IRF IR3081MTR

IR3081
DATA SHEET
XPHASETM VR 10.0 CONTROL IC
DESCRIPTION
The IR3081 Control IC combined with an IR XPhaseTM Phase IC provides a full featured and flexible way
to implement a complete VR 10.0 power solution. The “Control” IC provides overall system control and
interfaces with any number of “Phase ICs” which each drive and monitor a single phase of a multiphase
converter. The XPhaseTM architecture results in a power supply that is smaller, less expensive, and easier
to design while providing higher efficiency than conventional approaches.
The IR3081 is intended for VRD or VRM/EVRD 10.0 applications that use external VCCVID/VTT circuits.
FEATURES
•
•
•
•
•
•
•
•
•
•
•
•
•
6 bit VR 10.0 compatible VID with 0.5% overall system accuracy
Programmable Dynamic VID Slew Rate
No Discharge of output capacitors during Dynamic VID step-down (can be disabled)
+/-300mV Differential Remote Sense
Programmable 150kHz to 1MHz oscillator
Programmable VID Offset and Load Line output impedance
Programmable Softstart
Programmable Hiccup Over-Current Protection with Delay to prevent false triggering
Simplified Powergood provides indication of proper operation and avoids false triggering
Operates from 12V input with 9.1V Under-Voltage Lockout
6.8V/5mA Bias Regulator provides System Reference Voltage
Enable Input
Small thermally enhanced 28L MLPQ package
22
23
LGND
24
RMPOUT
SS/DEL
25
27
26
PWRGD
VCC
EAOUT
FB
VDRP
VID3
IIN
21
20
19
18
17
16
VDAC
15
14
ROSC
13
TRM4
OCSET
TRM3
VID4
8
Page 1 of 20
N/C
VID2
TRM1
7
VID1
12
6
IR3081
CONTROL
IC
VID0
VOSNS-
5
BBFB
10
4
VBIAS
VID5
11
3
TRM2
2
OSCDS
9
1
ENABLE
28
PACKAGE PINOUT
9/1/03
IR3081
ORDERING INFORMATION
Device
Order Quantity
IR3081MTR
3000 per Reel
IR3081M
5 per Bag
ABSOLUTE MAXIMUM RATINGS
Operating Junction Temperature……………..150oC
Storage Temperature Range………………….-65oC to 150oC
ESD Rating………………………………………HBM Class 1C JEDEC standard
PIN #
1
2-7
8, 9,
11,12
10
13
14
15
16
PIN NAME
OSCDS
VID0-5
TRM1-4
VMAX
20V
20V
Do Not Connect
VMIN
-0.3V
-0.3V
Do Not Connect
ISOURCE
1mA
10mA
Do Not Connect
ISINK
1mA
10mA
Do Not Connect
VOSNSROSC
VDAC
OCSET
IIN
0.5V
20V
20V
20V
20V
-0.5V
-0.5V
-0.3V
-0.3V
-0.3V
10mA
1mA
1mA
1mA
1mA
10mA
1mA
1mA
1mA
1mA
17
18
19
VDRP
FB
EAOUT
20V
20V
10V
-0.3V
-0.3V
-0.3V
5mA
1mA
10mA
5mA
1mA
20mA
20
BBFB
20V
-0.3V
1mA
1mA
21
VBIAS
20V
-0.3V
1mA
1mA
22
VCC
20V
-0.3V
1mA
50mA
23
LGND
n/a
n/a
50mA
1mA
24
RMPOUT
20V
-0.3V
1mA
1mA
25
SS/DEL
20V
-0.3V
1mA
1mA
26
PWRGD
20V
-0.3V
1mA
20mA
27
N/C
n/a
n/a
n/a
n/a
28
ENABLE
20V
-0.3V
1mA
1mA
Page 2 of 20
9/1/03
IR3081
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over: 9.5V ≤ VCC ≤ 14V, 0 oC ≤ TJ ≤ 100 oC
PARAMETER
VDAC Reference
System Set-Point Accuracy
Source Current
Sink Current
VID Input Threshold
VID Input Bias Current
Regulation Detect Comparator
Input Offset
Regulation Detect to EAOUT
Delay
BBFB to FB Bias Current
Ratio
VID 11111x Blanking Delay
VID Step Down Detect
Blanking Time
VID Down BB Clamp Voltage
VID Down BB Clamp Current
Error Amplifier
Input Offset Voltage
FB Bias Current
DC Gain
Gain-Bandwidth Product
Source Current
Sink Current
Max Voltage
Min Voltage
VDRP Buffer Amplifier
Input Offset Voltage
Input Voltage Range
Bandwidth (-3dB)
Input Voltage Range
Slew Rate
IIN Bias Current
Page 3 of 20
TEST CONDITION
-0.3V ≤ VOSNS- ≤ 0.3V, Connect FB to
EAOUT, Measure V(EAOUT) –
V(VOSNS-) deviation from Table 1.
Applies to all VID codes.
RROSC = 41.9kΩ
RROSC = 41.9kΩ
0V ≤ VID0-5 ≤ VCC
MIN
TYP
MAX
0.5
68
47
500
-5
-5
0.95
Measure Time till PWRGD drives low
Measure from VID inputs to EAOUT
UNIT
%
µA
µA
mV
80
55
600
0
0
92
63
700
5
5
µA
mV
130
200
ns
1.00
1.05
µA/µA
800
1.7
ns
µs
Percent of VDAC voltage
70
3.5
75
6.2
80
12
%
mA
Connect FB to EAOUT, Measure
V(EAOUT) – V(DAC). from Table 1.
