IR3094PBF

Page 11 of 29

09/26/05

PWM Operation

The IR3094 is a fully integrated 3 phase interleaved PWM control IC which uses voltage mode control with trailing

edge modulation. A high-gain wide-bandwidth voltage type Error Amplifier in the Control IC is used for the voltage

control loop. The PWM block diagram of the IR3094 is shown in Figure 2.

S

Q

QB

R

OVP LATCH

CSINM2

CSINM1

9p

9p

VDRP BUFFER

RESET DOMINANT

RESET DOMINANT

0.575V

IROSC

-

+

PWM COMPARATOR

0 TO IROSC*3/4

+

-

Share Adjust Error Amp

IROSC

ERROR AMPLIFIER

0.6V

RCS2

S

Q

QB

R

RSFF

CSC2

IROSC/2

CCS1

1

2

-

+

PWM COMPARATOR

CCS2

RSC2

RCS1

CCOMP

CDAC

VDAC

0% DUTY CYCLE

RFB

CLK2

S

Q

QB

R

RSFF

RDRP

RCOMP

RDAC

0.6V

COUT

1

2

VREF

VDRP

EAOUT

SCOMP2

GATEL1

GATEH1

GATEH2

CSINP1

GATEL2

CSINP2

CSINM3

FB

VOSNS-

VOUT SENSE+

VOUT SENSE-

VOUT-

VOUT+

VDAC

-

+

X23.5

CSINP3

RESET DOMINANT

9p

IROSC

-

+

PWM COMPARATOR

0 TO IROSC*3/4

+

-

Share Adjust Error Amp

S

Q

QB

R

RSFF

0.6V

RCS3 CCS3

1

2

GATEH3

GATEL3

VIN

CSC3

SCOMP3

RSC3

VIN

VIN

VDAC

-

+

X23.5

VDAC

-

+

X23.5

CLK3

CLK2

EAOUT

CLK1

CLK2

IROSC

CLK3

U30

OSCBLOCK

CLK3

OVP SET

OVP RESET

Figure 2 – PWM Block Diagram

Refer to Figure 3. Upon receiving a clock pulse, the RSFF is set, the internal PWM ramp voltage begins to

increase, the low side driver is turned off, and the high side driver is then turned on. For phase 1, an internal 9pf

capacitor is charged by a current source that proportional to the switching frequency resulting in a ramp rate of

50mV per percent duty cycle. For example, if the steady-state operating switch node duty cycle is 10%, then the

internal ramp amplitude is typically 500mV from the starting point (or floor) to the crossing of the EAOUT control

voltage. When the PWM ramp voltage exceeds the Error Amplifier’s output voltage, the RSFF is reset. This turns

off the high side driver, turns on the low side driver, and discharges the PWM ramp to 0.6V until the next clock

pulse.