

Driver Enable Output

The ISL6307A has a driver enable output pin, DRVEN. DRVEN is designed for applications where ISL6307A need to work with drivers that can not recognize three-state PWM input.

2ms/DIV

FIGURE 16. DRVEN DURING OVERVOLTAGE OPERATION

There’s no need to use DRVEN when ISL6307A is used with Intersil’s 12V drivers, such as ISL6612 and ISL6614. For drivers such as ISL6609 and ISL6605, DRVEN output of ISL6307A can be connected to the EN pin of the driver.

FN9236.0

February 6, 2006

Page 24

ISL6307A

Current Sense Output

The ISL6307A has two current sense output pins, IDROOP and IOUT and they are identical. In a typical application where load-line is required, the IDROOP pin is connected to the FB pin. The IOUT pin was designed for load current measurement. As shown in typical application schematics on pages 4 to 7, load current information can be obtained by measuring the voltage at IOUT pin with a resistor connected to ground. When the programmable temperature compensation function of ISL6307A is properly used, the output current at IOUT pin is proportional to load current, as shown in Figure 17.

V_IOUT, 200mV/DIV

Those numbers are recommended for accurate temperature compensation.

There are two comparators with hysteresis to compare the TM pin voltage to the fixed thresholds for VR_FAN and VR_HOT signals, respectively. VR_FAN is set high when TM is lower than 33% of Vcc, and is pulled to GND when TM increases to above 39% of Vcc. VR_HOT is set high when TM goes below 28% of Vcc, and is pulled to GND when TM goes back to above 33% of Vcc. Figure 20 shows operation of thermal monitoring and indication.

VCC

VR_FAN

TM1

NTC

0.33V

0.28V

VR_HOT

FIGURE 17. VOLTAGE AT IOUT PIN WITH ARESISTOR TO

GND WHEN LOAD CURRENT CHANGES

50A

100A

Thermal Monitoring (VR_HOT/VR_FAN)

There are two thermal signals to indicate the temperature status of the voltage regulator: VR_HOT and VR_FAN. Both VR_FAN and VR_HOT are open-drain outputs, and external pull-up resistors are required.

VR_FAN indicates that the temperature of the voltage regulator is high and more cooling airflow is needed. VR_HOT can be used to inform the system that the temperature of the voltage regulator is too high and the CPU should reduce its power consumption. VR_HOT may be tied to the CPU’s PROCHOT# signal.

The diagram of thermal monitoring function block is shown in Figure 18. One NTC resistor should be placed close to the power stage of the voltage regulator to sense the operational temperature, and one pull-up resistor is needed to form the voltage divider for the TM pin. As the temperature of the power stage increases, the resistance of the NTC will reduce, resulting in the reduced voltage at the TM pin. Figure 19 shows the TM voltage over temperature for a typical design with a recommended 6.8kΩ NTC (P/N: NTHS0805N02N6801 from Vishay) and 1kΩ resistor RTM1.

FIGURE 18. BLOCK DIAGRAM OF THERMAL MONITORING

FUNCTION

VTM / V

100%

90%

80%

70%

60%

/ V

50%

40%

30%

20%

0 20 40 60 80 100 120 140

FIGURE 19. THE RATIO OF TM VOLTAGE TO NTC

TEMPERATURE WITH RECOMMENDED PARTS

vs. Te m pe r ature

Temperature (

FN9236.0

February 6, 2006

Page 25

ISL6307A

compensate the temperature impact on the sensed current. The block diagram of this function is shown in Figure 21.

0.39*Vcc

0.33*Vcc

0.28*Vcc

VR_FAN

VR_HOT

T1 T2 T3

Temperature

FIGURE 20. VR_HOTAND VR_FAN SIGNAL VS TM VOLTAGE

Based on the NTC temperature characteristics and the desired threshold of VR_HOT, the pull-up resistor R

TM1

the TM pin is given by:

TM1

NTC(T3)

2.75xR

NTC T3()

(EQ. 18)

is the NTC resistance at the VR_HOT threshold

temperature T3.