Applies to all VID codes and -0.3V ≤
VOSNS- ≤ 0.3V. Note 2
RROSC = 41.9kΩ
Note 1
Note 1
-3
4
8
mV
28
90
4
0.4
0.7
125
30
29.5
100
7
0.6
1.2
250
100
31
105
µA
dB
MHz
mA
mA
mV
mV
-8
0.8
1
0.8
0
VBIAS–VEAOUT (referenced to VBIAS)
Normal operation or Fault mode
V(VDRP) – V(IIN), 0.8V ≤ V(IIN) ≤ 5.5V
Note 1
0
0.8
1.7
375
150
8
5.5
5.5
mV
V
MHz
V
1.5
V/µs
µA
6
10
0.75
9/1/03
IR3081
PARAMETER
Oscillator
Switching Frequency
Peak Voltage (5V typical,
measured as % of VBIAS)
Valley Voltage (1V typical,
measured as % of VBIAS)
VBIAS Regulator
Output Voltage
Current Limit
Soft Start and Delay
SS/DEL to FB Input Offset
Voltage
Charge Current
Discharge Current
Charge/Discharge Current
Ratio
Charge Voltage
Delay Comparator Threshold
Discharge Comparator
Threshold
Over-Current Comparator
Input Offset Voltage
OCSET Bias Current
PWRGD Output
Output Voltage
Leakage Current
Enable Input
Threshold voltage
Bias Current
VCC Under-Voltage Lockout
Start Threshold
Stop Threshold
Hysteresis
General
VCC Supply Current
VOSNS- Current
TEST CONDITION
MIN
TYP
MAX
UNIT
RROSC = 41.9kΩ
RROSC = 41.9kΩ
255
70
300
71
345
74
kHz
%
RROSC = 41.9kΩ
11
14
16
%
0 ≤ I(VBIAS) ≤ 5mA
6.5
6
6.8
15
7.1
30
V
mA
With FB = 0V, adjust V(SS/DEL) until
EAOUT drives high
0.85
1.3
1.5
V
40
4
10
70
6
11.5
100
9
13
µA
µA
µA/µA
Relative to Charge Voltage
3.7
70
150
4.0
90
200
4.2
110
250
V
mV
mV
1V ≤ V(OCSET) ≤ 5V
RROSC = 41.9kΩ
-10
28
0
29.5
10
31
mV
µA
150
0
400
10
mV
0V ≤ V(ENABLE) ≤ VCC
500
-5
600
0
700
5
mV
µA
Start – Stop
8.6
8.4
150
9.1
8.9
200
9.6
9.4
300
V
V
mV
-0.3V ≤ VOSNS- ≤ 0.3V, All VID Codes
8
3.5
11
4.5
14
5.5
mA
mA
I(PWRGD) = 4mA
V(PWRGD) = 5.5V
Note 1: Guaranteed by design, but not tested in production
Note 2: VDAC Output is trimmed to compensate for Error Amp input offsets errors
Page 4 of 20
9/1/03
µA
IR3081
PIN DESCRIPTION
PIN#
1
PIN SYMBOL
OSCDS
2-7
8, 9,
11,12
10
13
VID0-5
TRM1-4
VOSNSROSC
14
VDAC
15
OCSET
16
IIN
17
VDRP
18
FB
19
20
EAOUT
BBFB
21
VBIAS
22
23
24
25
VCC
LGND
RMPOUT
SS/DEL
26
PWRGD
27
28
N/C
ENABLE
Page 5 of 20
PIN DESCRIPTION
Apply a voltage greater than VBIAS to disable the oscillator. Used during factory
testing & trimming. Ground or leave open for normal operation.
Inputs to VID D to A Converter
Used for precision post-package trimming of the VDAC voltage. Do not make any
connection to these pins.
Remote Sense Input. Connect to ground at the Load.
Connect a resistor to VOSNS- to program oscillator frequency and FB, OCSET,
BBFB, and VDAC bias currents
Regulated voltage programmed by the VID inputs. Current Sensing and PWM
operation are referenced to this pin. Connect an external RC network to VOSNS- to
program Dynamic VID slew rate.
Programs the hiccup over-current threshold through an external resistor tied to
VDAC and an internal current source. Over-current protection can be disabled by
connecting this pin to a DC voltage no greater than 6.5V (do not float this pin as
improper operation will occur).
Current Sense input from the Phase IC(s). To ensure proper operation bias to at
least 250mV (don’t float this pin).
Buffered IIN signal. Connect an external RC network to FB to program converter
output impedance
Inverting input to the Error Amplifier. Converter output voltage is offset from the
VDAC voltage through an external resistor connected to the converter output voltage
at the load and an internal current source.
Output of the Error Amplifier
Input to the Regulation Detect Comparator. Connect to converter output voltage and
VDRP pin through resistor network to program recovery from VID step-down.
Connect to ground to disable Body BrakingTM during transition to a lower VID code.
6.8V/5mA Regulated output used as a system reference voltage for internal circuitry
and the Phase ICs.
Power for internal circuitry
Local Ground and IC substrate connection
Oscillator Output voltage. Used by Phase ICs to program Phase Delay
Controls Converter Softstart, Power Good, and Over-Current Timing. Connect an
external capacitor to LGND to program the timing. An optional resistor can be added
in series with the capacitor to program the over-current delay time.
Open Collector output that drives low during Softstart and any external fault
condition. Connect external pull-up.
No internal connection
Enable Input. A logic low applied to this pin puts the IC into Fault mode.
