NCP6251
Product Preview
2/3/4-Phase Controller for
CPU Applications
The NCP6251 is a multiphase synchronous buck regulator
controller designed to power the Core and Northbridge of an AMD
microprocessor. The controller has a user configurable two, three, or
four phase regulator for the Core and an independent single phase
regulator to power the microprocessor Northbridge. The NCP6251
incorporates differential voltage sensing, differential phase current
sensing, optional load−line voltage positioning, and programmable
VDD and VDDNB offsets to provide accurately regulated power
parallel− and serial−VID AMD processors. Dual−edge multiphase
modulation provides the fastest initial response to dynamic load
events. This reduces system cost by requiring less bulk and ceramic
output capacitance to meet transient regulation specifications.
High performance operational error amplifiers are provided to
simplify compensation of the VDD and VDDNB regulators. Dynamic
Reference Injection further simplifies loop compensation by
eliminating the need to compromise between response to load
transients and response to VID code changes.
Features
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Meets AMD’s Hybrid VR Specifications
Up to Four VDD Phases
Single−Phase VDDNB Controller
Dual−Edge PWM for Fastest Initial Response to Transient Loading
High Performance Operational Error Amplifiers
Internal Soft−Start and Slew Rate Limiting
Dynamic Reference Injection (Patent #US07057381)
DAC Range from 12.5 mV to 1.55 V
$0.6% DAC Accuracy from 0.8 V to 1.55 V
VDD and VDD Offset Ranges 0 mV − 800 mV
True Differential Remote Voltage Sense Amplifiers
Phase−to−Phase IDD Current Balancing
Differential Current Sense Amplifiers for Each Phase of Each Output
“Lossless” Inductor Current Sensing for VDD and VDDNB Outputs
Supports Load Lines (Droop) for VDD and VDDNB Outputs
Oscillator Range of 100 kHz − 1 MHz
Tracking Overvoltage Protection
Output Inductor DCR−Based Over Current Protection for VDD and
VDDNB Outputs
Guaranteed Startup into Precharged Loads
Temperature Range: 0°C to 70°C
Two Stage Overcurrent Protection
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MARKING
DIAGRAM
1
NCP6251
AWLYYWWG
1 48
QFN48, 7x7
CASE 485AJ
A
WL
YY
WW
G
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
ORDERING INFORMATION
Device
NCP6251MNR2G
Package
Shipping†
QFN48
(Pb−Free)
2500 / Tape & Reel
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications
Brochure, BRD8011/D.
Applications
• Desktop Processors
• Server Processors
• High−End Notebook PCs
This document contains information on a product under development. ON Semiconductor
reserves the right to change or discontinue this product without notice.
© Semiconductor Components Industries, LLC, 2010
October, 2010 − Rev. P0
1
Publication Order Number:
NCP6251/D
G1
G2
G3
G4
NB_G
DRVON
NB_DRVON
PWRGOOD
SVD/VID2
SVC/VID3
ENABLE
PWROK
NCP6251
48
1
VID1
VID0
NB_COMP
NB_FB
NB_DROOP
NB_VS+
NB_VS−
NB_OFFSET
NB_DIFFOUT
ROSC
VID5
VID4
CS1
CS1N
CS2
CS2N
CS3
CS3N
CS4
CS4N
ILIM
VCCB
NB_CS
NB_CSN
VCCA
GND
COMP
FB
DROOP
VS+
VS−
OFFSET
DIFFOUT
VFIX
12VMON
PSI_L
Figure 1. Pinout
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2
NCP6251
NB_VS+
−
+
NB_VS−
Diff Amp
NB_DIFFOUT
NB_FB
+
−
OVP
ILIMIT_NB +
−
Error Amp
ILIMIT_NB =
ILIMIT_VDD/N
(N = VDD
phase count)
NB_DROOP
Gain = 1
Droop Amplifier
1.3 V
+
−
Gain = 6
NB_SRL
NB_DAC
NB_VS+
NB_VS−
NB OFFSET
SCALING
X
NORMAL OPERATION
BOOT_VID & VFIX MODES
+
NB
NB Slew
Rate Limit
VDD Slew
Rate Limit
VDD_SRL OUT
−
+
Diff Amp
PVI/SVI
HYBRID
INTERFACE
VDD_DAC OUT
+
NORMAL OPERATION
BOOT_VID & VFIX MODES
VDD
X
VDD OFFSET
SCALING
+
−
1.3 V
NB_DRVON
NB_OFFSET
NB_DAC OUT
NB_SRL OUT
fNB = 1.27 x fVDD
DIFFOUT
NB REGULATOR
Fault Logic
and
Monitor Circuits
+
NB
Oscillator
VS−
VS+
VDD PSI_L
FAULT
NB_COMP
FB
HI−Z
+
−
1.3 V
NB_CS
NB_CSN
NB_G
PWM_NB
PWRGOOD
PWROK
VID0
VID1
VID2/SVD
VID3/SVC
VID4
VID5
PSI_L
OFFSET
FLAG
Error Amp
COMP
GND
DROOP
Gain = 1
Droop Amplifier
CS1
CS1N
CS2
CS2N
CS3
CS3N
CS4
CS4N
+
−
Gain = 6
+
−
Gain = 6
+
−
Gain = 6
+
−
Gain = 6
1.3 V
VDD PSI_L
+
+
−
PWM1
+
−
PWM2
+
−
PMW3
+
−
+
+
+
+
HI−Z
HI−Z
HI−Z
HI−Z
PWM4
VDD
Oscillator
G1
G2
G3
G4
SHED
OVP
ROSC
ILIMIT_VDD
ILIM
+
−
ENABLE
VCCA
VCCB
+
+
−
5V UVLO
4.25V/4.05V
12VMON
VDD_SRL
VDD_DAC
VS+
VS−
+
−
12V UVLO
8.5V/7.5V
VDD REGULATOR
Fault Logic
3−Phase
Detection
and
Monitor Circuits
NCP5393B
Figure 2. NCP6251 Block Diagram
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3
DRVON
TBD
TBD
NCP6251
Figure 3. NCP6251 Configured for 3 + 1 Phases, with Optional Droop
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4
NCP6251
NCP6251 PIN DESCRIPTIONS
Pin No.
Symbol
1
VCCA
5 V supply pin for the NCP6251. The VCC bypassing capacitance must be connected between this
pin and GND (preferably returned to the package flag).
Description
2
GND
Small−signal power supply return. This pin should be tied directly to the package flag (exposed pad).
3
COMP
Output of the voltage error amplifier for the VDD regulator.
4
FB
Voltage error amplifier inverting input for the VDD regulator.
5
DROOP
6
VS+
Non−inverting input to the differential remote sense amplifier for the VDD regulator.
7
VS−
Inverting input to the differential remote sense amplifier for the VDD regulator.
8
OFFSET
Input for offset voltage to be added to the VDD DAC’s output voltage. Ground this pin for zero VDD
offset.
9
DIFFOUT
Output of the differential remote sense amplifier for the VDD regulator.
10
VFIX
Voltage output signal proportional to total current drawn from the VDD regulator. Used when load line
operation (“droop”) is desired.
When pulled low, this pin causes the levels on the SVC (VID3) and SVD (VID2) pins to be decoded
as a two−bit DAC code, which controls the VDD and VDDNB outputs. Internally pulled high by 5 mA to
VCC
11
12VMON
12
PSI_L
UVLO monitor input for the 12 V power rail.
Determines number of phases operating in PSI_L mode. Phase shed count is locked upon ENABLE
assertion. After soft−start, becomes power saving control in PVID mode. Low = phase shed
operation, High = normal operation.