The NTC resistance at the set point T2 and release point T1 of VR_FAN can be calculated as:

NTC T2()

1.267xR

NTC T3()

(EQ. 19)

TM1

Non-li near

NTC

TC1

TCOMP

TC2

A/ D

D/A

4-bit

A/ D

Channel current sense

Over current protection

Droop, I out &

sen6

sen5

sen4

sen3

sen2

sen1

FIGURE 21. BLOCK DIAGRAM OF INTEGRATED

TEMPERATURE COMPENSATION

When the TM NTC is placed close to the current sense component (inductor or MOSFET), the temperature of the NTC will track the temperature of the current sense component. Therefore, the TM voltage can be utilized to obtain the temperature of the current sense component.

NTC T1()

1.644xR

NTC T3()

(EQ. 20)

With the NTC resistance value obtained from Equations 19 & 20, the temperature T2 and T1 can be found from the NTC datasheet.

Temperature Compensation

ISL6307A supports inductor DCR sensing, MOSFET R inductor DCR and MOSFET R temperature coefficient, which is about +0.38%/°C. Because the voltage across the inductor or MOSFET is sensed for output current information, the sensed current has the same positive temperature coefficient as the inductor DCR or MOSFET R

In order to obtain the correct current information, there should be a way to correct the temperature impact on the current sense component. ISL6307A provides two methods: integrated temperature compensation and external temperature compensation.

Integrated Temperature Compensation

When TCOMP voltage is equal or greater than Vcc/15, ISL6307A will utilize the voltage at TM and TCOMP pins to

sensing, or resistive sensing techniques. Both

DS(ON)

have positive

ISL6307A converts the TM pin voltage to a 6-bit TM digital signal for temperature compensation. With the non-linear A/D converter of ISL6307A, TM digital signal is linearly proportional to the NTC temperature. For accurate temperature compensation, the ratio of the TM voltage to the NTC temperature of the practical design should be similar to that in Figure 19.

Depending on the location of the NTC and the air flow, the NTC may be cooler or hotter than the current sense component. TCOMP voltage can be utilized to correct the temperature difference between NTC and the current sense component. When a different NTC type or different voltage divider is used for the TM function, TCOMP voltage can also be used to compensate for the difference between the recommended TM voltage curve in Figure 20 and that of the actual design. ISL6307A converts the TCOMP pin voltage to a 4-bit TCOMP digital signal as the TCOMP factor N.

TCOMP factor N is an integer between 0 and 15. The integrated temperature compensation function is disabled for N = 0. For N = 4, the NTC temperature is equal to the temperature of the current sense component. For N < 4, the NTC is hotter than the current sense component. The NTC is cooler than the current sense component for N > 4. When N > 4, the larger the TCOMP factor N, the larger the difference between the NTC temperature and the temperature of the current sense component.

FN9236.0

February 6, 2006

Page 26

ISL6307A

ISL6307A multiplexes the TCOMP factor N with the TM digital signal to obtain the adjustment gain to compensate the temperature impact on the sensed channel current. The compensated channel current signal is used for droop and overcurrent protection functions.

Design procedure:

1. Properly choose the voltage divider for TM to match the TM voltage vs. temperature curve with the recommended curve in Figure 19.

2. Run the actual board under the full load and the desired cooling conditions.

3. After the board reaches the thermal steady state, record the temperature (T (inductor or MOSFET) and TM voltage and Vcc.

4. Use the following equation to calculate the resistance of the TM NTC, and find out the corresponding NTC temperature T

NTC T

()

NTC

VTMxR

--------------------------------=

VCCV–

5. Use the following equation to calculate the TCOMP factor N.

CSC

NTC

T–

400+

NTC

()

209x T

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

3xT

6. Choose an integral number close to the above result for the TCOMP factor. If this factor is higher than 15, use N=15. If it is less than 1, use N=1.

7. Choose the pull-up resistor R

8. If N=15, do not use the pull-down resistor R Otherwise obtain R

) of the current sense component

CSC

from the NTC datasheet.

TM1

4+=

(typical 10kΩ).

TC1

by the following equation.

TC2

TC2.

(EQ. 21)

(EQ. 22)

an external temperature compensation network, as shown in Figure 22, can be used to cancel the temperature impact on the droop (i.e. load-line).