9/1/03
IR3081
SYSTEM THEORY OF OPERATION
XPhaseTM Architecture
The XPhaseTM architecture is designed for multiphase interleaved buck converters which are used in applications
requiring small size, design flexibility, low voltage, high current and fast transient response. The architecture can be
used in any multiphase converter ranging from 1 to 16 or more phases where flexibility facilitates the design tradeoff of multiphase converters. The scalable architecture can be applied to other applications which require high
current or multiple output voltages.
As shown in Figure 1, the XPhaseTM architecture consists of a Control IC and a scalable array of phase converters
each using a single Phase IC. The Control IC communicates with the Phase ICs through a 5-wire analog bus, i.e.
bias voltage, phase timing, average current, error amplifier output, and VID voltage. The Control IC incorporates all
the system functions, i.e. VID, PWM ramp oscillator, error amplifier, bias voltage, and fault protections etc. The
Phase IC implements the functions required by the converter of each phase, i.e. the gate drivers, PWM comparator
and latch, over-voltage protection, and current sensing and sharing.
There is no unused or redundant silicon with the XPhaseTM architecture compared to others such as a 4 phase
controller that can be configured for 2, 3, or 4 phase operation. PCB Layout is easier since the 5 wire bus
eliminates the need for point-to-point wiring between the Control IC and each Phase. The critical gate drive and
current sense connections are short and local to the Phase ICs. This improves the PCB layout by lowering the
parasitic inductance of the gate drive circuits and reducing the noise of the current sense signal.
POWER GOOD
PHASE FAULT
VR HOT
12V
ENABLE
VID5
VID0
VID1
IRU3081
CONTROL
IC
PHASE FAULT
CIN
>> BIAS VOLTAGE
VOUT SENSE+
>> PHASE TIMING
VID2
<< CURRENT SENSE
VID3
>> PWM CONTROL
VID4
>> VID VOLTAGE
CURRENT SHARE
IRU3086
PHASE
IC
VOUT+
0.1uF
COUT
VOUT-
PHASE HOT
CCS
RCS
VOUT SENSE-
PHASE FAULT
CURRENT SHARE
IRU3086
PHASE
IC
0.1uF
PHASE HOT
CCS
CONTROL BUS
Page 6 of 20
RCS
ADDITIONAL PHASES
INPUT/OUTPUT
9/1/03
IR3081
Figure 1 – System Block Diagram
PWM Control Method
The PWM block diagram of the XPhaseTM architecture is shown in Figure 2. Feed-forward voltage mode control 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. 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 drops in the PCB related to changes in load current.
VIN
CONTROL IC
PHASE IC
SYSTEM
REFERENCE
VOLTAGE
BIASIN
RAMP GENERATOR
RMPOUT
RAMPIN+
-
VVALLEY
RRAMP1
PWM
LATCH
CLOCK
PULSE
GENERATOR
RAMPIN-
PWM
COMPARATOR
-
VBIAS
PWMRMP
RPWMRMP
X
0.91
+
-
+
+
-
ISHARE
CURRENT
SENSE
AMP
20mV
10K
-
X34
RDRP
VDRP
AMP
VOSNS-
-
+
IROSC
GND
O% DUTY
CYCLE
COMPARATOR
-
+
RVFB
FB
IFB
SHARE
ADJUST
ERROR
AMP
CSCOMP
ERROR
AMP
RAMP
DISCHARGE
CLAMP
SCOMP
CPWMRMP
EAOUT
RAMP
SLOPE
ADJUST
CSIN+
+
VOSNSVDAC
GATEL
+
ENABLE
-
-
EAIN
VOUT
COUT
RRAMP2
VDAC
VBIAS
REGULATOR
VOSNS+
RESET
DOMINANT
R
+
+
GATEH
S
-
VPEAK
+
50%
DUTY
CYCLE
CCS
RCS
CCS
RCS
CSIN-
DACIN
VDRP
+
-
IIN
PHASE IC
SYSTEM
REFERENCE
VOLTAGE
BIASIN
RAMPIN+
+
RRAMP1
PWM
LATCH
CLOCK
PULSE
GENERATOR
RAMPIN-
GATEH
S
PWM
COMPARATOR
-
EAIN
RESET
DOMINANT
R
GATEL
+
RRAMP2
20mV
-
CURRENT
SENSE
AMP
X34
-
+
+
ISHARE
10K
X
0.91
-
SHARE
ADJUST
ERROR
AMP
CSIN+
+
SCOMP
CSCOMP
O% DUTY
CYCLE
COMPARATOR
-
RAMP
DISCHARGE
CLAMP
+
CPWMRMP
RAMP
SLOPE
ADJUST
-
RPWMRMP
ENABLE
+
PWMRMP
CSIN-
DACIN
Figure 2 – PWM Block Diagram
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. 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 RRAMP1 and RRAMP2 connected between the VBIAS
reference voltage and the Phase IC LGND pin. A comparator in the Phase ICs detects the crossing of the oscillator
waveform with 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
synchronization by swapping the RAMP + and – pins.
Page 7 of 20
9/1/03
IR3081
50% RAMP
DUTY CYCLE
RAMP (FROM
CONTROL IC)
SLOPE = 80mV / % DC
VPEAK (5.0V)
VPHASE4&5 (4.5V)
SLOPE = 1.6mV / ns @ 200kHz
SLOPE = 8.0mV / ns @ 1MHz
VPHASE3&6 (3.5V)
VPHASE2&7 (2.5V)
VPHASE1&8 (1.5V)
VVALLEY (1.00V)
CLK1
PHASE IC CLOCK PULSES
CLK2
CLK3
CLK4
CLK5
CLK6
CLK7
CLK8
Figure 3 – 8 Phase Oscillator Waveforms
PWM Operation
The PWM comparator is located in the Phase IC. Upon receiving a clock pulse, the PWM latch is set, the PWMRMP
voltage begins to increase, the low side driver is turned off, and the high side driver is then turned on. When the
PWMRMP voltage exceeds the Error Amp’s output voltage the PWM latch is reset. This turns off the high side
driver, turns on the low side driver, and activates the Ramp Discharge Clamp. The clamp quickly discharges the
PWMRMP capacitor to the VDAC voltage of the Control IC until the next clock pulse.