13
CS1
Non−inverting input to current sense amplifier #1 for the VDD regulator. See Table: “Pin Connections
vs. Phase Count”
14
CS1N
15
CS2
16
CS2N
17
CS3
18
CS3N
19
CS4
20
CS4N
21
ILIM
22
VCCB
5 V supply pin. Tie this pin to VCCA (Pin 1).
23
NB_CS
Non−inverting input to the current sense amplifier for the VDDNB regulator
24
NB_CSN
25
VID4
Parallel Voltage ID DAC Input 4. Not used in SVI mode.
26
VID5
Parallel Voltage ID DAC Input 5. Not used in SVI mode.
27
ROSC
28
NB_DIFFOUT
Output of the differential remote sense amplifier for the VDDNB regulator.
29
NB_OFFSET
Input for offset voltage to be added to the VDDNB DAC’s output voltage. Ground this pin for zero
VDDNB offset.
Inverting input to current sense amplifier #1 for the VDD regulator. See Table: “Pin Connections vs.
Phase Count”
Non−inverting input to current sense amplifier #2 for the VDD regulator. See Table: “Pin Connections
vs. Phase Count”
Inverting input to current sense amplifier #2 for the VDD regulator. See Table: “Pin Connections vs.
Phase Count”
Non−inverting input to current sense amplifier #3 for the VDD regulator. See Table: “Pin Connections
vs. Phase Count”
Inverting input to current sense amplifier #3 for the VDD regulator. See Table: “Pin Connections vs.
Phase Count”
Non−inverting input to current sense amplifier #4 for the VDD regulator. See Table: “Pin Connections
vs. Phase Count”
Inverting input to current sense amplifier #4 for the VDD regulator. See Table: “Pin Connections vs.
Phase Count”
Overcurrent shutdown threshold for VDD and VDDNB. A resistor divider from ROSC to GND is
typically used to develop an appropriate voltage on ILIM. This will set the two-stage over current
protection, ILIM1 and ILIM2. ILIM1 is the first stage OCP with a delayed latch response. ILIM2 is a higher
value, typically 1.3 x ILIM1, it is an immediate latch response.
Inverting input to the current sense amplifier for the VDDNB regulator
A resistance from this pin to ground programs the VDD and VDDNB oscillator frequencies. This pin
supplies a trimmed output voltage of 2 V.
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5
NCP6251
NCP6251 PIN DESCRIPTIONS
Pin No.
Symbol
30
NB_VS−
Inverting input to the differential remote sense amplifier for the VDDNB regulator.
Description
31
NB_VS+
Non−inverting input to the differential remote sense amplifier for the VDDNB regulator.
32
NB_DROOP
33
NB_FB
Voltage error amplifier inverting input for the VDDNB regulator.
34
NB_COMP
Output of the voltage error amplifier for the VDDNB regulator.
35
VID0
Parallel Voltage ID DAC Input 0. Not used in SVI mode.
36
VID1
Parallel Voltage ID DAC Input 1. Also used for PVI or SVI mode selection.
Voltage output signal proportional to total current drawn from the VDDNB regulator. Used when load
line operation (“droop”) is desired.
37
PWROK
System power supplies status input. Used in SVI mode only.
38
ENABLE
High = Run, Low = Standby/Reset.
39
VID3/SVC
Parallel Voltage ID DAC Input 1. Also used in SVI mode.
40
VID2/SVD
Parallel Voltage ID DAC Input 1. Also used in SVI mode.
41
PWRGOOD
Open drain output. High indicates that the active output(s) are within specification. Internally pulled
high by 5 mA to VCC
42
NB_DRVON
Bidirectional Gate Drive Enable to the gate driver for the VDDNB regulator.
43
DRVON
44
NB_G
45
G4
PWM output #4. See Table: “Pin Connections vs. Phase Count”
46
G3
PWM output #3. See Table: “Pin Connections vs. Phase Count”
47
G2
PWM output #2. See Table: “Pin Connections vs. Phase Count”
48
G1
PWM output #1. See Table: “Pin Connections vs. Phase Count”
FLAG
PGND
Bidirectional Gate Drive Enable to gate drivers for the VDD regulator.
PWM output to the VDDNB gate driver.
High−current power supply return via metal pad (flag) underneath package. The package flag should
be tied directly to Pin 2.
PIN CONNECTIONS VS. PHASE COUNT
Number of
Phases
G4
G3
G2
G1
CS4 &
CS4N
CS3 &
CS3N
CS2 &
CS2N
CS1 &
CS1N
4
Phase 4
Out
Phase 3
Out
Phase 2
Out
Phase 1
Out
Phase 4 CS
Input
Phase 3 CS
Input
Phase 2 CS
Input
Phase 1 CS
Input
3
Tie to
GND
Phase 3
Out
Phase 2
Out
Phase 1
Out
Tie to GND
or VDD
Phase 3 CS
Input
Phase 2 CS
Input
Phase 1 CS
Input
2
Tie to
GND
Phase 2
Out
Tie to
GND
Phase 1
Out
Tie to GND
or VDD
Phase 2 CS
input
Tie to GND
or VDD
Phase 1 CS
Input
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NCP6251
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL INFORMATION
Pin Symbol
VMAX
VMIN
ISOURCE
ISINK
12VMON
25 V
−0.3 V
N/A
50 mA
VCC
7.0 V
−0.3 V
N/A
10 mA
COMP, NB_COMP
5.5 V
−0.3 V
10 mA
10 mA
DROOP, NB_DROOP
5.5 V
−0.3 V
5 mA
5 mA
DIFFOUT, NB_DIFFOUT
5.5 V
−0.3 V
20 mA
20 mA
DRVON, NB_DRVON
5.5 V
−0.3 V
5 mA
10 mA
PWRGOOD
5.5 V
−0.3 V
N/A
20 mA
VS+, NB_VS+
3V
−0.3 V
1 mA
1 mA
VS−, NB_VS−
0.3 V
−0.3 V
1 mA
1 mA
ROSC
5.5 V
−0.3 V
1 mA
N/A
All Other Pins
5.5 V
−0.3 V
N/A
N/A
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
NOTE: All signals are referenced to GND unless noted otherwise.
THERMAL INFORMATION
Rating
Symbol
Value
Unit
Thermal Characteristic, QFN Package (Note 1)
RqJA
30.5
°C/W
Operating Junction Temperature Range (Note 2)
TJ
0 to 125
°C
Operating Ambient Temperature Range
TA
0 to 70
°C
Maximum Storage Temperature Range
TSTG
−55 to +150
°C
Moisture Sensitivity Level, QFN Package
MSL
1
* The maximum package power dissipation must be observed.