C2 (OPTIONAL)

DROOP

EXTERNAL TCOMP

COMPENSATION

NETWORK

NTC

FIGURE 22. TEMPERATURE COMPENSATION WITH

EXTERNAL NTC NETWORK

COMP

IDROOP

ISL6307A

VDIFF

The sensed current will flow out of the IDROOP pin and develop the droop voltage across the resistor, R FB and VDIFF. If R

resistance reduces as the temperature

FB,

between

increases, the temperature impact on the droop can be compensated. An NTC resistor can be placed close to the power stage and used to form R

. Due to the non-linear

temperature characteristics of the NTC, a resistor network is needed to make the equivalent resistance between FB and VDIFF pins reverse proportional to the temperature.

The external temperature compensation network can only compensate the temperature impact on the droop, while it has no impact to the sensed current inside ISL6307A. Therefore this network cannot compensate for the temperature impact on the over current protection function.

TC2

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

15 N–

(EQ. 23)

NxR

TC1

9. Run the actual board under full load again with the proper resistors to TCOMP.

10. Record the output voltage as V1 immediately after the output voltage is stable with the full load. Record the output voltage as V2 after the VR reaches the thermal steady state.

11. If the output voltage increases over 2mV as the temperature increases, i.e. V2-V1>2mV, reduce N and redesign R

. If the output voltage decreases over 2mV

TC2

as the temperature increases, i.e. V1-V2>2mV, increase N and redesign R

TC2

The design spreadsheet is available for those calculations. Please contact Intersil to get the spreadsheet.

External Temperature Compensation

By setting the voltage of TCOMP to 0, the integrated temperature compensation function is disabled. In this case,

To simplify the design for external NTC network parameters, Excel calculation tools have been developed. Please contact Intersil to get the tools.

General Design Guide

This design guide is intended to provide a high-level explanation of the steps necessary to create a multiphase power converter. It is assumed that the reader is familiar with many of the basic skills and techniques referenced below. In addition to this guide, Intersil provides complete reference designs that include schematics, bills of materials, and example board layouts for all common microprocessor applications.

Power Stages

The first step in designing a multiphase converter is to determine the number of phases. This determination depends heavily on the cost analysis which in turn depends on system constraints that differ from one design to the next. Principally, the designer will be concerned with whether components can be mounted on both sides of the circuit

FN9236.0

February 6, 2006

Page 27

ISL6307A

board; whether through-hole components are permitted; and the total board space available for power-supply circuitry. Generally speaking, the most economical solutions are those in which each phase handles between 20 and 30A. All surface-mount designs will tend toward the lower end of this current range. If through-hole MOSFETs and inductors can be used, higher per-phase currents are possible. In cases where board space is the limiting constraint, current can be pushed as high as 40A per phase, but these designs require heat sinks and forced air to cool the MOSFETs, inductors and heat-dissipating surfaces.

MOSFETS

The choice of MOSFETs depends on the current each MOSFET will be required to conduct; the switching frequency; the capability of the MOSFETs to dissipate heat; and the availability and nature of heat sinking and air flow.

LOWER MOSFET POWER CALCULATION

The calculation for heat dissipated in the lower MOSFET is simple, since virtually all of the heat loss in the lower MOSFET is due to current conducted through the channel resistance (R continuous output current; I current (see Equation 1); d is the duty cycle (V

). In Equation 24, IM is the maximum

DS(ON)

is the peak-to-peak inductor

OUT/VIN

); and

L is the per-channel inductance.

LOW 1,

DS ON()





-----N



1d–()

LPP,

--------------------------------+=

1d–()

(EQ. 24)

An additional term can be added to the lower-MOSFET loss equation to account for additional loss accrued during the dead time when inductor current is flowing through the lower-MOSFET body diode. This term is dependent on the diode forward voltage at I frequency, f

; and the length of dead times, td1 and td2, at

, V

; the switching

D(ON)

the beginning and the end of the lower-MOSFET conduction interval respectively.