The PWM latch is reset dominant allowing all phases to go to zero duty cycle within a few tens of nanoseconds in
response to a load step decrease. Phases can overlap and go to 100% duty cycle in response to a load step
increase with turn-on gated by the clock pulses. An Error Amp output voltage greater than the common mode input
range of the PWM comparator results in 100% duty cycle regardless of the voltage of the PWM ramp. This
arrangement guarantees the Error Amp is always in control and can demand 0 to 100% duty cycle as required. It
also favors response to a load step decrease which is appropriate given the low output to input voltage ratio of most
systems. The inductor current will increase much more rapidly than decrease in response to load transients.
Page 8 of 20
9/1/03
IR3081
This control method is designed to provide “single cycle transient response” where the inductor current changes in
response to load transients within a single switching cycle maximizing the effectiveness of the power train and
minimizing the output capacitor requirements. An additional advantage is that differences in ground or input voltage
at the phases have no effect on operation since the PWM ramps are referenced to VDAC.
Body BrakingTM
In a conventional synchronous buck converter, the minimum time required to reduce the current in the inductor in
response to a load step decrease is;
TSLEW = [L x (IMAX - IMIN)] / Vout
The slew rate of the inductor current can be significantly increased by turning off the synchronous rectifier in
response
to a load step decrease. The switch node voltage is then forced to decrease until conduction of the synchronous
rectifier’s body diode occurs. This increases the voltage across the inductor from Vout to Vout + VBODY DIODE. The
minimum time required to reduce the current in the inductor in response to a load transient decrease is now;
TSLEW = [L x (IMAX - IMIN)] / (Vout + VBODY DIODE)
Since the voltage drop in the body diode is often higher than output voltage, the inductor current slew rate can be
increased by 2X or more. This patent pending technique is referred to as “body braking” and is accomplished
through the “0% Duty Cycle Comparator” located in the Phase IC. If the Error Amp’s output voltage drops below
91% of the VDAC voltage this comparator turns off the low side gate driver.
Figure 4 depicts PWM operating waveforms under various conditions
PHASE IC
CLOCK
PULSE
EAIN
PWMRMP
VDAC
91% VDAC
GATEH
GATEL
STEADY-STATE
OPERATION
DUTY CYCLE INCREASE
DUE TO LOAD
INCREASE
DUTY CYCLE DECREASE
DUE TO VIN INCREASE
(FEED-FORWARD)
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
(VCC UV, VCCVID UV, OCP, VID=11111X)
STEADY-STATE
OPERATION
Figure 4 – PWM Operating Waveforms
Lossless Average Inductor Current Sensing
Inductor current can be sensed by connecting a series resistor and a capacitor network in parallel with the inductor
and measuring the voltage across the capacitor. The equation of the sensing network is,
vC ( s ) = v L ( s )
Page 9 of 20
R + sL
1
= iL (s) L
1 + sRS C S
1 + sRS C S
9/1/03
IR3081
Usually the resistor Rcs and capacitor Ccs are chosen so that the time constant of Rcs and Ccs equals the time
constant of the inductor which is the inductance L over the inductor DCR. If the two time constants match, the
voltage across Ccs is proportional to the current through L, and the sense circuit can be treated as if only a sense
resistor with the value of RL was used. The mismatch of the time constants does not affect the measurement of
inductor DC current, but affects the AC component of the inductor current.
The advantage of sensing the inductor current versus high side or low side sensing is that actual output current
being delivered to the load is obtained rather than peak or sampled information about the switch currents. The
output voltage can be positioned to meet a load line based on real time information. Except for a sense resistor in
series with the inductor, this is the only sense method that can support a single cycle transient response. Other
methods provide no information during either load increase (low side sensing) or load decrease (high side sensing).
An additional problem associated with peak or valley current mode control for voltage positioning is that they suffer
from peak-to-average errors. These errors will show in many ways but one example is the effect of frequency
variation. If the frequency of a particular unit is 10% low, the peak to peak inductor current will be 10% larger and
the output impedance of the converter will drop by about 10%. Variations in inductance, current sense amplifier
bandwidth, PWM prop delay, any added slope compensation, input voltage, and output voltage are all additional
sources of peak-to-average errors.
Current Sense Amplifier
A high speed differential current sense amplifier is located in the Phase IC, as shown in figure 5. Its gain decreases
with increasing temperature and is nominally 34 at 25ºC and 29 at 125ºC (-1470 ppm/ºC). This reduction of gain
tends to compensate the 3850 ppm/ºC increase in inductor DCR. Since in most designs the Phase IC junction is
hotter than the inductor these two effects tend to cancel such that no additional temperature compensation of the
load line is required.
The current sense amplifier can accept positive differential input up to 100mV and negative up to -20mV before
clipping. The output of the current sense amplifier is summed with the DAC voltage and sent to the Control IC and
other Phases through an on-chip 10KΩ resistor connected to the ISHARE pin. The ISHARE pins of all the phases
are tied together and the voltage on the share bus represents the total current through all the inductors and is used
by the Control IC for voltage positioning and current limit protection.
vL
iL
CSA
L
RL
Rs
Cs
Vo
Co
vc
CO
Figure 5 – Inductor Current Sensing and Current Sense Amplifier
Average Current Share Loop
Current sharing between phases of the converter is achieved by the average current share loop in each Phase IC.