1. JESD 51−5 (1S2P Direct−Attach Method) with 0 LFM.
2. JESD 51−7 (1S2P Direct−Attach Method) with 0 LFM.
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NCP6251
ELECTRICAL CHARACTERISTICS (Unless otherwise stated: 0°CvTAv70°C; 4.75 VvVCCv5.25 V; All DAC Codes; CVCC = 0.1 mF)
Parameter
Test Conditions
Min
Typ
Max
Unit
−200
−
200
nA
−1.0
−
1.0
mV
ERROR AMPLIFIERS (VDD & VDDNB)
Input Bias Current
Input Offset Voltage (Note 3)
V+ = V− = 1.3V
Open Loop DC Gain
CL = 60 pF to GND, RL = 10 kW to GND
−
80
−
dB
Open Loop Unity Gain Bandwidth
CL = 60 pF to GND, RL = 10 kW to GND
−
15
−
MHz
Open Loop Phase Margin
CL = 60 pF to GND, RL = 10 kW to GND
−
70
−
deg
Slew Rate
DVIN = 100 mV, AV = −10 V/V,
1.5 V < VCOMP < 2.5 V,
CL = 60 pF, DC Loading = $125 mA
−
5
−
Maximum Output Voltage
10 mV of Overdrive, ISOURCE = 2.0 mA
3.5
−
−
Minimum Output Voltage
10 mV of Overdrive, ISINK = 2.0 mA
−
−
1.0
V
Output Source Current (Note 3)
10 mV of Overdrive, VOUT = 3.5 V
−
2
−
mA
Output Sink Current (Note 3)
10 mV of Overdrive, VOUT = 1.0 V
−
2
−
mA
V/ms
V
DIFFERENTIAL SUMMING AMPLIFIERS (VDD & VDDNB)
VS− Input Bias Current
VS− Voltage at 0 V
33
mA
VS+ Input Resistance
DRVON = Low
1.0
kW
VS+ Input Bias Voltage
DRVON = High
7
DRVON = Low
0.37
DRVON = High
0.05
V
VS+ Input Voltage Range (Note 3)
−0.3
−
3.0
V
VS− Input Voltage Range (Note 3)
−0.3
−
0.3
V
−3dB Bandwidth (Note 3)
CL = 80 pF to GND, RL = 10 kW to GND
15
MHz
DC gain, VS+ to DIFFOUT
VS+ to VS− = 0.5 V to 2.35 V
0.982
1.0
1.022
V/V
DAC Accuracy (Measured at VS+)
Closed Loop Measurement, Error Amplifier Inside the
Loop.
1.0125 V v VDAC v 1.5500 V
0.8000 V v VDAC v 1.0000 V
12.5 mV v VDAC v 0.8000 V
−0.5
−5
−8
−
−
−
0.5
5
8
%
mV
mV
Slew Rate
DVIN = 100 mV, DVOUT = 1.3 V−1.2 V
10
Maximum Output Voltage
ISOURCE = 2 mA
Minimum Output Voltage
ISINK = 2 mA
Output source current (Note 3)
VOUT = 3 V
2.0
mA
Output sink current (Note 3)
VOUT = 0.5 V
2.0
mA
V/ms
2.0
V
0.5
V
DROOP AMPLIFIERS (VDD & VDDNB)
Gain from Current Sense Input to
Droop Amplifier Output
0 mV < (CSx − CSxN) < 60 mV
Droop Amplifier DC Output Voltage
CSx = CSxN = 1.3 V
Slew Rate
CL = 20 pF to GND, RL = 1 kW to GND
Maximum Output Voltage
ISOURCE = 4.0 mA
Minimum Output Voltage
ISINK = 1.0 mA
Output Source Current (Note 3)
VOUT = 3.0 V
Output Sink Current (Note 3)
VOUT = 1.0 V
5.7
6.0
6.3
1.3
−
5.0
3.0
−
−
V/V
V
−
V/ms
−
−
V
−
1.0
V
4.0
−
mA
1.0
−
mA
3. Guaranteed by design. Not production tested.
4. For guaranteed Phase Shed Count upon ENABLE assertion, set the PSI_L pin voltage range between the values shown for Min and
Max per the intended phase shed count.
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8
NCP6251
ELECTRICAL CHARACTERISTICS (Unless otherwise stated: 0°CvTAv70°C; 4.75 VvVCCv5.25 V; All DAC Codes; CVCC = 0.1 mF)
Parameter
Test Conditions
Min
Typ
Max
Unit
−50
−
50
nA
Common Mode Input Voltage Range
−0.3
−
2.6
V
Differential Mode Input Voltage
Range (Note 3)
−120
−
120
mV
CURRENT SENSE AMPLIFIERS (VDD & VDDNB)
Input Bias Current
CSx = CSxN = 1.4 V
Input Offset Voltage (Note 3)
CSx = CSxN = 1.00 V
−1.0
−
1.0
mV
Gain from Current Sense Input to
PWM Comparator
0 mV < (CSx − CSxN) < 60 mV
5.0
6.0
7.0
V/V
−
1.3
−
V
3.0
−
−
V
−
0.7
V
INTERNAL OFFSET VOLTAGE
Voltage at Error Amplifier Non−Inverting Inputs
DRVON & NB_DRVON
Output Voltage (High)
Sourcing 500 mA
Output Voltage (Low)
Sinking 500 mA
−
Delay Time
Propagation Delays
−
10
−
ns
Active Internal Pull−up Resistance
Sourcing 500 mA
−
2.0
−
kW
Active Internal Pull−down Resistance
Sinking 500 mA
−
150
−
W
Rise Time
CL (PCB) = 20 pF, DVOUT = 10% to 90%
−
130
−
ns
Fall Time
CL (PCB) = 20 pF, DVOUT = 10% to 90%
−
15
−
ns
100
−
900
kHz
VDD PWM OSCILLATOR
Switching Frequency Range
Switching Frequency Accuracy
2− or 4−phase
ROSC = 49.9 kW
ROSC = 24.9 kW
ROSC = 10 kW
196
380
760
−
−
−
226
420
981
kHz
Switching Frequency Accuracy
3−phase
ROSC = 49.9 kW
ROSC = 24.9 kW
ROSC = 10 kW
196
380
760
−
−
−
226
420
981
kHz
ROSC Output Voltage
10 mA ≤ IROSC ≤ 200 mA
1.94
2.0
2.06
V
−
1.25
−
x fVDD
VDDNB PWM OSCILLATOR
Switching Frequency
PWM COMPARATORS (VDD & VDDNB)
Minimum Pulse Width (Note 3)
FSW = 800 kHz
−
30
−
ns
Propagation Delay (Note 3)
$20 mV of Overdrive
−
10
−
ns
Magnitude of the PWM Ramp
−
1.0
−
V
0% Duty Cycle
COMP Voltage at which the PWM Outputs Remain
LOW
−
0.2
−
V
100% Duty Cycle
COMP Voltage at which the PWM Outputs Remain
HIGH
−
1.2
−
V
PWM Phase Angle Error
Between Adjacent Phases
+15
°
−15
PWRGOOD OUTPUT
PWRGOOD Output Voltage (Low)
IPGD = 5 mA
−
−
0.4
V
PWRGOOD Rise Time
External Pullup of 1 kW to 5 V CTOTAL = 45 pF, DVOUT
= 10% to 90%
−
125
−
ns
PWRGOOD High−State Leakage
VPWRGOOD = 5.25 V
−
−
1
mA
3. Guaranteed by design. Not production tested.
4. For guaranteed Phase Shed Count upon ENABLE assertion, set the PSI_L pin voltage range between the values shown for Min and
Max per the intended phase shed count.