LOW 2,

DON()fS



------

---------+







------



–

--------2

(EQ. 25)

Thus the total maximum power dissipated in each lower MOSFET is approximated by the summation of P P

LOW,2

LOW,1

and

UPPER MOSFET POWER CALCULATION

In addition to R

losses, a large portion of the upper-

DS(ON)

MOSFET losses are due to currents conducted across the input voltage (V

) during switching. Since a substantially

higher portion of the upper-MOSFET losses are dependent on switching frequency, the power calculation is more complex. Upper MOSFET losses can be divided into separate components involving the upper-MOSFET switching times; the lower-MOSFET body-diode reverserecovery charge, Q

; and the upper MOSFET R

DS(ON)

conduction loss.

When the upper MOSFET turns off, the lower MOSFET does not conduct any portion of the inductor current until the voltage at the phase node falls below ground. Once the lower MOSFET begins conducting, the current in the upper MOSFET falls to zero as the current in the lower MOSFET ramps up to assume the full inductor current. In Equation 26, the required time for this commutation is t approximated associated power loss is P

≈

UP 1,VIN



------



---------+



----





and the

UP,1

(EQ. 26)

At turn on, the upper MOSFET begins to conduct and this transition occurs over a time t approximate power loss is P

≈

UP 2,VIN



------





--------2

----





–

. In Equation 27, the

UP,2

(EQ. 27)

A third component involves the lower MOSFET’s reverserecovery charge, Qrr. Since the inductor current has fully commutated to the upper MOSFET before the lowerMOSFET’s body diode can draw all of Q

, it is conducted

through the upper MOSFET across VIN. The power dissipation, P

≈

UP 3,VINQrrfS

, can be calculated from Equation 28.

UP,3

(EQ. 28)

approximately

Finally, the resistive part of the upper MOSFET’s is given in Equation 29 as P

UP 4,rDS ON()

UP,4





-----N



d+≈

---------12

(EQ. 29)

The total power dissipated by the upper MOSFET, at full load, can now be approximated as the summation of the results from Equations 26, 27, 28 and 29. Since the power equations depend on the MOSFET parameters, choosing the correct MOSFETs, can be an iterative process involving repetitive solutions to the loss equations for different MOSFETs and different switching frequencies.

Current Sensing Resistor

The resistors connected between these ISEN+ pins and the respective phase nodes (R side of inductor (DCR sensing) determine the gains in the load-line regulation loop and the channel-current balance loop as well as setting the overcurrent trip point. Select values for these resistors based on the room temperature R

of the lower MOSFETs, the DCR of inductor or

DS(ON)

additional resistor; the full-load operating current, I the number of phases, N, using Equation 30.

ISEN

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

50 10

--------=

–

Sensing) or the output

DS(ON)

; and

(EQ. 30)

FN9236.0

February 6, 2006

Page 28

ISL6307A

In certain circumstances, it may be necessary to adjust the value of one or more ISEN resistors. When the components of one or more channels are inhibited from effectively dissipating their heat so that the affected channels run hotter than desired, choose new, smaller values of RISEN for the affected phases (see the section entitled Channel-Current Balance). Choose R

in proportion to the desired

ISEN,2

decrease in temperature rise in order to cause proportionally less current to flow in the hotter phase.

∆T

ISEN 2,

ISEN

In Equation 31, make sure that ∆T

----------= ∆T

is the desired temperature

rise above the ambient temperature, and ∆T

is the measured

(EQ. 31)

temperature rise above the ambient temperature. While a single adjustment according to Equation 31 is usually sufficient, it may occasionally be necessary to adjust R

ISEN

two or more times to achieve optimal thermal balance between all channels.

Load-Line Regulation Resistor

The load-line regulation resistor is labelled RFB in Figure 8. Its value depends on the desired full-load droop voltage (V

in Figure 8). If Equation 30 is used to select each

DROOP

ISEN resistor, the load-line regulation resistor is as shown in Equation 32.

DROOP

-------------------------=

50 106–×

(EQ. 32)

If one or more of the ISEN resistors are adjusted for thermal balance, as in Equation 31, the load-line regulation resistor should be selected according to Equation 33 where I full-load operating current and R connected to the n

DROOP

-------------------------------- R

IFLr

DS ON()

ISEN pin.

∑

ISEN n()

is the ISEN resistor

ISEN(n)

is the

(EQ. 3

Compensation

The two opposing goals of compensating the voltage regulator are stability and speed. Depending on whether the regulator employs the optional load-line regulation as described in Load-Line Regulation, there are two distinct methods for achieving these goals.