The output of the current sense amplifier is compared with the share bus less a 20mV offset. If current in a phase is
smaller than the average current, the share adjust amplifier of the phase will activate a current source that reduces
the slope of its PWM ramp thereby increasing its duty cycle and output current. The crossover frequency of the
current share loop can be programmed with a capacitor at the SCOMP pin so that the share loop does not interact
with the output voltage loop.
Page 10 of 20
9/1/03
IR3081
IR3081 THEORY OF OPERATION
Block Diagram
The Block diagram of the IR3081 is shown in figure 6 and discussed in the following section.
+
DISCHARGE
COMPARATOR
R
-
START
STOP
+
+
ENABLE
ENABLE
COMPARATOR
SET
DOMINANT
0.2V
-
-
8.9V
-
+
IDISCHG
-
+
90mV
+
VCHG
4V
ON
OFF
-
VID3
IOCSETIROSC
VID = 11111X
VID4
VDAC
+
+
-
-
0.6V
1.2V
VBIAS
REGULATOR
+
VBIAS
LGND
+
-
VBIAS
5.0V
1.0V
6.8V
-
IROSC
CURRENT
SOURCE
GENERATOR
ROSC
BUFFER
AMP
-
RAMP GENERATOR
+
RMPOUT
FB
IROSC IFB
VID DAC OUTPUT
VOSNS-
50%
DUTY
CYCLE
EAOUT
ERROR
AMP
VID STEP-DOWN
IROSC
IROSC
IROSC
IROSC
BBFB
SOFTSTART
CLAMP
+
IROSC
VID
CONTROL
IROSC
VID2
1.3V
+
VID1
OCSET
DISABLE
SS/DEL
IROSC
IROSC
IROSC
VDRP
VDRP
AMP
IIN
SS/DEL
DISCHARGE
66uA
VID0
OC
COMPARATOR
DELAY
COMPARATOR
-
ICHG
+
OVER
CURRENT
-
6uA
VID5
PWRGD
S
+
+
9.1V
UVLO
COMPARATOR
-
+
FAULT
LATCH
START
STOP
+
VCC
+
VCC
ROSC
Figure 6 – IR3081 Block Diagram
VID Control
A 6-bit VID voltage compatible with VR 10.0, as shown in Table 1 is available at the VDAC pin. A detailed block
diagram of the VID control circuitry can be found in Figure 7. The VID pins are require an external bias voltage and
should not be floated. The VID input comparators, with 0.6V reference, monitor the VID pins and control the 6 bit
Digital-to-Analog Converter (DAC) whose output is sent to the VDAC buffer amplifier. The output of the buffer amp
is the VDAC pin. The VDAC voltage is post-package trimmed to compensate for the input offsets of the Error Amp
to provide a 1.0% system accuracy. The actual VDAC voltage does not determine the system accuracy and has a
wider tolerance.
Page 11 of 20
9/1/03
IR3081
The IR3081 can accept changes in the VID code while operating and vary the DAC voltage accordingly. The
sink/source capability of the VDAC buffer amp is programmed by the same external resistor that sets the oscillator
frequency. The slew rate of the voltage at the VDAC pin can be adjusted by an external capacitor between VDAC
pin and the VOSNS- pin. A resistor connected in series with this capacitor is required to compensate the VDAC
buffer amplifier. Digital VID transitions result in a smooth analog transition of the VDAC voltage and converter
output voltage minimizing inrush currents in the input and output capacitors and overshoot of the output voltage.
It is desirable to prevent negative inductor currents in response to a request for a lower VID code. Negative current
transforms the buck converter into a boost converter and transfers energy from the output capacitors back into the
input voltage. This energy can cause voltage spikes and damage the silver box or other components unless they
are specifically designed to handle it. Furthermore, power is wasted during the transfer of energy from the output
back to the input.
The IR3081 includes circuitry that turns off both control and synchronous MOSFETs in response to a lower VID
code so that the load current discharges the output capacitors instead of the inductors. A lower VID code is
detected by the VID step-down detect comparator which monitors the “fast” output of the DAC (plus 7mV for noise
immunity) compared to the “slow” output of the VDAC pin. If a dynamic VID step down is detected, the body brake
latch is set and the output of the error amplifier is pulled down to 75% of the DAC voltage by the VID body brake
clamp. This triggers the Body BrakingTM function in the phase ICs causing them to turn off both their drivers.
The converter’s output voltage needs to be monitored and compared to the VDAC voltage to determine when to
resume normal operation. Unfortunately, the voltage on the FB pin can be pulled down by its compensation network
during the sudden decrease in the Error Amp’s output voltage so an additional pin BBFB is provided. The BBFB pin
is connected to the converter output voltage and VDRP pin with resistors of the same value as on the FB pin and
therefore provides an un-corrupted representation of converter output voltage. The regulation detect comparator
compares the BBFB to the VDAC voltage and resets the body brake latch releasing the error amp’s output and
allowing normal operation to resume. Body BrakingTM during a transition to a lower VID code can be disabled by
connecting the BBFB pin to ground.
