ON NCP81251 Single-phase voltage regulator Datasheet

NCP81251
Single-Phase Voltage
Regulator with SVID
Interface for Computing
Applications
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High Switching Frequency, High
Efficiency, Integrated Power MOSFETs
The NCP81251, a single−phase synchronous buck regulator,
integrates power MOSFETs to provide a high−efficiency and
compact−footprint power management solution for new generation
computing CPUs. The device is able to deliver up to 14 A TDC output
current on an adjustable output with SVID interface. Operating in high
switching frequency up to 1.2 MHz allows employing small size
inductors and capacitors while maintaining high efficiency due to
integrated solution with high performance power MOSFETs.
Current−mode RPM control with feedforward from both input power
supply and output voltage ensures stable operation over wide
operation condition. The NCP81251 is in a QFN48 6 x 6 mm package.
Features
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Meets Intel® Server Specifications
5 V to 20 V Input Voltage Range
1.0 V/1.1 V Fixed Boot Voltage
Adjustable Output Voltage with SVID Interface
Integrated Gate Driver and Power MOSFETs
Up to 14 A TDC Output Current
500 kHz ~ 1.2 MHz Switching Frequency
Current−Mode RPM Control
Programmable SVID Address and ICCMax
Adaptive Voltage Positioning (AVP)
Programmable DVID Feed−Forward to Support Fast DVID
Feedforward Operation for Input Supply Voltage and Output Voltage
Output Over−Voltage and Under−Voltage Protections
External Current Limitation Programming with Inductor Current
Sense
QFN48, 6 x 6 mm, 0.4 mm Pitch Package
This is a Pb−Free Device
MARKING
DIAGRAM
1
1 48
NCP81251
AWLYYWWG
QFN48
CASE 485CJ
NCP81251
A
WL
YY
WW
G
= Specific Device Code
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
ORDERING INFORMATION
Device
NCP81251MNTXG
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 Specification
Brochure, BRD8011/D.
Typical Applications
• Server Applications
© Semiconductor Components Industries, LLC, 2015
September, 2015 − Rev. 1
1
Publication Order Number:
NCP81251/D
48
47
46
45
44
43
42
41
40
39
38
37
EN
VCC
VSP
VSN
DIFFOUT
FB
COMP
FREQ
CSREF
CSSUM
CSCOMP
ILIM
NCP81251
1
VRHOT#
2
SDIO
3
ALERT#
4
SCLK
VCCP 33
5
GND
GND 32
6
VRRDY
7
VIN
8
BST
9
IOUT 36
IMAX 35
GND
49
TSENSE 34
VBOOT 31
GL 30
SW 29
VIN
50
GH
SW
51
SW 28
SW
PGND
PGND
PGND
PGND
PGND
PGND
SW 25
VIN
12 VIN
VIN
SW 26
VIN
11 VIN
VIN
SW 27
VIN
10 SW
13
14
15
16
17
18
19
20
21
22
23
24
Figure 1. Pin Configuration
(Top View)
VIN
BST
VIN
GH
+5V
PGND
SW
VCCP
SW
VOUT
GL
ILIM
VCC
CSCOMP
GND
EN
VRHOT#
SDIO
ALERT#
SCLK
CSSUM
NCP81251
CSREF
VBOOT
VRRDY
TSENSE
COMP
FB
DIFFOUT
IMAX
FREQ
VSP
IOUT
VSN
Figure 2. Typical Application Circuit
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NCP81251
BST
VCCP
GH
VIN
VIN
VCC
UVLO
SW
Gate Drive
EN
VCCP
GND
PGND
DAC
VRRD
Y
Control Logic
&
Protections
&
VR Ready
VSP−VSN
GL
OCP
PWM
IMON
IOUT
Current Measurement
and Limit
OCP
ILIM
VRH
OT#
VCS
PWM
Control
Thermal
Management
CSREF
TSENSE
CSS
UM
FREQ
VBO
OT
Frequency
&
VBOOT
Detection
VIN
Current
Sense
1.0
TSEN
SE
CSR
EF
DAC
CSCOMP
VDROOP
COMP
VSP−VSN
CSC
OMP
COMP
VBOOT
IMAX
MUX
Error
Amp
IOUT
ADC
IMAX
Vref
TSENSE
FB
1.3V
DIFF
OUT
SDIO
VDROOP
SCLK
SVID Interface
VSP
Differential
Amplifier
Registers
Vref
DAC
ALE
RT#
DAC
DAC
DVID
FeedForward
Figure 3. Functional Block Diagram
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VSN
NCP81251
Table 1. PIN DESCRIPTION
Pin
Name
Type
1
VRHOT#
Logic Output
Description
2
SDIO
Logic Bidirectional
3
ALERT#
Logic Output
4
SCLK
Logic Input
5, 32,
49
GND
Analog Ground
Analog Ground. Ground of internal control circuits. Must be connected to the system
ground.