The final locations of these poles are determined by the system function, the gain of the current signal, and the value of the compensation components, R

and CC.

Since the system poles and zero are affected by the values of the components that are meant to compensate them, the solution to the system equation becomes fairly complicated. Fortunately there is a simple approximation that comes very close to an optimal solution. Treating the system as though it were a voltage-mode regulator by compensating the L-C poles and the ESR zero of the voltage-mode approximation yields a solution that is always stable with very close to ideal transient performance.

C2 (OPTIONAL)

DROOP

FIGURE 23. COMPENSATION CONFIGURATION FOR

LOAD-LINE REGULATED ISL6307A CIRCUIT

The feedback resistor, R

COMP

IDROOP

ISL6307A

VDIFF

, has already been chosen as outlined in Load-Line Regulation Resistor. Select a target bandwidth for the compensated system, f

. The target

bandwidth must be large enough to assure adequate transient performance, but smaller than 1/3 of the perchannel switching frequency. The values of the compensation components depend on the relationships of f to the L-C pole frequency and the ESR zero frequency. For each of the three cases which follow, there are a separate set of equations for the compensation components

------------------- f

Case 1:

2π LC

CRFB

2π f0VppLC

------------------------------------=

0.75V

------------------------------------= 2π VPPRFBf

COMPENSATING LOAD-LINE REGULATED CONVERTER

The load-line regulated converter behaves in a similar manner to a peak-current mode controller because the two poles at the output-filter L-C resonant frequency split with the introduction of current information into the control loop.

FN9236.0

February 6, 2006

Page 29

ISL6307A

Case 2:

Case 3:

------------------2π LC

CRFB

-------------------------------------------------------------=

2π()2f

------------------------------>

2π C ESR()

CRFB

0.75VINESR()C

-------------------------------------------------=

2π V

In Equation 34, L is the per-channel filter inductance divided

------------------------------<≤ 2π CESR()

VPP2π()2f

--------------------------------------------=

0.75 V

0.75V

VPPRFBLC

2π f0VppL

------------------------------------------=

0.75 V

PPRFBf0

ESR()

(EQ. 34)

by the number of active channels; C is the sum total of all output capacitors; ESR is the equivalent-series resistance of the bulk output-filter capacitance; and V

is the peak-to-

peak sawtooth signal amplitude as described in Figure 7 and Electrical Specifications.

The optional capacitor C

, is sometimes needed to bypass

noise away from the PWM comparator (see Figure 24). Keep a position available for C

, and be prepared to install a high-

frequency capacitor of between 22pF and 150pF in case any leading-edge jitter problem is noted.

Once selected, the compensation values in Equation 34 assure a stable converter with reasonable transient performance. In most cases, transient performance can be improved by making adjustments to R value of R

while observing the transient performance on an

. Slowly increase the

oscilloscope until no further improvement is noted. Normally, C

will not need adjustment. Keep the value of CC from

Equation 34 unless some performance issue is noted.

COMPENSATION WITHOUT LOAD-LINE REGULATION

The non load-line regulated converter is accurately modeled as a voltage-mode regulator with two poles at the L-C resonant frequency and a zero at the ESR frequency. A

type III controller, as shown in Figure 24, provides the necessary compensation.

FIGURE 24. COMPENSATION CIRCUIT FOR ISL6307A BASED

CONVERTER WITHOUT LOAD-LINE REGULATION

The first step is to choose the desired bandwidth, f

COMP

IDROOP

VDIFF

ISL6307A

, of the

compensated system. Choose a frequency high enough to assure adequate transient performance but not higher than 1/3 of the switching frequency. The type-III compensator has an extra high-frequency pole, f

. This pole can be used for

added noise rejection or to assure adequate attenuation at the error-amplifier high-order pole and zero frequencies. A good general rule is to choose f higher if desired. Choosing f

=10f0, but it can be

to be lower than 10f0 can

cause problems with too much phase shift below the system bandwidth.

In the solutions to the compensation equations, there is a single degree of freedom. For the solutions presented in Equation 35, R

is selected arbitrarily. The remaining

compensation components are then selected according to Equation 35.