Page 12 of 20
9/1/03
IR3081
800ns
BLANKING
VID5
VID0
DIGITAL TO
ANALOG
CONVERTER
VID INPUT
COMPARATORS
(1 OF 6
SHOWN)
VID1
VID2
VID3
+
VDAC BUFFER
AMP
"FAST" VDAC
+
ISOURCE
VID4
+
+
VID = 11111X DETECT
-
"SLOW" VDAC
VDAC
ISINK
-
-
0.6V
VOSNS-
-
EAOUT
7mV
VID DOWN
BB CLAMP
+
+
75%
-
ENABLE
RESET
DOMINANT
S
VID STEP-DOWN
DETECT
COMPARATOR
+
IBBFB
+
BODY
BRAKE
LATCH
1.7us
BLANKING
R
REGULATION
DETECT
COMPARATOR
BBFB
-
TO ERROR AMP
IROSC (From Current Source Generator)
Figure 7– VID Control Block Diagram
Page 13 of 20
9/1/03
IR3081
Processor Pins (0 = low, 1 = high)
VID4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
VID3
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
VID2
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
VID1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
VID0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
VID5
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Vout
(V)
0.8375
0.8500
0.8625
0.8750
0.8875
0.9000
0.9125
0.9250
0.9375
0.9500
0.9625
0.9750
0.9875
1.0000
1.0125
1.0250
1.0375
1.0500
1.0625
1.0750
1.0875
OFF4
OFF4
1.1000
1.1125
1.1250
1.1375
1.1500
1.1625
1.1750
1.1875
1.2000
Processor Pins (0 = low, 1 = high)
VID4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
VID3
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
VID2
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
VID1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
VID0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
VID5
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Vout
(V)
1.2125
1.2250
1.2375
1.2500
1.2625
1.2750
1.2875
1.3000
1.3125
1.3250
1.3375
1.3500
1.3625
1.3750
1.3875
1.4000
1.4125
1.4250
1.4375
1.4500
1.4625
1.4750
1.4875
1.5000
1.5125
1.5250
1.5375
1.5500
1.5625
1.5750
1.5875
1.6000
Note: 3. Output disabled (Fault mode)
Table 1 - Voltage Identification (VID)
Adaptive Voltage Positioning
Adaptive voltage positioning is needed to reduce the output voltage deviations during load transients and the power
dissipation of the load when it is drawing maximum current. The circuitry related to voltage positioning is shown in
Figure 8. Resistor RFB is connected between the Error Amp’s inverting input pin FB and the converter’s output
voltage. An internal current source whose value is programmed by the same external resistor that programs the
oscillator frequency pumps current into the FB pin. The error amp forces the converter’s output voltage lower to
maintain a balance at its inputs. RFB is selected to program the desired amount of fixed offset voltage below the
DAC voltage.
The voltage at the VDRP pin is a buffered version of the share bus and represents the sum of the DAC voltage and
the average inductor current of all the phases. The VDRP pin is connected to the FB pin through the resistor RDRP.
Since the Error Amp will force the loop to maintain FB to be equal to the VDAC reference voltage, a current will be
flow into the FB pin equal to (VDRP-VDAC) / RDRP. When the load current increases, the adaptive positioning
voltage increases accordingly. More current flows through the feedback resistor RFB, and makes the output voltage
lower proportional to the load current. The positioning voltage can be programmed by the resistor RDRP so that the
droop impedance produces the desired converter output impedance. The offset and slope of the converter output
impedance are referenced to and therefore independent of the VDAC voltage.
Page 14 of 20
9/1/03
IR3081
ISHARE
Vo
-
Rf b
Droop
Amplifier
-
Rv drp
VDRP
Phase IC
IIN
Current Sense
Amplifier
ISHARE
+
VDAC
CS-
... ...
If b
VDAC
CS+
VDAC
10k
CS+
-
+
FB
10k
+
EA
-
VDAC
Current Sense
Amplifier
Phase IC
Error
Amplifier
+
Control IC
CS-
Figure 8 - Adaptive voltage positioning
Inductor DCR Temperature Correction
If the thermal compensation of the inductor DCR provided by the temperature dependent gain of the current sense
amplifier is not adequate, a negative temperature coefficient (NTC) thermistor can be used for additional correction.
The thermistor should be placed close to the inductor and connected in parallel with the feedback resistor, as
shown in Figure 9. The resistor in series with the thermistor is used to reduce the nonlinearity of the thermistor. A
similar network must be placed on the BBFB to ensure proper operation during a transition to a lower VID code with
Body BrakingTM.
Control IC
VDAC
Error
Amplifier
EA
Rf b
+
-
FB
If b
Rf b
Rt
Rv drp
Droop
Amplifier
-
Vo
VDRP
IIN
+
Figure 9 - Temperature compensation of inductor DCR
Remote Voltage Sensing
To compensate for impedance in the ground plane, the VOSNS- pin is used for remote sensing and connects
directly to the load. The VDAC voltage is referenced to VOSNS- to avoid additional error terms or delay related to a
separate differential amplifier. The capacitor connecting the VDAC and VOSNS- pins ensure that high speed
transients are fed directly into the error amp without delay.
Soft Start, Over-Current Fault Delay, and Hiccup Mode
Page 15 of 20
9/1/03
IR3081
The IR3081 has a programmable soft-start function to limit the surge current during the converter start-up. A
capacitor connected between the SS/DEL and LGND pins controls soft start as well as over-current protection delay
and hiccup mode timing. A charge current of 66uA and discharge current of 6uA control the up slope and down
slope of the voltage at the SS/DEL pin respectively
Figure 11 depicts the various operating modes as controlled by the SS/DEL function. If there is no fault, the SS/DEL
pin will begin to be charged. The error amplifier output is clamped low until SS/DEL reaches 1.3V. The error
amplifier will then regulate the converter’s output voltage to match the SS/DEL voltage less the 1.3V offset until it
reaches the level determined by the VID inputs. The SS/DEL voltage continues to increase until it rises above 3.91V
and allows the PWRGD signal to be asserted. SS/DEL finally settles at 4V, indicating the end of the soft start.
