IR3081M International Rectifier, IR3081M Datasheet - Page 7

• Manufacturer Part Number: IR3081M
• Description: IC PHASE CONTROLLER 28-MLPQ
• Manufacturer: International Rectifier
• Series: XPhase™r

Specifications of IR3081M

• Applications: Processor
• Current - Supply: 11mA
• Voltage - Supply: 9.5 V ~ 14 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 28-MLPQ
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *IR3081M

PWM Control Method
The PWM block diagram of the XPhase
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. An external RC circuit connected to the input voltage and ground is used to program the
slope of the PWM ramp and to provide the feed-forward control at each phase. The PWM ramp slope will change
with the input voltage and automatically compensate 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.
Frequency and Phase Timing Control
The oscillator is located in the Control IC and its frequency is programmable from 150kHz to 1MHZ by an external
resistor. The output of the oscillator is a 50% duty cycle triangle waveform with peak and valley voltages of
approximately 5V and 1V respectively. This signal is used to program both the switching frequency and phase
timing of the Phase ICs. The Phase IC is programmed by resistor divider R
VBIAS reference voltage and the Phase IC LGND pin. A comparator in the Phase ICs detects the crossing of the
oscillator waveform over the voltage generated by the resistor divider and triggers a clock pulse that starts the PWM
cycle. The peak and valley voltages track the VBIAS voltage reducing potential Phase IC timing errors. Figure 3
shows the Phase timing for an 8 phase converter. Note that both slopes of the triangle waveform can be used for
phase timing by swapping the RMPIN+ and RMPIN– pins, as shown in Figure 2.
+
-
50%
DUTY
CYCLE
Page 7 of 39
VBIAS
REGULATOR
CONTROL IC
RAMP GENERATOR
IFB
+
-
ERROR
AMP
IROSC
VDAC
VPEAK
VVALLEY
+
-
VDRP
AMP
VDRP
IIN
RMPOUT
VBIAS
VDAC
VOSNS-
EAOUT
FB
RVFB
RDRP
TM
Figure 2. PWM Block Diagram
architecture is shown in Figure 2. Feed-forward voltage mode control with
RPWMRMP
CPWMRMP
RPWMRMP
CPWMRMP
RPHS1
RPHS2
RPHS1
RPHS2
CSCOMP
CSCOMP
RAMPIN+
RAMPIN-
PWMRMP
RAMPIN+
RAMPIN-
PWMRMP
SCOMP
ISHARE
DACIN
SCOMP
ISHARE
DACIN
BIASIN
EAIN
BIASIN
EAIN
SHARE
ADJUST
ERROR
AMPLIFIER
SHARE
ADJUST
ERROR
AMPLIFIER
+
-
+
-
SYSTEM
REFERENCE
VOLTAGE
SYSTEM
REFERENCE
VOLTAGE
10K
10K
CLOCK
PULSE
GENERATOR
CLOCK
PULSE
GENERATOR
+
-
+
-
20mV
20mV
RAMP
DISCHARGE
CLAMP
RAMP
DISCHARGE
CLAMP
PWM
COMPARATOR
PWM
COMPARATOR
ENABLE
ENABLE
PHASE IC
PHASE IC
-
+
-
+
PHS1
+
-
+
-
PWM
LATCH
DOMINANT
PWM
LATCH
DOMINANT
S
RESET
R
BODY
BRAKING
COMPARATOR
S
RESET
R
BODY
BRAKING
COMPARATOR
CURRENT
SENSE
AMPLIFIER
X34
CURRENT
SENSE
AMPLIFIER
X34
and R
+
-
+
-
X
0.91
X
0.91
PHS2
CSIN-
CSIN-
GATEH
GATEL
CSIN+
GATEH
GATEL
CSIN+
connected between the
CCS
CCS
RCS
RCS
10/01
IR3081
/04
COUT
VIN
VOSNS+
VOUT
GND
VOSNS-