6
VRRDY
Logic Output
Voltage Regulator Ready. Open−drain output. Provides a logic high valid power good
output signal, indicating the regulator’s output is in regulation window.
7,
11−17,
50
VIN
Power Input
Power Supply Input. These pins are the power supply input pins of the device, which are
connected to drain of internal high−side power MOSFET. 22 mF or more ceramic capacitors
must bypass this input to power ground. The capacitors should be placed as close as
possible to these pins.
8
BST
Power
Bidirectional
Bootstrap. Provides bootstrap voltage for the high−side gate driver. A 0.1 mF ~ 1 mF
ceramic capacitor is required from this pin to SW (pin10). A 1 ~ 2 W resistor may be
employed in series with the BST cap to reduce switching noise and ringing when needed.
9
GH
Analog Output
Gate of High−Side MOSFET. Directly connected with the gate of the high−side power
MOSFET.
10
SW
Power Return
Switching Node. Provides a return path for integrated high−side gate driver. It is internally
connected to source of high−side MOSFET.
18,
25−29,
51
SW
Power Output
Switch Node. Pins to be connected to an external inductor. These pins are interconnection
between internal high−side MOSFET and low−side MOSFET.
19−24
PGND
Power Ground
Power Ground. These pins are the power supply ground pins of the device, which are
connected to source of internal low−side power MOSFET. Must be connected to the system
ground.
30
GL
Analog Output
Gate of Low−Side MOSFET. Directly connected with the gate of the low−side power MOSFET.
31
VBOOT
Analog Input
33
VCCP
Analog Power
34
TSENSE
Analog
35
IMAX
Analog Input
36
IOUT
Analog Output
OUT Current Monitor. Provides output signal representing output current by connecting a
resistor from this pin to ground. Shorting this pin to ground disables IMON function.
37
ILIM
Analog Output
Limit of Current. A resistor from this pin to CSCOMP programs over−current threshold with
inductor current sense.
38
CSCOMP
Analog Output
Current Sense COMP. Output pin of current sense amplifier.
39
CSSUM
Analog Input
Current Sense SUM. Inverting input of current sense amplifier.
40
CSREF
Analog Input
Current Sense Reference. Non−Inverting input of current sense amplifier.
41
FREQ
Analog Input
Frequency. A resistor from this pin to ground programs switching frequency.
42
COMP
Analog
43
FB
Analog Input
44
DIFFOUT
Analog Output
45
VSN
Analog Input
Voltage Sense Negative Input. Inverting input of differential voltage sense amplifier. It is
also used for DVID feed forward function with an external resistor.
46
VSP
Analog Input
Voltage Sense Positive Input. Non−inverting input of differential voltage sense amplifier.
47
VCC
Analog Power
Voltage Supply of Controller. Power supply input pin of control circuits. A 1 mF or larger
ceramic capacitor bypasses this input to ground. This capacitor should be placed as close
as possible to this pin.