Under Voltage Lock Out and VID=11111x faults as well as a low signal on the ENABLE input immediately sets the
fault latch causing SS/DEL to begin to discharge. The SS/DEL capacitor will continue to discharge down to 0.2V. If
the fault has cleared the fault latch will be reset by the discharge comparator allowing a normal soft start to occur.
A delay is included if an over-current condition occurs after a successful soft start sequence. This is required since
over-current conditions can occur as part of normal operation due to load transients or VID transitions. If an overcurrent fault occurs during normal operation it will initiate the discharge of the capacitor at SS/DEL but will not set
the fault latch immediately. If the over-current condition persists long enough for the SS/DEL capacitor to discharge
below the 90mV offset of the delay comparator, the Fault latch will be set pulling the error amp’s output low
inhibiting switching in the phase ICs and de-asserting the PWRGD signal. The delay can be reduced by adding a
resistor in series with the delay capacitor. The delay comparator’s offset voltage is reduced by the drop in the
resistor caused by the discharge current. To prevent the charge current from creating an offset exceeding the
SS/DEL to FB input offset voltage the value of the resistor should be 10KΩ or less to avoid interference with the soft
start function.
The SS/DEL capacitor will continue to discharge until it reaches 0.2V and the fault latch is reset allowing a normal
soft start to occur. If an over-current condition is again encountered during the soft start cycle the fault latch will be
set without any delay and hiccup mode will begin. During hiccup mode the 11 to 1 charge to discharge ratio results
in a 9% hiccup mode duty cycle regardless of at what point the over-current condition occurs.
If SS/DEL pin is pulled below 0.9V, the converter can be disabled.
Under Voltage Lockout (UVLO)
The UVLO function monitors the IR3081’s VCC supply pin and ensures that IR3081 has a high enough voltage to
power the internal circuit. The IR3081’s UVLO is set higher than the minimum operating voltage of compatible
Phase ICs thus providing UVLO protection for them as well. During power-up the fault latch is reset when VCC
exceeds 9.1V and there is no other fault. If the VCC voltage drops below 8.9V the fault latch will be set. For
converters using a separate 5V supply for gate driver bias an external UVLO circuit can be added to prevent
operation until adequate voltage is present. A diode connected between the 5V supply and the SS/DEL pin provides
a simple 5V UVLO function.
Over Current Protection (OCP)
The current limit threshold is set by a resistor connected between the OCSET and VDAC pins. If the IIN pin voltage,
which is proportional to the average current plus DAC voltage, exceeds the OCSET voltage, the over-current
protection is triggered.
VID = 11111X Fault
VID codes of 111111 and 111110 will set the fault latch and disable the error amplifier. An 800ns delay is provided
to prevent a fault condition from occurring during Dynamic VID changes.
Page 16 of 20
9/1/03
IR3081
8.9V
UVLO
VCC
(12V)
ENABLE
3.91V
SS/DEL
1.3V
VOUT
PWRGD
OCP THRESHOLD
IOUT
START-UP
(ENABLE GATES
FAULT MODE)
NORMAL OPERATION
(VOUT CHANGES DUE TO LOAD
AND VID CHANGES)
OCP
DELAY
HICCUP OVER-CURRENT
PROTECTION
RE-START
AFTER
OCP
POWER-DOWN
(VCC GATES
FAULT MODE)
Figure 11 – Operating Waveforms
Power Good Output
The PWRGD pin is an open-collector output and should be pulled up to a voltage source through a resistor. During
soft start, the PWRGD remains low until the output voltage is in regulation and SS/DEL is above 3.91V. The
PWRGD pin becomes low if the fault latch is set. A high level at the PWRGD pin indicates that the converter is in
operation and has no fault, but does not ensure the output voltage is within the specification. Output voltage
regulation within the design limits can logically be assured however, assuming no component failure in the system.
Load Current Indicator Output
The IIN pin voltage represents the average current of the converter plus the DAC voltage. The load current can be
retrieved by subtracting the VDAC voltage from the IIN voltage.
System Reference Voltage (VBIAS)
The IR3081 supplies a 6.8V/5mA precision reference voltage from the VBIAS pin. The oscillator ramp trip points are
based on the VBIAS voltage so it should be used to program the Phase ICs phase delay to minimize phase errors.
Enable Input
Pulling the ENABLE pin below 0.6V sets the Fault Latch.