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9
NCP6251
ELECTRICAL CHARACTERISTICS (Unless otherwise stated: 0°CvTAv70°C; 4.75 VvVCCv5.25 V; All DAC Codes; CVCC = 0.1 mF)
Parameter
Test Conditions
Min
Typ
Max
Unit
PWRGOOD OUTPUT
PWRGOOD Upper Threshold
VOUT Increasing, DAC = 1.3 V (Wrt DAC)
−
300
−
mV
PWRGOOD Lower Threshold
VOUT Decreasing, DAC = 1.3 V
−
350
−
mV
3.0
−
VCC
V
PWM OUTPUTS (VDD & VDDNB)
Output Voltage (High)
Sourcing 500 mA
Output Voltage (Low)
Sinking 500 mA
−
−
0.15
V
Rise and Fall Times
CL = 50 pF, 0.7 V to 3.0 V or 3.0 V to 0.7 V
−
15
−
ns
Tri−State Output Leakage
Gx = 2.5 V (x = 1−4 or NB)
−1.5
−
1.5
mA
Output Impedance − HIGH or LOW
State
Resistance to VCC or GND
−
50
−
W
Gate Pin Source Current
−
80
−
mA
Gate Pin Threshold Voltage
−
250
−
mV
Phase Detect Timer
−
20
−
ms
0.64
0.8
0.96
mV/ms
−
3.25
−
mV/ms
VDD REGULATOR 2/3/4 PHASE DETECTION
SLEW RATE LIMITERS
Soft−Start Slew Rate
In Any Mode During Soft−Start
Slew Rate Limit
In Any Mode after Soft−Start Completes
VID INPUTS (Note: In SVI Mode, VID[2] = Bidirectional “SVD’ Line and VID[3] = “SVC” Clock Input supporting AMD’s recommendation
in either fast−mode I2C or high−speed mode I2C)
VID Input Voltage (High)
VHIGH
0.9
−
−
V
VID Input Voltage (Low)
VLOW
−
−
0.6
V
VID Hysteresis
VHIGH − VLOW or VLOW − VHIGH
−
100
−
mV
Input Pulldown Current
VIN = 0.6 V − 1.9 V
−
15
−
mA
SVD Output Voltage (Low)
In SVI Mode, ISINK = 5 mA
0
−
0.25
V
2.0
−
−
V
ENABLE INPUT
ENABLE Input Voltage (High)
VHIGH
ENABLE Input Voltage (Low)
VLOW
−
−
0.8
V
Enable Hysteresis
Low − High or High − Low
−
200
−
mV
Enable Input Pull−Up Current
Internal Pullup to VCC
−
15
−
mA
VFIXEN INPUT (Active−Low Input)
VFIXEN Input Voltage (High)
VHIGH
0.9
−
−
V
VFIXEN Input Voltage (Low)
VLOW
−
−
0.6
V
VFIXEN Hysteresis
Low − High or High − Low
VFIXEN Input Pull−Up Current
Internal Pullup to VCC
100
mV
−
15
−
mA
PSI_L (Power Saving Phase Shed and Control, Active Low) (This pin is used in PVI mode only)
PSI_L Phase Shed Count (Note 4)
Before Enable Assertion, No Phase Shedding while
PSI_L Active
−
−
0.6
V
PSI_L Phase Shed Count (Note 4)
Before ENABLE Assertion, Phase Shed to 2 Phases
0.9
−
1.1
V
PSI_L Phase Shed Count (Note 4)
Before ENABLE Assertion, Phase Shed to 1 Phase
1.3
−
−
V
PSI_L Input Voltage (High)
After Soft−Start, VHIGH
0.9
−
−
V
PSI_L Input Voltage (Low)
After Soft−Start, VLOW
−
−
0.6
V
PSI_L Hysteresis
After Soft−Start, VHIGH − VLOW or VLOW − VHIGH
100
mV
3. Guaranteed by design. Not production tested.
4. For guaranteed Phase Shed Count upon ENABLE assertion, set the PSI_L pin voltage range between the values shown for Min and
Max per the intended phase shed count.
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NCP6251
ELECTRICAL CHARACTERISTICS (Unless otherwise stated: 0°CvTAv70°C; 4.75 VvVCCv5.25 V; All DAC Codes; CVCC = 0.1 mF)
Parameter
Test Conditions
Min
Typ
Max
Unit
5.7
6.0
6.3
V/V
−
−
0.5
mA
0.2
−
2.0
V
−
30
−
mV
−
600
−
ns
−
1.0
−
V
−
1.3
−
0
−
800
mV
VDAC
+ 220
VDAC
+ 235
VDAC
+ 250
mV
VCCA UVLO Start Threshold
4.0
4.25
4.5
V
VCCA UVLO Stop Threshold
3.8
4.05
4.3
V
CURRENT LIMIT
Current Sense Amp to ILIM Gain
20 mV < (CSx − CSxN) < 60 mV (CS inputs tied)
ILIM Pin Input Bias Current
ILIM Pin Working Voltage Range
(Note 3)
ILIM Offset Voltage
Offset extrapolated to CSx−CSxN = 0 V, and referred
to the ILIM pin
Delay
VDDNB Current Limit Coefficient
= N x VNBILIM /VILIM, where N = number of VDD
phases, and VNBILIM is the equivalent voltage
threshold for NB Current Limit resulting from VILIM.
ILIM2 to ILIM1 Ratio
OFFSET INPUTS (VDD & VDDNB)
Output Offset Voltage Above VDAC
OUTPUT OVERVOLTAGE PROTECTION (VDD & VDDNB)
In normal operation, with no VID changes
Over Voltage Threshold
VCCA UNDERVOLTAGE PROTECTION
VCCA UVLO Hysteresis
200
mV
INPUT SUPPLY CURRENT
ENABLE held Low, No PWM operation
−
25
35
mA
12VMON (High Threshold)
8
8.5
9
V
12VMON (Low Threshold)
7
7.5
8
V
VCC Operating Current
12VMON
12VMON Hysteresis
Low − High or High − Low
1.0
V
3. Guaranteed by design. Not production tested.
4. For guaranteed Phase Shed Count upon ENABLE assertion, set the PSI_L pin voltage range between the values shown for Min and
Max per the intended phase shed count.
TYPICAL CHARACTERISTICS
1.5
EN, ENABLE THRESHOLD
VOLTAGE (V)
2.03
SS TIME (ms)
2.01
1.99
1.97
1.95
0
25
50
1.4
1.2
Enable Decreasing Voltage
1.1
1.0
75
Enable Increasing Voltage
1.3
0
25
50
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 1. SS Time vs. Temperature
Figure 2. Enable Threshold Voltage vs.
Temperature
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75
NCP6251
231.1
25.8
230.8
DETECT THRESHOLD (mV)
26.1
25.5
25.2
24.9
24.6
24.3
VCC UVLO THRESHOLD VOLTAGE (V)
0
25
50
230.2
229.9
229.6
229.3
229.0
75
0
25
50
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 3. ICC Current vs. Temperature
Figure 4. 2/3/4 Phase Detection Threshold vs.
Temperature
75
2.009
4.5
2.008
VCCP Increasing Voltage
ROSC VOLTAGE (V)
VCCP UVLO THRESHOLD VOLTAGE (V)
24.0
230.5
4.0
VCCP Decreasing Voltage
3.5
2.007
2.006
2.005
2.004
3.0
0
25
50
50
Figure 5. VCCP Undervoltage Lockout
Threshold Voltage vs. Temperature
Figure 6. ROSC Voltage vs. Temperature
9.0
VCC Increasing Voltage
8.5
8.0
VCC Decreasing Voltage
0
25
TJ, JUNCTION TEMPERATURE (°C)
9.5
7.0
0
TJ, JUNCTION TEMPERATURE (°C)
10
7.5
2.003
75
25
50
75
PWRGOOD THRESHOLD VOLTAGE (mV)
ICC CURRENT (mA)
TYPICAL CHARACTERISTICS
370
PWRGOOD Upper Voltage
360
350
340
330
320
310
PWRGOOD Lower Voltage
0
25
50
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 7. 12VMON Undervoltage Lockout
Threshold Voltage vs. Temperature
Figure 8. PWRGOOD Voltage vs. Temperature
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75
NCP6251
Functional Description
General
Gate Driver Outputs and 2/3/4 Phase Operation
NCP6251 is a universal CPU hybrid power Controller
compatible with both Parallel VID interface (PVI) and
Serial VID interface (SVI) protocols for AMD Processors.
The Controller implements a single−phase control
architecture to provide the Northbridge (NB) voltage on the
same chip. For the CORE section, programmable 2− to−4
phase featuring Dual−Edge multiphase architecture is
implemented. It embeds two independent controllers for
CPU CORE and the integrated NB, each one with its set of
protections.