48
EN
Logic Input
VR HOT. Logic low output represents over temperature.
Serial Data IO Port. Data port of SVID interface.
ALERT. Open−drain output. Provides a logic low valid alert signal of SVID interface.
Serial Clock. Clock input of SVID interface.
Boot−Up Voltage. A resistor from this pin to ground programs SVID address.
Voltage Supply of Gate Driver. Power supply input pin of internal gate driver. A 4.7 mF or
larger ceramic capacitor bypasses this input to ground. This capacitor should be placed as
close as possible to this pin.
Temperature Sense. An external temperature sense network is connected to this pin.
Current Maximum. A resistor from this pin to ground programs IMAX.
Compensation. Output pin of error amplifier.
Feedback. Inverting input to error amplifier.
Differential Amplifier Output. Output pin of differential voltage sense amplifier.
Enable. Logic high enables the device and logic low makes the device in standby mode.
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NCP81251
Table 2. MAXIMUM RATINGS
Value
Rating
Symbol
Power Supply Voltage to PGND
Min
VVIN
Switch Node to PGND
VSW
Max
Unit
30
V
30
V
VCC, VCCP
−0.3
6.5
V
BST_PGND
−0.3
33
38 (<50 ns)
V
BST to SW
BST_SW
−0.3
6.5
V
GH to SW
GH
−0.3
−2 (<200 ns)
BST+0.3
V
GL to GND
GL
−0.3
−2 (<200 ns)
VCCP+0.3
V
VSN
−0.3
0.3
V
IOUT
IOUT
−0.3
2.5
V
PGND to GND
PGND
−0.3
0.3
V
−0.3
VCC+0.3
V
−100
−10
100
10
Analog Supply Voltage to GND
BST to PGND
VSN to GND
Other Pins
Latch up Current: (Note 1)
All pins, except digital pins
Digital pins
ILU
Operating Junction Temperature Range
TJ
−40
125
°C
Operating Ambient Temperature Range
TA
−40
125
°C
Storage Temperature Range
TSTG
−40
150
°C
Thermal Resistance Junction to Board (Note 2)
RθJB
8.2
°C/W
Thermal Resistance Junction to Ambient (Note 2)
RθJA
21.8
°C/W
PD
4.59
W
MSL
3
−
Power Dissipation at TA = 25°C (Note 3)
Moisture Sensitivity Level (Note 4)
mA
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
1. Latch up Current per JEDEC standard: JESD78 class II.
2. The thermal resistance values are dependent of the internal losses split between devices and the PCB heat dissipation. This data is based
on a typical operation condition with a 4−layer FR−4 PCB board, which has two, 1−ounce copper internal power and ground planes and
2−ounce copper traces on top and bottom layers with approximately 80% copper coverage. No airflow and no heat sink applied (reference
EIA/JEDEC 51.7). It also does not account for other heat sources that may be present on the PCB next to the device in question (such as
inductors, resistors etc.)
3. The maximum power dissipation (PD) is dependent on input voltage, output voltage, output current, external components selected, and PCB
layout. The reference data is obtained based on TJMAX = 125°C and RθJA = 21.8°C/W.
4. Moisture Sensitivity Level (MSL): 3 per IPC/JEDEC standard: J−STD−020D.1.
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NCP81251
Table 3. ELECTRICAL CHARACTERISTICS (VIN = 12 V, VCC = VCCP = 5 V, VOUT = 1.0 V, typical values are referenced to TJ =
25°C, Min and Max values are referenced to TJ from −40°C to 125°C. unless otherwise noted.)