C ESR()

-----------------------------------------=

LC C ESR()–

-----------------------------------------=

LC C ESR()–

R1R

0.75V

--------------------------------------------------------------- ----=

2π()2f0fHFLCRFBV

VPP2π

------------------------------------------------------------- --------=

0.75 V

0.75V

------------------------------------------------------------- ------=

2π()

 

f0fHFLCRFBV

f0fHFLCR



2π fHFLC 1–





2π fHFLC 1–



(EQ. 35)

In Equation 35, L is the per-channel filter inductance divided by the number of active channels; C is the sum total of all

FN9236.0

February 6, 2006

Page 30

ISL6307A

output capacitors; ESR is the equivalent-series resistance of the bulk output-filter capacitance; and V

is the peak-to-

peak sawtooth signal amplitude as described in Figure 7 and Electrical Specifications.

Output Filter Design

The output inductors and the output capacitor bank together form a low-pass filter responsible for smoothing the pulsating voltage at the phase nodes. The output filter also must provide the transient energy until the regulator can respond. Because it has a low bandwidth compared to the switching frequency, the output filter necessarily limits the system transient response. The output capacitor must supply or sink load current while the current in the output inductors increases or decreases to meet the demand.

In high-speed converters, the output capacitor bank is usually the most costly (and often the largest) part of the circuit. Output filter design begins with minimizing the cost of this part of the circuit. The critical load parameters in choosing the output capacitors are the maximum size of the load step, ∆I; the load-current slew rate, di/dt; and the maximum allowable output-voltage deviation under transient loading, ∆V their capacitance, ESR, and ESL (equivalent series inductance).

. Capacitors are characterized according to

MAX

are selected, the maximum allowable ripple voltage, V

PP(MAX)

L ESR()

, determines the lower limit on the inductance.



–



------------------------------------------------------------≥

fSVINV

OUT

PP MAX()

(EQ. 37)

Since the capacitors are supplying a decreasing portion of the load current while the regulator recovers from the transient, the capacitor voltage becomes slightly depleted. The output inductors must be capable of assuming the entire load current before the output voltage decreases more than ∆V

. This places an upper limit on inductance.

MAX

Equation 38 gives the upper limit on L for the cases when the trailing edge of the current transient causes a greater output-voltage deviation than the leading edge. Equation 39 addresses the leading edge. Normally, the trailing edge dictates the selection of L because duty cycles are usually less than 50%. Nevertheless, both inequalities should be evaluated, and L should be selected based on the lower of the two results. In each equation, L is the per-channel inductance, C is the total output capacitance, and N is the number of active channels.

2NCV

--------------------- ∆V

()

∆I

MAX

∆I ESR()–≤

(EQ. 38)

At the beginning of the load transient, the output capacitors supply all of the transient current. The output voltage will initially deviate by an amount approximated by the voltage drop across the ESL. As the load current increases, the voltage drop across the ESR increases linearly until the load current reaches its final value. The capacitors selected must have sufficiently low ESL and ESR so that the total outputvoltage deviation is less than the allowable maximum. Neglecting the contribution of inductor current and regulator response, the output voltage initially deviates by an amount

∆V ESL()

-----ESR()∆I+≈ dt

(EQ. 36)

The filter capacitor must have sufficiently low ESL and ESR so that ∆V < ∆V

MAX

Most capacitor solutions rely on a mixture of high-frequency capacitors with relatively low capacitance in combination with bulk capacitors having high capacitance but limited high-frequency performance. Minimizing the ESL of the high-frequency capacitors allows them to support the output voltage as the current increases. Minimizing the ESR of the bulk capacitors allows them to supply the increased current with less output voltage deviation.

The ESR of the bulk capacitors also creates the majority of the output-voltage ripple. As the bulk capacitors sink and source the inductor ac ripple current (see Interleaving and Equation 2), a voltage develops across the bulk-capacitor ESR equal to I

(ESR). Thus, once the output capacitors

C,PP

()

1.25

≤

-------------------------- ∆ V

()

∆I

∆IESR()– VINVO–

MAX

 

(EQ. 39)

Switching Frequency

There are a number of variables to consider when choosing the switching frequency, as there are considerable effects on the upper-MOSFET loss calculation. These effects are outlined in MOSFETs, and they establish the upper limit for the switching frequency. The lower limit is established by the requirement for fast transient response and small outputvoltage ripple as outlined in Output Filter Design. Choose the lowest switching frequency that allows the regulator to meet the transient-response requirements.