The NCP6251 incorporates differential voltage sensing,
differential phase current sensing, optional load−line
voltage positioning, and programmable VDD and VDDNB
offsets to provide accurately regulated power parallel− and
serial−VID AMD processors. Dual−edge multiphase
modulation provides the fastest initial response to dynamic
load events.
NCP6251 also supports V_FIX mode for board debug and
testing. In this particular configuration the SVI bus is used
as a static bus configuring four operative voltages (through
SVC and SVD) for both the sections and ignoring any
serial−VID command.
NCP6251 is able to detect which kind of CPU is connected
and configures itself to work as a Single−Plane PVI
controller or Dual−Plane SVI controller.
The part can be configured to run in 2−, 3−, or 4−phase
mode. In 2−phase mode, phases 1 and 3 should be used to
drive the external gate drivers, G2 and G4 must be grounded.
In 3−phase mode, gate output G4 must be grounded. In
4−phase mode all 4 gate outputs are used as shown in the
4−phase Applications Schematic. The Current Sense inputs
of unused channels should be connected to GND or to VDD.
Please refer to table “PIN CONNECTIONS vs. PHASE
COUNTS” for details.
Differential Current Sense Amplifiers and Summing
Amplifier
Four differential amplifiers are provided to sense the
output current of each phase. The inputs of each current
sense amplifier must be connected across the current sensing
element of the phase controlled by the corresponding gate
output (G1, G2, G3, or G4). If a phase is unused, the
differential inputs to that phase’s current sense amplifier
must be shorted together and connected to the GND or to
VDD.
The current signals sensed from inductor DCR are fed into
a summing amplifier to have a summed−up output. The
outputs of current sense amplifiers control three functions.
First, the summing current signal of all phases will go
through DROOP amplifier and join the voltage feedback
loop for output voltage positioning. Second, the output
signal from DROOP amplifier also goes to ILIM amplifier
to monitor the output current limit. Finally, the individual
phase current contributes to the current balance of all phases
by offsetting their ramp signals of PWM comparators.
Remote Output Sensing Amplifier (RSA)
A true differential amplifier allows the NCP6251 to measure
VCore voltage feedback with respect to the VCore ground
reference point by connecting the VCore reference point to
VSP, and the VCore ground reference point to VSN. This
configuration keeps ground potential differences between the
local controller ground and the VCore ground reference point
from affecting regulation of VCore between VCore and
VCore ground reference points. The RSA also subtracts the
DAC (minus VID offset) voltage, thereby producing an
unamplified output error voltage at the DIFFOUT pin. This
output also has a 1.3 V bias voltage as the floating ground to
allow both positive and negative error voltages.
Oscillator and Triangle Wave Generator
The controller embeds a programmable precision
dual−Oscillator: one section is used for the CORE and it is
a multiphase programmable oscillator managing equal
phase−shift among all phases and the other section is used
for the NB section. The oscillator’s frequency is
programmed by the resistance connected from the ROSC
pin to ground. The user will usually form this resistance
from two resistors in order to create a voltage divider that
uses the ROSC output voltage as the reference for creating
the current limit setpoint voltage. The oscillator frequency
range is 100 kHz per phase to 1.0 MHz per phase. The
oscillator generates up to 4 symmetrical triangle waveforms
with amplitude between 1.3 V and 2.3 V. The triangle waves
have a phase delay between them such that for 2−, 3− and
4−phase operation the PWM outputs are separated by 180,
120, and 90 angular degrees, respectively.
When the NB phase is enabled, in order to ensure that the
VDDNB oscillator does not accidentally lock to the VDD
oscillator, the VDDNB oscillator will free−run at a
frequency which is nominally 1.25 ratio of fVDD.
Precision Programmable DAC
A precision programmable DAC is provided and system
trimmed. This DAC has 0.6% accuracy over the entire
operating temperature range of the part. The NCP6251 is a
Hybrid controller which supports both a six bit parallel VID
interface (PVI) and a seven bit serial VID interface (SVI).
The NCP6251 allows manufacturers to build a motherboard
that will accommodate either parallel or serial VID
processors in the same socket.
High Performance Voltage Error Amplifier
The error amplifier is designed to provide high slew rate
and bandwidth. Although not required when operating as the
controller of a voltage regulator, a capacitor from COMP to
VFB is required for stable unity gain test configurations.
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NCP6251
CPU Support
NCP6251 is able to detect the CPU it is going to supply
and configure itself to PVI or SVI mode. When in PVI mode,
to address the CORE section the NCP6251 uses VID[5:0].
When in SVI mode NCP6251 uses VID2 and VID3 alone for
SVC and SVD information respectively. Whether the
controller is controlled by the serial or parallel interface is
determined by sampling the VID1 line at the time that the
voltage regulator enable line is asserted; if the VID1 line is
high when Enable is asserted, the voltage regulator starts in
PVI mode, otherwise the voltage regulator starts in SVI
mode.
•
•
•
•
PVI − Parallel Interface
PVI is a 6−bit wide parallel interface to address the CORE
Section reference. NB is kept in HiZ mode. Parallel mode
operation is depicted in Figure 9. Voltage identifications for
the 6bit AMD mode is given in Table 2.
The normal PVI startup sequence for the NCP6251 is as
follows:
• 5 V is applied to the VCCA and VCCB pins to power
the NCP6251 and 12 V is applied to 12VMON.
• The NCP6251 samples the load on the G4 and G2 pins.
If these pins are tied to ground the operating mode will
be altered from four phase mode, to three phase, or two
phase operation.
• The system power sequence logic asserts the NCP6251
ENABLE pin:
DC IN
− The NCP6251 will sample the VID1 line to
determine whether to start in SVI or PVI mode.
PVID mode is determined when VID1 = High.
− The NCP6251 samples the voltage on the PSI_L pin
in order to determine the desired operating
configuration during power saving mode.
− The Boot VID is captured from decoding the
voltages on the VID[0:5].
The NCP6251 VDD regulator will soft−start and ramp
to the initial Boot VID. The VDDNB regulator remains
off (high−Z output).
PWRGOOD is asserted by the NCP6251.
PWROK is not used in PVID mode.
The NCP6251 will accept new VID codes on the
parallel VID interface (See Table 2).
See Figure 9 for details.
Table 1. Metal VID/BOOT VID
Output Voltage
SVC
SVD
Pre−PWROK Metal VID
0
0
1.1 V
0
1
1.0 V
1
0
0.9 V
1
1
0.8 V
With ENABLE assertion, the PSI_L Phase Shed Strategy is Locked
therefore Voltages on PSI_L must be stable prior to ENABLE assertion.
VR Turn−On
Command
VDDIO
VR Turn−Off
Command
ENABLE
BOOT VID MSB
VID[5]
VID[1] High at Rise of Enable Selects PVI Operation
PVIEN/
VID[1]
BOOT VID LSB
VID[0]
At end of soft−start, PSI_L can be asserted.