Test Conditions
Characteristics
Symbol
Min
Typ
Max
Unit
SUPPLY VOLTAGE
Supply Voltage VIN Range
(Note 5)
VIN
Supply Voltage VCC Range
(Note 5)
VCC
4.75
5
5.25
V
Supply Voltage VCCP Range
(Note 5)
VCCP
4.75
5
5.25
V
Falling Threshold
VINUV−
3.0
3.25
3.5
V
Hysteresis
VINHYS
650
−
mV
Falling Threshold
VCCUV−
3.8
4.08
−
V
Rising Threshold
VCCUV+
−
4.34
4.5
V
Hysteresis
VCCHYS
−
260
−
mV
12
V
SUPPLY VOLTAGE MONITOR
VIN UVLO
VCC UVLO
SUPPLY CURRENT
VIN Quiescent Supply Current
(Power MOSFETs)
EN high, no load, PS0,1,2 Modes
EN high, no load, PS3 Mode
EN high, PS4 Mode (Note 6)
IQ
−
−
−
1.5
1.5
−
3
3
1
mA
mA
mA
VIN Shutdown Current
EN low (Note 6)
ISD
−
−
1
mA
VCC Quiescent Supply Current
(Controller)
EN high, no load, PS0,1,2 Modes
EN high, no load, PS3 Mode
EN high, PS4 Mode (Note 6)
IQCC
−
−
−
8.0
7.5
170
12
12
194
mA
mA
mA
VCC Shutdown Current
EN low (Note 6)
ISDCC
−
−
100
mA
VCCP Quiescent Supply Current
(Gate Driver)
EN high, no load, PS0,1,2 Modes
EN high, no load, PS3 Mode
EN high, PS4 Mode
IQCCP
−
−
−
0.7
0.7
−
1.25
1.25
2
mA
mA
mA
VCCP Shutdown Current
EN low
ISDCCP
−
−
2
mA
(Note 5)
VOUT
0
−
2.3
V
+8
+10
+0.9
mV
mV
%
OUTPUT VOLTAGE
Output Voltage Range
REGULATION ACCURACY
System Voltage Accuracy
0.25 V < DAC < 0.8 V
0.8 V < DAC < 1.0 V
1.0 V < DAC < 1.52 V
−8
−10
−0.9
DVID
Fast Slew Rate
Default
Soft Start Slew Rate
Slow Slew Rate
FSR
14
mV/ms
SSSR
FSR/4
mV/ms
SSR
FSR/2
FSR/4
(default)
FSR/8
FSR/16
mV/ms
GAIN_DVA
1.0
V/V
BW_DVA
10
MHz
DIFFERENTIAL VOLTAGE−SENSE AMPLIFIER
DC Gain
VSP−VSN = 0.5 V to 2.3 V
−3 dB Gain Bandwidth
CL = 20 pF to GND, RL = 10 kW to
GND (Note 5)
VSP Input Voltage Range
(Note 5)
VSP
−0.3
−
3.0
V
VSN Input Voltage Range
(Note 5)
VSN
−0.3
−
0.3
V
Input Bias Current
VSP,CSREF = 1.3 V
IVSP
IVSN
−15
−100
15
100
mA
nA
5. Guaranteed by design, not tested in production.
6. TJ = 25°C.
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NCP81251
Table 3. ELECTRICAL CHARACTERISTICS (VIN = 12 V, VCC = VCCP = 5 V, VOUT = 1.0 V, typical values are referenced to TJ =
25°C, Min and Max values are referenced to TJ from −40°C to 125°C. unless otherwise noted.)