Switching frequency is determined by the selection of the frequency-setting resistor, R

(see the figures labelled

Typical Application on pages 4, 5, 6 and 7). Equation 40 is provided to assist in selecting the correct value for R

2.5X10

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

600–=

(EQ. 40)

Input Capacitor Selection

The input capacitors are responsible for sourcing the AC component of the input current flowing into the upper MOSFETs. Their RMS current capacity must be sufficient to handle the AC component of the current drawn by the upper MOSFETs that is related to duty cycle and the number of active phases.

FN9236.0

February 6, 2006

Page 31

ISL6307A

0.3

)

RMS

0.2

0.1

= 0

L,PP

= 0.5 I

L,PP

INPUT-CAPACITOR CURRENT (I

L,PP

00.4 1.00.2 0.6 0.8

= 0.75 I

DUTY CYCLE (V

O/VIN

)

FIGURE 25. NORMALIZED INPUT-CAPACITOR RMS CURRENT

vs DUTY CYCLE FOR 2-PHASE CONVERTER

0.3 I

= 0

L,PP

)

RMS/

0.2

0.1

INPUT-CAPACITOR CURRENT (I

= 0.25 I

L,PP

00.4 1.00.2 0.6 0.8

= 0.5 I

L,PP

DUTY CYCLE (VO/VIN)

= 0.75 I

FIGURE 26. NORMALIZED INPUT-CAPACITOR RMS CURRENT

vs DUTY CYCLE FOR 3-PHASE CONVERTER

on and off. Select low ESL ceramic capacitors and place one as close as possible to each upper MOSFET drain to minimize board parasitic impedances and maximize suppression.

0.3 I

= 0

L,PP

)

RMS/

INPUT-CAPACITOR CURRENT (I

= 0.25 I

L,PP

0.2

0.1

00.4 1.00.2 0.6 0.8

= 0.5 I

L,PP

= 0.75 I

L,PP

DUTY CYCLE (V

O/VIN

)

FIGURE 27. NORMALIZED INPUT-CAPACITOR RMS CURRENT

vs DUTY CYCLE FOR 4-PHASE CONVERTER

MULTIPHASE RMS IMPROVEMENT

Figure 28 is provided as a reference to demonstrate the dramatic reductions in input-capacitor RMS current upon the implementation of the multiphase topology. For example, compare the input RMS current requirements of a two-phase converter versus that of a single phase. Assume both converters have a duty cycle of 0.25, maximum sustained output current of 40A, and a ratio of I

to IO of 0.5. The

L,PP

single phase converter would require 17.3Arms current capacity while the two-phase converter would only require

10.9Arms. The advantages become even more pronounced when output current is increased and additional phases are added to keep the component cost down relative to the single phase approach.

For a two phase design, use Figure 25 to determine the input-capacitor RMS current requirement given the duty cycle, maximum sustained output current (I of the per-phase peak-to-peak inductor current (I

), and the ratio

L,PP

) to IO. Select a bulk capacitor with a ripple current rating which will minimize the total number of input capacitors required to support the RMS current calculated. The voltage rating of the capacitors should also be at least 1.25 times greater than the maximum input voltage.

Figures 26 and 27 provide the same input RMS current information for three and four phase designs respectively. Use the same approach to selecting the bulk capacitor type and number as described above.

Low capacitance, high-frequency ceramic capacitors are needed in addition to the bulk capacitors to suppress leading and falling edge voltage spikes. This is a result from the high current slew rates produced by the upper MOSFETs turning

FN9236.0

February 6, 2006

Page 32

ISL6307A

0.6

)

RMS/

0.4

0.2

= 0

L,PP

= 0.5 I

L,PP

INPUT-CAPACITOR CURRENT (I

00.4 1.00.2 0.6 0.8

FIGURE 28. NORMALIZED INPUT-CAPACITOR RMS

L,PP

CURRENT vs DUTY CYCLE FOR SINGLE-PHASE CONVERTER

= 0.75 I

DUTY CYCLE (V

)

O/VIN

Layout Considerations

The following layout strategies are intended to minimize the impact of board parasitic impedances on converter performance and to optimize the heat-dissipating capabilities of the printed-circuit board. These sections highlight some important practices which should not be overlooked during the layout process.

placement. Critical small signal components to place close to the controller include the ISEN resistors, R

resistor,

feedback resistor, and compensation components.

