IR3523

Page 11 of 37

June 20, 2008

SYSTEM THEORY OF OPERATION

PWM Control Method

The PWM block diagram of the xPHASE3

with trailing edge modulation is used. A high-gain wide-bandwidth voltage type error amplifier in the Control IC is

used for the voltage control loop. Input voltage is sensed in phase ICs and feed-forward control is realized. The

PWM ramp slope will change with the input voltage automatically compensating for changes in the input voltage.

The input voltage can change due to variations in the silver box output voltage or due to the wire and PCB-trace

voltage drop related to changes in load current.

Figure 5 - PWM Block Diagram

Frequency and Phase Timing Control

The oscillator is located in the Control IC and the system clock frequency is programmable from 500kHz to 9MHZ

by an external resistor. The control IC system clock signal (CLKOUT) is connected to CLKIN of all the phase ICs.

The phase timing of the phase ICs is controlled by the daisy chain loop, where control IC phase clock output

(PHSOUT) is connected to the phase clock input (PHSIN) of the first phase IC, and PHSOUT of the first phase IC is

connected to PHSIN of the second phase IC, etc. and PHSOUT of the last phase IC is connected back to PHSIN of

the control IC. During power up, the control IC sends out clock signals from both CLKOUT and PHSOUT pins and

detects the feedback at PHSIN pin to determine the phase number and monitor any fault in the daisy chain loop.

Figure 6 shows the phase timing for a four phase converter.

GND

VOUT1

VOSNS1+

DACIN

VCC

VDAC1

VOUT1

IIN1

VDRP1

LGND

ISHARE

PHSIN

VOSNS1-

CSIN-

CSIN+

GATEL

EAIN

GATEH

SW

VIN

FB1

EAOUT1

CLKOUT

CLKIN

PHSOUT

PGND

VCCL

VCCH

DACIN

VCC

CLKIN

PHSOUT

CSIN+

GATEL

EAIN

GATEH

ISHARE

PHSIN

SW

PGND

VCCL

VCCH

CSIN-

PHSIN

PHSOUT

VID6

VID6

IROSC

VID6

VID6

VID6

VID6

VID6

VID6

VID6

VID6

GATE DRIVE

VOLTAGE

-

+

+

+

ENABLE

RAMP

DISCHARGE

CLAMP

BODY

BRAKING

COMPARATOR

IFB1

VDRP1 AMP

VDAC

CLOCK GENERATOR

CURRENT

SENSE

AMPLIFIER

R

S

SHARE ADJUST

ERROR AMPLIFIER

RESET

DOMINANT

PWM

LATCH

ERROR

AMPLIFIER

COUT

IR3523 CONTROL IC

PHASE IC

Output 1 Only

PWM

COMPARATOR

PWM

COMPARATOR

-

+

+

+

RAMP

DISCHARGE

CLAMP

ENABLE

BODY

BRAKING

COMPARATOR

SHARE ADJUST

ERROR AMPLIFIER

RESET

DOMINANT

PWM

LATCH

CURRENT

SENSE

AMPLIFIER

R

S

PHASE IC

REMOTE SENSE

AMPLIFIER

CCS RCS

+

-

CFB1

RCS

CBST

+

-

CCS

CBST

+

-

+

-

CCP11

+

-

+

-

RFB12

RDRP1

CDRP1

RFB11

3K

+

-

+

-

CLK

D

Q

+

-

+

-

RCP1

+

-

3K

+

-

+

-

CCP12

CLK

D

Q

+

-