VDD ONLY
[NDDNB N/A]
PWRGOOD
PWROK IS N/A
Output Rises to BOOT
VID at SS Rate
Soft−Start is
Complete
Further VDD Transition(s)
at Regular Slew Rate
PWRGOOD
De−Assertion
Occurs on
Faults Only
Figure 9. Power Up Sequences in Parallel Mode Operation
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VR Turn−Off Command
Forces PWRGOOD Low
NCP6251
Table 2. SIX−BIT PARALLEL VID CODES in PVI Modes
SVID[5:0]
VOUT (V)
SVID[5:0]
VOUT (V)
SVID[5:0]
VOUT (V)
SVID[5:0]
VOUT (V)
00_0000
1.5500
01_0000
1.1500
10_0000
0.7625
11_0000
0.5625
00_0001
1.5250
01_0001
1.1250
10_0001
0.7500
11_0001
0.5500
00_0010
1.5000
01_0010
1.1000
10_0010
0.7375
11_0010
0.5375
00_0011
1.4750
01_0011
1.0750
10_0011
0.7250
11_0011
0.5250
00_0100
1.4500
01_0100
1.0500
10_0100
0.7125
11_0100
0.5125
00_0101
1.4250
01_0101
1.0250
10_0101
0.7000
11_0101
0.5000
00_0110
1.4000
01_0110
1.0000
10_0110
0.6875
11_0110
0.4875
00_0111
1.3750
01_0111
0.9750
10_0111
0.6750
11_0111
0.4750
00_1000
1.3500
01_1000
0.9500
10_1000
0.6625
11_1000
0.4625
00_1001
1.3250
01_1001
0.9250
10_1001
0.6500
11_1001
0.4500
00_1010
1.3000
01_1010
0.9000
10_1010
0.6325
11_1010
0.4375
00_1011
1.2750
01_1011
0.8750
10_1011
0.6250
11_1011
0.4250
00_1100
1.2500
01_1100
0.8500
10_1100
0.6125
11_1100
0.4125
00_1101
1.2250
10_1101
0.8250
10_1101
0.6000
11_1101
0.4000
00_1110
1.2000
01_1110
0.8000
10_1110
0.5875
11_1110
0.3875
00_1111
1.1750
01_1111
0.7750
10_1111
0.5750
11_1111
0.3750
SVI − Serial Interface
SVI is a two wire, Clock and Data, bus that connects a
single master (CPU) to one NCP6251. The master initiates
and terminates SVI transactions and drives the clock, SVC,
and the data SVD, during a transaction. The slave receives
the SVI transactions and acts accordingly. SVI wire protocol
is based on fast−mode I2C.
PWROK is proprietary of the SVI protocol and is
considered at start−up. The SVI mode operation is explained
in Figure 10. The VID codes from the decoded SVI value are
given in Table 3.
The normal SVI startup sequence for the NCP6251 is as
follows:
• 5 V is applied to the VCCA and VCCB pins to power
the NCP6251 and 12 V is applied to 12VMON.
• The NCP6251 samples the load on the G4 and G2 pins.
If these pins are tied to ground the operating mode will
be altered from four phase mode, to three phase, or two
phase operation.
• The system power sequence logic asserts the NCP6251
ENABLE pin:
•
•
•
•
•
− The NCP6251 will sample the VID1 line to
determine whether to start in SVI or PVI mode.
SVID mode is determined when VID1 = Low.
− The NCP6251 samples the voltage on the PSI_L pin
in order to determine the desired operating
configuration during power saving mode.
− The Boot VID is captured from decoding the
voltages on the VID3/SVC and VID2/SVD pins per
Table 1 and stored.
The NCP6251 will start the VDD and VDDNB
regulators. Both regulators will soft start and ramp to
the Boot VID Voltage (See Table 1).
The NCP6251 asserts PWRGOOD.
The system asserts PWROK The system processor will
hold the boot VID voltage for at least 10us after
PWROK signal is asserted
Now the NCP6251 can accept new SVID codes on the
serial VID interface (See Table 3).
If the system should de−assert PWROK, then the
NCP6251 will reset the Core and Northbridge VIDs
and regulate at the Boot VID voltage.
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NCP6251
Table 3. SEVEN−BIT SERIAL VID CODES for SVI Mode
SVID[6:0]
VOUT (V)
SVID[6:0]
VOUT (V)
SVID[6:0]
VOUT (V)
SVID[6:0]
VOUT (V)
000_0000
1.5500
010_0000
1.1500
100_0000
0.7500
110_0000
0.3500
000_0001
1.5375
010_0001
1.1375
100_0001
0.7375
110_0001
0.3375
000_0010
1.5250
010_0010
1.1250
100_0010
0.7250
110_0010
0.3250
000_0011
1.5125
010_0011
1.1125
100_0011
0.7125
110_0011
0.3125
000_0100
1.5000
010_0100
1.1000
100_0100
0.7000
110_0100
0.3000
000_0101
1.4875
010_0101
1.0875
100_0101
0.6875
110_0101
0.2875
000_0110
1.4750
010_0110
1.0750
100_0110
0.6750
110_0110
0.2750
000_0111
1.4625
010_0111
1.0625
100_0111
0.6625
110_0111
0.2625
000_1000
1.4500
010_1000
1.0500
100_1000
0.6500
110_1000
0.2500
000_1001
1.4375
010_1001
1.0375
100_1001
0.6325
110_1001
0.2375
000_1010
1.4250
010_1010
1.0250
100_1010
0.6250
110_1010
0.2250
000_1011
1.4125
010_1011
1.0125
100_1011
0.6125
110_1011
0.2125
000_1100
1.4000
010_1100
1.0000
100_1100
0.6000
110_1100
0.2000
000_1101
1.3875
010_1101
0.9875
100_1101
0.5875
110_1101
0.1875
000_1110
1.3750
010_1110
0.9750
100_1110
0.5750
110_1110
0.1750
000_1111
1.3625
010_1111
0.9625
100_1111
0.5625
110_1111
0.1625
001_0000
1.3500
011_0000
0.9500
101_0000
0.5500
111_0000
0.1500
001_0001
1.3375
011_0001
0.9375
101_0001
0.5375
111_0001
0.1375
001_0010
1.3250
011_0010
0.9250
101_0010
0.5250
111_0010
0.1250
001_0011
1.3125
011_0011
0.9125
101_0011
0.5125
111_0011
0.1125
001_0100
1.3000
011_0100
0.9000
101_0100
0.5000
111_0100
0.1000
001_0101
1.2875
011_0101
0.8875
101_0101
0.4875
111_0101
0.0875
001_0110
1.2750
011_0110
0.8750
101_0110
0.4750
111_0110
0.0750
001_0111
1.2625
011_0111
0.8625
101_0111
0.4625
111_0111
0.0625
001_1000
1.2500
011_1000
0.8500
101_1000
0.4500
111_1000
0.0500
001_1001
1.2375
011_1001
0.8375
101_1001
0.4375
111_1001
0.0375
001_1010
1.2250
011_1010
0.8250
101_1010
0.4250
111_1010
0.0250
001_1011
1.2125
011_1011
0.8125
101_1011
0.4125
111_1011
0.0125
001_1100
1.2000
011_1100
0.8000
101_1100
0.4000
111_1100
OFF
001_1101
1.1875
011_1101
0.7875
110_1101
0.3875
111_1101
OFF
001_1110
1.1750
011_1110
0.7750
101_1110
0.3750
111_1110
OFF
001_1111
1.1625
011_1111
0.7625
101_1111
0.3625
111_1111
OFF
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NCP6251
DC IN
With ENABLE assertion, the PSI_L Phase Shed Strategy is Locked therefore
Voltages on PSI_L must be stable prior to ENABLE assertion.
VR Turn−On
Command
VDDIO
VR Turn−Off
Command
ENABLE
PVIEN/
VID[1]
VID[1] Low at Rise of Enable Selects SVI Operation
BOOT VID MSB
SVC/
VID[3]
SVD/
VID[2]
VR Turn−Off
Command Forces
PWRGOOD Low
BOOT VID LSB
VDD and VDDNB
Soft−Start is
Complete
PWRGOOD
Possible PWRGOOD
De−Assertion
CPU Can Begin
Serial Data Xfer
PWROK
System Power Fault − Revert to BOOT VID
Resume Serial
VID Transactions
At end of soft−start, PSI_L can be asserted
through the SVID protocal.