Characteristics
Test Conditions
Symbol
Min
Typ
Max
Unit
DIFFERENTIAL CURRENT−SENSE AMPLIFIER
DC Gain
(Note 5)
−3dB Gain Bandwidth
CL = 20 pF to GND, RL = 10 kW to
GND (Note 5)
Input Offset Voltage
Input Bias Current
CSSUM = CSREF = 1.2 V
GAIN_DCA
80
dB
BW_DCA
10
MHz
VOS_CS
−300
ICSSUM
ICSREF
−7.5
−10
−
300
mV
7.5
10
nA
mA
ERROR AMPLIFIER
DC Gain
CL = 20 pF to GND, RL = 10 kW to
GND (Note 5)
GAIN_EA
80
dB
Unity Gain Bandwidth
CL = 20 pF to GND, RL = 10 kW to
GND (Note 5)
BW_EA
20
MHz
Slew Rate
nVin = 100 mV, G = −10 V/V,
nVout = 1.5 V – 2.5 V,
CL = 20 pF to GND, RL = 10 kW to
GND (Note 5)
SR_EA
25
V/ms
Output Voltage Swing
Isource_EA = 2 mA
Vmax_EA
3.5
−
−
Isink_EA = 2 mA
Vmin_EA
−
−
1
FB Voltage
VFB
1.3
V
V
IFB
−1.5
1.5
mA
FSW
500
1200
kHz
VFREQ
1.95
2.0
2.05
V
ENABLE Input High Voltage
VEN_H
0.8
−
−
V
ENABLE Input Low Voltage
VEN_L
−
−
0.3
V
ENABLE Input Hysteresis
VEN_HYS
−
300
−
mV
ENABLE Input Bias Current
IEN_BIAS
−
1.0
mA
Input Bias Current
VFB = 1.3 V
SWITCHING FREQUENCY
Normal Operation Frequency
(Programmed by a resistor at FREQ
pin)
(Note 5)
FREQ Output Voltage
CONTROL LOGIC
TSENSE
Alert# Assert Threshold
491
mV
Alert# De−assert Threshold
513
mV
VR_HOT# Assert Threshold
472
mV
VR_HOT# De−assert Threshold
494
mV
TSENSE Bias Current
VTSENSE = 0.4 V
112
120
128
mA
VBOOT
Sensing Current
VVBOOT = GND
10
mA
VIMAX = GND
10
mA
IMAX
Sensing Current
5. Guaranteed by design, not tested in production.
6. TJ = 25°C.
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NCP81251
Table 3. ELECTRICAL CHARACTERISTICS (VIN = 12 V, VCC = VCCP = 5 V, VOUT = 1.0 V, typical values are referenced to TJ =
25°C, Min and Max values are referenced to TJ from −40°C to 125°C. unless otherwise noted.)
Characteristics
Test Conditions
Symbol
Min
Typ
Max
Unit
ADC
Voltage Range
0
2.0
V
Total Unadjusted Error (TUE)
−1
1
%
1
LSB
Differential Nonlinearity (DNL)
8−bit
Power Supply Sensitivity
±1
%
Conversion Time
30
ms
Round Robin
90
ms
VR_READY (VRRDY Output)
Rise Time
External 1 kW pull−up to 3.3 V,
CTOT = 45 pF, DVo = 10% to 90%
120
ns
Fall Time
External 1 kW pull−up to 3.3 V,
CTOT = 45 pF, DVo = 90% to 10%
20
ns
Output Voltage at Power−Up
Pulled up to 5 V via 2 kW
VR_READY Delay (Rising)
DAC = Target to VR_READY
50
ms
VR_READY Delay (Falling)
From OCP or OVP
5
ms
VRRDY Pin Low Voltage
Voltage at VRRDY pin with 4 mA sink
current
VPG_L
−
−
0.3
V
VRRDY Pin Leakage Current
VRRDY = 5 V
PG_LK
−1.0
−
1.0
mA
2.8
2.9
3.0
V
350
400
425
mV
−
−
1.0
V
OVER VOLTAGE PROTECTION
Absolute Over Voltage Threshold
During Soft−Start
Over Voltage Threshold Above DAC
VSP rising
Over Voltage Delay
VSP rising to GH low
50
ns
UNDER VOLTAGE PROTECTION
Under Voltage Threshold Below DAC
VSP falling
250
Under−voltage Delay
300
350
mV
ms
5
OVER CURRENT PROTECTION
ILIM Threshold Current
(OCP shutdown after 50 ms delay)
ILIMTH_SLOW
ILIM Threshold Current
(immediate OCP shutdown)
ILIMTH_FAST
mA
8.5
10.0
12.0
12.0
15.0
18.0
mA
IOUT OUTPUT
Current Gain
(IOUTCURRENT) / (ILIMCURRENT);
RILIM = 20 kW; RIOUT = 5.0 kW;