Page 17 of 20
9/1/03
IR3081
APPLICATIONS INFORMATION
POWERGOOD
VRHOT
PHASE FAULT
12V
RCS-
10
16
CSIN+
20
18
19
17
CSIN-
DACIN
BIASIN
VOUT+
DISTRIBUTION
IMPEDANCE
11
VCC
LGND
PWMRMP
EAIN
13
12
COUT
VOUT10
6
SCOMP
RPHASE2
RPHASE3
VOUT SENSE+
15
14
0.1uF
10
VOUT SENSE-
RPWMRMP
0.1uF
RVDRP
RCS-
16
15
16
0.1uF
CSIN+
19
18
17
CSIN-
IR3086
PHASE
IC
HOTSET
VRHOT
ISHARE
SCOMP
6
CSCOMP
GATEH
PGND
GATEL
VCCL
15
14
13
12
11
VCC
RMPIN-
RPHASE2
RPHASE3
RCS+
VCCH
10
4
RSHARE
5
CVDAC
DACIN
20
3
RVDAC
PHSFLT
BIASIN
2
RMPIN+
LGND
1
PWMRMP
RVDRP
CCS+
CCS-
RBIASIN
VDAC
TRM4
ROSC
PGND
GATEL
17
ROCSET
ROSC
GATEH
18
14
8
OCSET
13
VID4
19
CSCOMP
EAIN
IIN
0.1uF
VCCL
9
FB
VDRP
ISHARE
7
EAOUT
VID3
VRHOT
CIN
RCS+
VCCH
IR3086
PHASE
IC
HOTSET
CPWMRMP 8
VID2
21
20
RMPIN+
RMPIN-
RPHASE1
23
22
27
24
26
28
VID1
RVFB
VCC
LGND
RMPOUT
N/C
PWRGD
ENABLE
IR3081
CONTROL
IC
VID0
TRM3
7
VOSNS-
6
VID4
TRM2
5
VID3
VBIAS
BBFB
TRM1
4
VID2
RVFB
VID5
9
3
VID1
5
0.1uF
12
VID0
OSCDS
10
2
11
1
VID5
SS/DEL
ENABLE
25
CSS/DEL
4
9
3
7
RSS/DEL
2
CPWMRMP 8
1
PHSFLT
RPHASE1
0.1uF
CCS+
CCS-
RBIASIN
0.1uF
10
RPWMRMP
0.1uF
RCS-
CCS+
CCS19
18
20
16
CSIN+
CSIN-
DACIN
BIASIN
0.1uF
CSCOMP
GATEH
PGND
GATEL
15
14
13
12
11
10
VCC
VCCL
LGND
SCOMP
6
RPHASE3
EAIN
ISHARE
9
HOTSET
VRHOT
PWMRMP
IR3086
PHASE
IC
RMPIN-
RPHASE2
5
RCS+
VCCH
7
4
RMPIN+
CPWMRMP 8
3
PHSFLT
RPHASE1
1
2
17
RBIASIN
0.1uF
10
RPWMRMP
0.1uF
RCS-
16
0.1uF
CSIN+
19
18
20
17
CSIN-
DACIN
BIASIN
CSCOMP
GATEH
PGND
GATEL
15
14
13
12
11
VCC
VCCL
10
SCOMP
6
RPHASE3
EAIN
ISHARE
LGND
VRHOT
PWMRMP
HOTSET
RPHASE2
5
IR3086
PHASE
IC
RMPIN-
9
4
RCS+
VCCH
7
3
RMPIN+
CPWMRMP 8
2
PHSFLT
RPHASE1
1
CCS+
CCS-
RBIASIN
0.1uF
10
RPWMRMP
0.1uF
RCS-
16
0.1uF
CSIN+
19
18
20
17
CSIN-
DACIN
BIASIN
GATEH
PGND
GATEL
15
14
13
12
11
VCC
VCCL
10
SCOMP
6
RPHASE3
CSCOMP
EAIN
ISHARE
LGND
VRHOT
9
HOTSET
PWMRMP
IR3086
PHASE
IC
RMPIN-
RPHASE2
5
RCS+
VCCH
7
3
4
RMPIN+
CPWMRMP 8
2
PHSFLT
RPHASE1
1
CCS+
CCS-
RBIASIN
0.1uF
10
RPWMRMP
0.1uF
Figure 8 – IR3081/3086 5 Phase VRM/EVRD 10.0 Converter
LAYOUT GUIDELINES
The following layout guidelines are recommended to reduce the parasitic inductance and resistance of the
PCB layout, therefore minimizing the noise coupled to the IC.
•
Dedicate at least one middle layer for a ground plane, which is then split into signal ground plane
(LGND) and power ground plane (PGND).
•
Connect the ground tab under the control IC to LGND plane through vias. Place the resistor ROSC as
close as possible to ROSC pin of the control IC, and place the over-current limit resistor ROCSET as
close as possible to OCSET and VDAC pins of the control IC.
•
Bus signals should not cross over the fast transition nodes, such as switching nodes and gate drive
output.
•
Use Kelvin connections for the current sense signals, and use the ground plane to shield the current
sense traces.
•
Use Kelvin connections for the remote voltage sense signals, and avoid crossing over the fast transition
nodes.
Page 18 of 20
9/1/03
IR3081
PERFORMANCE CHARACTERISTICS
Oscillator Frequency (kHz)
Figure 13 - Oscillator Frequency versus ROSC
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
90
95
100
ROSC (K Ohms)
Figure 14 - IFB, BBFB, & OCSET Bias Currents vs ROSC
125
115
105
95
85
uA
75
65
55
45
35
25
15
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
ROSC (K Ohm)
Figure 15 - VDAC Source & Sink Currents vc ROSC (includes OCSET
Bias Current)
325
300
275
250
225
uA
200
175
ISINK
150
ISOURCE
125
100
75
50
25
0
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
ROSC (K ohm)
Figure 16 - Bias Current Accuracy versus ROsC (includes
temperature and input voltage variation)
14%
+/-3 Sigma Variation (%)
12%
10%
FB, BBFB, OCSET Bias
Current
8%
VDAC Sink Current
6%
VDAC Source Current
4%
2%
0%
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
ROSC (K Ohm)
Page 19 of 20
9/1/03
IR3081
PACKAGE INFORMATION
28L MLPQ (5 x 5 mm Body) – θJA = 30oC/W, θJC = 3oC/W
5.40 – 6.00
5.00
3.90
3.15
Holes:
Φ0.3-0.33
1.20
3.15 3.90
5.00
5.40 - 6.00
0.23
0.50
0.75-1.05
Note: All dimensions are in Millimeters.
Data and specifications subject to change without notice.
This product has been designed and qualified for the Consumer market.
Qualification Standards can be found on IR’s Web site.
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105
TAC Fax: (310) 252-7903
Visit us at www.irf.com for sales contact information.
www.irf.com
Page 20 of 20
9/1/03