Outputs Rise to BOOT
VID at SS Rate
PWRGOOD De−Assertion
Causes System PWROK
De−Assertion
Figure 10. Power−Up Sequence in Serial Mode Operation
• The system power sequence logic asserts the NCP6251
Hardware Jumper Override − V_FIX
VFIX is an active low pin and when it is pulled low, the
controller enters V_FIX mode. The voltage regulator can be
powered when an external SVI bus master is not present.
When in VFIX mode, all of the voltage regulator’s output
voltages will be governed by the information shown in
Table 4, regardless of the state of PWROK. VFIX mode is
for debug only. If VFIX mode is necessary for processor
bring−up, VFIXEN, SVC, and SVD should be connected
with jumpers to either ground or VDDIO through suitable
pull−up resistors. SVC and SVD are considered as static
VID and the output voltage will change according to their
status.
•
•
Table 4. SVI VFIX VID CODES (TWO−BIT PARALLEL)
SVC
SVD
VOUT (V)
0
0
1.4
0
1
1.2
1
0
1.0
1
1
0.8
•
•
•
The normal VFIXEN startup sequence for the NCP6251
is as follows:
• 5 V is applied to the VCCA and VCCB pins to power
the NCP6251 and 12 V is applied to 12VMON.
• The NCP6251 samples the load on the G4 and G2 pins.
If these pins are tied to ground the operating mode will
be altered from four phase mode, to three phase, or two
phase operation.
ENABLE pin:
− The NCP6251 will sample the VID1 line to
determine whether to start in SVI or PVI mode.
− The NCP6251 samples the voltage on the PSI_L pin
in order to determine the desired operating
configuration during power saving mode.
− The Boot VID is dependent on SVI or PVI mode
startup.
The NCP593A VDD regulator (and VDDNB if in SVID
mode) will soft−start and ramp to the initial Boot VID.
VFIXEN mode is entered once VFIXEN is asserted and
the VDD and VDDNB regulators will regulate to the
VFIXEN VID.
VFIXEN VID is captured from decoding the voltages
on the VID3/SVC and VID2/SVD pins per Table 4.
If VFIXEN is asserted prior to the VID controller
reaching the Boot VID, the VID controller will move to
the VFIXEN VID.
If VFIXEN is de−asserted, the evice PORs. This occurs
independent of ENABLE.
PWROK De−Assertion
Anytime PWROK de−asserts while EN is asserted, the
controller uses the previously stored BOOT VID and
regulates all planes to that level performing an on−the−fly
transition to that level. PWRGOOD remains asserted in this
process.
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NCP6251
Power Saving Indicator (PSI_L) and Phase Shedding
the VDRP minus offset voltage. Internally there are two
overcurrent thresholds based on the ILIM pin voltage. If the
current information exceeds one of the thresholds, the
overcurrent latch will be set either immediately (ILIM2) or
with a delay of 50 ms (ILIM1). The outputs are pulled low,
and the soft−start is pulled low. The outputs will remain
disabled until the VCC voltage is removed and re−applied, or
the ENABLE input is brought low and then high.
NB overcurrent is handled in similar way as the global
CORE overcurrent. The total output current is compared
with Ilimit/Nphase. When overcurrent occurs in the NB,
NB−DRVON is pulled low.
An AMD PVID processor provides an output signal to the
NCP6251 controller’s PSI_L input to indicate when the
processor is in a low power state. An AMD SVID processor
indicates PSI_L mode through the SVID protocol. The
NCP6251 uses PSI_L assertion to maximize efficiency at
light loads. When PSI_L is asserted, the PSI_L function will
be enabled, and the NCP6251 will run with a reduced phase
count. The number of phases in PSI_L mode is determined
by the voltage level present on the PSI_L input upon
ENABLE assertion. This detection of phase count applies
for both PVID and SVID AMD processors.
Protection Features:
The NCP6251 handles many protection features.
Undervoltage lockout, Over current shutdown,
Overvoltage, Under voltage, Soft−Start etc are the main
features. All the fault responses of the NCP6251 are listed
in Table 5.
Output Overvoltage and Undervoltage Protection and
Power Good Monitor
An output voltage monitor is incorporated. During normal
operation, if the output voltage is 250 mV over the DAC
voltage, the PWRGOOD goes low, the DRVON signal
remains high, the PWM outputs are set low. The outputs will
remain disabled until the VCC voltage is removed and
reapplied. Every time the OV is triggered it will increment
the OV counter. If the counter reaches a count of 16 then the
OV condition will latch into a permanent OV state. It will
require POR or disable/enable to restart. Prior to latching if
the OV condition goes away then normal operation will
resume. An OV decrement counter is also incorporated. It
consists of a free−running clock which runs at 8x the PWM
frequency. So essentially every 4096 PWM cycles the OV
counter will decrement. For example, for a max PWM
frequency of 1 MHz, the counter decrements roughly every
4 ms and for a PWM frequency of 400 kHz, it would be
about every 10 ms. During normal operation, if the output
voltage falls more than 350 mV below the DAC setting, the
PWRGOOD pin will be set low until the output voltage rises.
Undervoltage Lockout
An undervoltage lockout (UVLO) senses the VCC and
VCCP input. During powerup, the input voltage to the
controller is monitored, and the PWM outputs and the
soft−start circuit are disabled until the input voltage exceeds
the threshold voltage of the UVLO comparator. The UVLO
comparator incorporates hysteresis to avoid chattering,
since VCC is likely to decrease as soon as the converter
initiates soft−start.
Overcurrent Shutdown
A programmable overcurrent function is incorporated
within the IC. A comparator and latch make up this function.
The inverting input of the comparator is connected to the
ILIM pin. The voltage at this pin sets the maximum output
current the converter can produce. The ROSC pin provides
a convenient and accurate reference voltage from which a
resistor divider can create the overcurrent setpoint voltage.
Although not actually disabled, tying the ILIM pin directly to
the ROSC pin sets the limit above useful levels − effectively
disabling overcurrent shutdown. The comparator
noninverting input is the summed current information from
Soft−Start
The NCP6251 ramps VDD (and VDDNB in SVID mode)
to the Boot VID at a soft−start rate of 0.8 mV/ms typical.
Upon receiving a PVID or SVID code (after PWROK
assertion) the outputs ramp to the final DAC setting at the
Dynamic VID slew rate of 3.25 mV/ms. Typical soft−start
sequence timing is shown in Figure 11.
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NCP6251
VID
Setting
VOLTAGE
Boot
Voltage
NCP6251 Soft−Start
Slew Rate 0.8 mV/ms
NCP6251 Internal
Dynamic VID Slew
Rate 3.25 mV/ms
TIME
Figure 11. Soft Start Sequence to VCore
Table 5. FAULT RESPONSES
PWM OUTPUT(s)
PWRGOOD
DRVON
(VDD)
DRVON (NB)
VDD Global
OCP (ILIM1)
All to High−Z
Latched Low
Latched Low
Latched Low
Cycle
ENABLE
or +5 V and
+12 V
Latched if the VDD rail current is over ILIM1 (less than
ILIM2) for 50 ms
VDD Global
OCP Immediately
(ILIM2)
All to High−Z
Latched Low
Latched Low
Latched Low
Cycle
ENABLE
or +5 V and
+12 V
Latched immediately if the
VDD rail current is over ILIM2
NB OCP
All to High−Z
Latched Low
Latched Low
Latched Low
Cycle
ENABLE
or +5 V and
+12 V
Output OVP
−
Infrequent
Held Low for
duration of
OV
Held Low for
duration of
OV plus
500 ms
Unaffected
Unaffected
Output OVP
−
Frequent
Latched Low
Latched Low
Unaffected
Unaffected
Output UV
Monitor
Unaffected
Held Low for
duration of
UV
Unaffected
Unaffected
Unused
Phase of
VDD
Regulator
Set to
High−Z
Unaffected
Unaffected
Unaffected
VDDNB
Disabled
Set to
High−Z
Unaffected
by NB status
Unaffected
Latched Low
5 V UVLO
All to High−Z
Held Low
Low until 5 V
and 12 V are
OK
12 V UVLO
All to High−Z
Held Low
Low until 5 V
and 12 V are
OK
CONDITION
NOTES
“Infrequent” = fewer than 17
events per 4096/Fpwm
seconds (e.g., 4.096 ms at
Core PWM = 1 MHz)
Cycle
ENABLE,
VCC (5 V) or
12 VMON
“Frequent” = 17 or more
events per 4096/Fpwm
seconds (e.g., 4.096 ms at
Core PWM = 1 MHz)
Low until 5 V
and 12 V are
OK
Raise +5 V
above UVLO
Threshold
5 V and 12 V UVLO are the
only modes which will force
re−evaluating the phase
count.