DAC = 0.8 V, 1.25 V, 1.52 V
9.5
10
10.5
A/A
Input Referred Offset Voltage
ILIM − CSREF
−5.5
−
5.5
mV
Output Source Current
ILIM sink current = 80 mA
mA
800
HIGH−SIDE MOSFET
Drain−to−Source ON Resistance
VGS = 4.5 V, ID = 10 A
RON_H
−
8.0
−
mW
VGS = 4.5 V, ID = 10 A
RON_L
−
4.0
−
mW
LOW−SIDE MOSFET
Drain−to−Source ON Resistance
5. Guaranteed by design, not tested in production.
6. TJ = 25°C.
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NCP81251
Table 3. ELECTRICAL CHARACTERISTICS (VIN = 12 V, VCC = VCCP = 5 V, VOUT = 1.0 V, typical values are referenced to TJ =
25°C, Min and Max values are referenced to TJ from −40°C to 125°C. unless otherwise noted.)
Characteristics
Test Conditions
Symbol
Min
Typ
Max
Unit
HIGH−SIDE GATE DRIVE
Pull−High Drive ON Resistance
VBST – VSW = 5 V
RDRV_HH
−
1.2
2.9
W
Pull−Low Drive ON Resistance
VBST – VSW = 5 V
RDRV_HL
−
0.8
2.2
W
GH Propagation Delay Time
From GL falling to GH rising
TGH_d
15
ns
LOW−SIDE GATE DRIVE
Pull−High Drive ON Resistance
VCCP – VPGND = 5 V
RDRV_LH
−
0.9
3.0
W
Pull−Low Drive ON Resistance
VCCP – VPGND = 5 V
RDRV_LL
−
0.4
1.25
W
GL Propagation Delay Time
From GH falling to GL rising
TGL_d
(Note 5)
RSW
−
1.88
−
kW
Ron_BST
5
13
22
W
10
ns
SW to PGND RESISTANCE
SW to PGND Pull−Down Resistance
BOOTSTRAP RECTIFIER SWITCH
On Resistance
EN = L or EN = H and DRVL = H
5. Guaranteed by design, not tested in production.
6. TJ = 25°C.
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
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NCP81251
TGL_f
TGL_r
GL
TGH_d
GH to SW
TGH_f
TGH_r
VTH
VTH
SW
NOTE:
TGL_d
1.0 V
Timing is referenced to the 90% and 10% points, unless otherwise noted.
Figure 4. Timing Diagram of Gate Drivers
Table 4. STATE TRUTH TABLE
STATE
VR_RDY Pin
Error AMP Comp Pin
OVP & UVP
POR
0 < VCC < UVLO
N/A
N/A
N/A
Disabled
EN < threshold
UVLO > threshold
Low
Low
Disabled
Start up Delay & Calibration
EN > threshold
UVLO > threshold
Low
Low
Disabled
Soft Start
EN > threshold
UVLO > threshold
Low
Operational
Active / No latch
Normal Operation
EN > threshold
UVLO > threshold
High
Operational
Active / Latching
Over Voltage
Low
N/A
DAC + 400 mV
Over Current
Low
Operational
Last DAC Code
Vout = 0 V
Low: if Reg34h:bit0 = 0;
High:if Reg34h:bit0 = 1
Clamped at 0.9 V
Disabled
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Method of Reset
N/A
NCP81251
DETAILED DESCRIPTION
General
mode, the inductor current is continuous and the device
operates in quasi−fixed switching frequency in medium and
heavy load range, while the inductor current becomes
discontinuous and the device automatically operates in PFM
mode with an adaptive fixed on time and variable switching
frequency in light load range.