Bypass capacitors for the ISL6307A and ISL66XX driver bias supplies must be placed next to their respective pins. Trace parasitic impedances will reduce their effectiveness.

Plane Allocation and Routing

Dedicate one solid layer, usually a middle layer, for a ground plane. Make all critical component ground connections with vias to this plane. Dedicate one additional layer for power planes; breaking the plane up into smaller islands of common voltage. Use the remaining layers for signal wiring.

Route phase planes of copper filled polygons on the top and bottom once the switching component placement is set. Size the trace width between the driver gate pins and the MOSFET gates to carry 4A of current. When routing components in the switching path, use short wide traces to reduce the associated parasitic impedances.

Component Placement

Within the allotted implementation area, orient the switching components first. The switching components are the most critical because they carry large amounts of energy and tend to generate high levels of noise. Switching component placement should take into account power dissipation. Align the output inductors and MOSFETs such that spaces between the components are minimized while creating the PHASE plane. Place the Intersil MOSFET driver IC close to the MOSFETs they control, to reduce the parasitic impedances due to trace length between critical driver input and output signals. If possible, duplicate the same placement of these components for each phase.

Next, place the input and output capacitors. Position one high-frequency ceramic input capacitor next to each upper MOSFET drain. Place the bulk input capacitors as close to the upper MOSFET drains as dictated by the component size and dimensions. Long distances between input capacitors and MOSFET drains result in too much trace inductance and a reduction in capacitor performance. Locate the output capacitors between the inductors and the load, while keeping them in close proximity to the microprocessor socket.

The ISL6307A can be placed off to one side or centered relative to the individual phase switching components. Routing of sense lines and PWM signals will guide final

FN9236.0

February 6, 2006

Page 33

ISL6307A

Quad Flat No-Lead Plastic Package (QFN) Micro Lead Frame Plastic Package (MLFP)

L48.7x7

48 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE (COMPLIANT TO JEDEC MO-220VKKD-2 ISSUE C)

MILLIMETERS

SYMBOL

A 0.80 0.90 1.00 A1 - - 0.05 A2 - - 1.00 9 A3 0.20 REF 9

b 0.18 0.23 0.30 5, 8

D 7.00 BSC D1 6.75 BSC 9 D2 4.15 4.30 4.45 7, 8

E 7.00 BSC E1 6.75 BSC 9 E2 4.15 4.30 4.45 7, 8

e 0.50 BSC k0.25 - - L 0.30 0.40 0.50 8

L1 - - 0.15 10

N482 Nd 12 3 Ne 12 3

P- -0.609

θ --129

NOTES:

1. Dimensioning and tolerancing conform to ASME Y14.5-1994.

2. N is the number of terminals.

3. Nd and Ne refer to the number of terminals on each D and E.

4. All dimensions are in millimeters. Angles are in degrees.

5. Dimension b applies to the metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip.

6. The configuration of the pin #1 identifier is optional, but must be located within the zone indicated. The pin #1 identifier may be either a mold or mark feature.

7. Dimensions D2 and E2 are for the exposed pads which provide improved electrical and thermal performance.

8. Nominal dimensions are provided to assist with PCB Land Pattern Design efforts, see Intersil Technical Brief TB389.

9. Features and dimensions A2, A3, D1, E1, P & θ are present when Anvil singulation method is used and not present for saw singulation.

10. Depending on the method of lead termination at the edge of the package, a maximum 0.15mm pull back (L1) maybe present. L minus L1 to be equal to or greater than 0.3mm.

NOTESMIN NOMINAL MAX

Rev. 1 10/02

All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.

Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality

Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.

For information regarding Intersil Corporation and its products, see www.intersil.com

FN9236.0

February 6, 2006

Datasheets isl6307a Datasheet

Specifications and Main Features

Frequently Asked Questions

User Manual