Low until 5 V
and 12 V are
OK
Raise +12 V
above UVLO
Threshold
5 V and 12 V UVLO are the
only modes which will force
re−evaluating the phase
count.
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RESET
METHOD
NCP6251
Table 5. FAULT RESPONSES
CONDITION
PWM OUTPUT(s)
PWRGOOD
DRVON
(VDD)
DRVON (NB)
RESET
METHOD
NOTES
DRVON is
Pulled Low
by External
Means
Unaffected
(See Notes
³)
Held Low
While Low a
weak pull−up
turns on
Unaffected
Address
underlying
cause, and let
DRVON go
High
VDD will try to regulate to
0 V. DRVON low will cause
VDD MOSFETs to turn off.
Both VDD & VDDNB will go
through a SS upon recovery.
NB_DRVON
is Pulled
Low by
External
Means
Unaffected
(See Notes
³)
Held Low
Unaffected
While Low a
weak pull−up
turns on
Address
underlying
cause, and let
NB_DRVON
go High
VDDNB will try to regulate to
0 V. With NB_DRVON Low,
all VDDNB MOSFETs to
turnoff. Both VDD & VDDNB
will go through a SS upon
recovery.
ENABLE is
Low
All to High−Z
Held Low
Held Low
Held Low
Assert
ENABLE High
Cycling ENABLE does not
cause the NCP6251 to re−
evaluate the programmed
number of phases
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NCP6251
Programming the Current Limit and the Oscillator Frequency
proportional to the resistance and frequency is inversely
proportional to the total resistance. The total resistance may
be estimated by Equation 2. This equation is valid for the
individual phase frequency in both three and four phase
mode.
The demo board is set for an operating frequency of
approximately 330 kHz. The ROSC pin provides a 2.0 V
reference voltage which is divided down with a resistor
divider and fed into the current limit pin ILIM. Calculate the
total series resistance to set the frequency and then calculate
the individual RLIM1 and RLIM2 values for the divider.
The series resistors RLIM1 and RLIM2 sink current from
the ILIM pin to ground. This current is internally mirrored
into a capacitor to create an oscillator. The period is
RTOTAL ^ 24686
Fsw−1.1549
30.5 · kW ^ 24686
330−1.1549
(eq. 1)
Figure 12. ROSC vs. Frequency
the expected average maximum temperature of the inductor
windings.
The current limit function is based on the total sensed
current of all phases multiplied by a gain of 6. DCR sensed
inductor current is function of the winding temperature. The
best approach is to set the maximum current limit based on
DCRTmax + DCR25C ·
(1 ) 0.00393 (T max −25))
Calculate the current limit voltage:
ǒ
VILIMIT ^ 6 · IMIN_OCP · DCRTmax )
DCRTmax · Vout
2 · Vin · Fsw
ǒ
· Vin−Vout * (N−1) · Vout
L
L
ǓǓ
(eq. 2)
(eq. 3)
Solve for the individual resistors:
RLIM2 +
VILIMIT · RTOTAL
RLIM1 + RTOTAL−RLIM2
(eq. 4)
2·V
(eq. 5)
Final Equation for the Current Limit Threshold
ILIMIT(Tinductor) ^
ǒ
2 · V · RLIM2
RLIM1)RLIM2
Ǔ
6 · (DCR25C · (1 ) 0.00393(TInductor−25)))
*
ǒ
Vout
· Vin−Vout * (N−1) · Vout
L
L
2 · Vin · Fsw
Ǔ
(eq. 6)
Two Stage Overcurrent Limit
The inductors on the demo board have a DCR at 25°C of
0.75 mW. Selecting the closest available values of 16.9 kW
for RLIM1 and 13.7 kW for RLIM2 yield a nominal
operating frequency of 330 kHz and an approximate current
limit of 152 A at 100°C. The total sensed current can be
observed as a scaled voltage at the VDRP pin added to a
positive, no−load offset of approximately 1.3 V.
NCP6251 will hold two overcurrent limits, ILIM1 is equal
to ILIMIT, it has a delayed latch response (50 ms). ILIM2 is
typically 1.3 x ILIM1 and once triggered, PWM output will
be immediately latched at high impedance.
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NCP6251
OUTPUT OFFSET VOLTAGES
External offset voltages from 0 mv to 800 mV ‘above the DAC’ can be added for the VDD and VDD_NB independently.
Offset is set by a resistor divider from VCC to GND. Output offsets are ratiometric to VCC. As VCC changes, the on−chip scaling
factors change by the same amount:
Offset = 0.8 V x VOFFSET/VCC
For example: For 0 V offset: pin voltage = GND; For 800 mV offset: pin voltage = VCC
Minimum Voffset_IN
(as Vin/VCC)
Typical Voffset_IN
(as Vin/VCC)
Maximum Voffset_IN
(as Vin/VCC)
Resulting Output Offset
Units
0
0
0.046875
0
mV
0.046875
0.06250
0.078125
25
mV
0.078125
0.09375
0.109375
50
mV
0.109375
0.12500
0.140625
75
mV
0.140625
0.15625
0.171875
100
mV
0.171875
0.18750
0.203125
125
mV
0.203125
0.21875
0.234375
150
mV
0.234375
0.25000
0.265625
175
mV
0.265625
0.28125
0.296875
200
mV
0.296875
0.31250
0.328125
225
mV
0.328125
0.34375
0.359375
250
mV
0.359375
0.37500
0.390625
275
mV
0.390625
0.40625
0.421875
300
mV
0.421875
0.43750
0.453125
325
mV
0.453125
0.46875
0.484375
350
mV
0.484375
0.50000
0.515625
375
mV
0.515625
0.53125
0.546875
400
mV
0.546875
0.56250
0.578125
425
mV
0.578125
0.59375
0.609375
450
mV
0.609375
0.62500
0.640625
475
mV
0.640625
0.65625
0.671875
500
mV
0.671875
0.68750
0.703125
525
mV
0.703125
0.71875
0.734375
550
mV
0.734375
0.75000
0.765625
575
mV
0.765625
0.78125
0.796875
600
mV
0.796875
0.81250
0.828125
625
mV
0.828125
0.84375
0.859375
650
mV
0.859375
0.87500
0.890625
675
mV
0.890625
0.90625
0.921875
700
mV
0.921875
0.93750
0.953125
725
mV
0.953125
0.96875
0.984375
750
mV
0.984375
1.00000
VCC+0.3 V
800
mV
The input to the OFFSET pin for the VDD output is encoded by an internal ADC.
The input to the NB_OFFSET pin for the VDDNB output is encoded by the same ADC.
The reference for this ADC is VCC. The ADC’s output is ratiometric to VCC.
Voffset IN represents the voltage applied to the OFFSET or NB_OFFSET pin.
It is intended that these voltages be derived by a resistive divider from VCC.
The recommended total driving impedance is
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