The NCP81251, a single−phase synchronous buck
regulator, integrates power MOSFETs to provide a
high−efficiency and compact−footprint power management
solution for new generation computing CPUs. The device is
able to deliver up to 14 A TDC output current on an
adjustable output with SVID interface. Operating in high
switching frequency up to 1.2 MHz allows employing small
size inductors and capacitors while maintaining high
efficiency due to integrated solution with high performance
power MOSFETs. Current−mode RPM control with
feedforward from both input power supply and output
voltage ensures stable operation over wide operation
condition.
Serial VID interface (SVID)
Current−Mode RPM Operation
Boot Voltage and SVID Address
The NCP81251 operates with the current−mode
Ramp−Pulse−Modulation (RPM) scheme in PS0/1/2/3
operation modes. In forced CCM mode, the inductor current
is always continuous and the device operates in quasi−fixed
switching frequency, which has a typical value programmed
by users through a resistor at pin FREQ. In auto CCM/DCM
Table 5 shows two boot voltage options of 1.0 V and 1.1 V
programmed by an external 1% resistor Rvboot from Vboot
pin to GND, which programs SVID address as well. Both
Vboot voltage and SVID address are set on power up and
cannot be changed after the initial power up sequence is
complete.
The NCP81251 supports Intel serial VID interface. It
communicates with the microprocessor through three wires
(SCLK, SDIO, ALERT#). For NCP81251, VID code
change rate is controlled by the SVID interface with three
options. Information regarding SVID interface can be
obtained from Intel.
Table 5. BOOT VOLTAGE AND SVID ADDRESS CONFIGURATION
Vboot Pin Voltage (mV)
Rvboot
(W)
Min
Typ
Max
Address
Vboot
(V)
0
0
0
102
0x0
1.0
14.0k
102
140
180
0x1
1.0
22.1k
180
219
258
0x2
1.0
30.1k
258
301
344
0x3
1.0
39.2k
344
391
438
0x4
1.0
48.7k
438
484
531
0x5
1.0
57.6k
531
578
625
0x6
1.0
68.1k
625
676
727
0x7
1.0
78.7k
727
781
836
0x8
1.0
88.7k
836
894
953
0x0
1.1
100k
953
1007
1062
0x1
1.1
113k
1062
1125
1188
0x2
1.1
124k
1188
1250
1312
0x3
1.1
137k
1312
1378
1445
0x4
1.1
150k
1445
1511
1578
0x5
1.1
165k
1578
1648
1719
0x6
1.1
178k
1719
1789
1859
0x7
1.1
196k
1859
1950
−
0x8
1.1
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11
NCP81251
Switching Frequency
Switching frequency is programmed by a resistor RFREQ
to ground at the FREQ pin. The typical frequency range is
from 500 kHz to 1.2 MHz. The FREQ pin provides
approximately 2 V out and the source current is mirrored
into the internal ramp generator. The switching frequency
can be found in Figure 5 with a given RFREQ. The frequency
shown in Figure 5 is under condition of 10 A output current
at VID = 1 V. The frequency has a variation over VID
voltage and loading current, which maintains similar output
ripple voltage over different operation condition. Figure 6
shows frequency variations over the VID voltage range.
Figure 5. Switching Frequency vs. RFREQ
Figure 6. Switching Frequency vs. VID Voltage
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12
NCP81251
Remote Voltage Sense
The VDROOP voltage is a half of the voltage difference
between the CSCOMP pin and the CSREF pin.
A high performance differential amplifier is provided to
accurately sense the output voltage of the regulator. The
VSP and VSN inputs should be connected to the regulator’s
output voltage sense points. The output (DIFOUT) of the
remote sense amplifier is a sum of the error voltage (between
the output VSP−VSN and the DAC), a load−line voltage
VDROOP, and a 1.3 V DC bias.
V DROOP + V CS + V CSREF * V CSCOMP
The DIFOUT signal then goes through a compensation
network and into the inverting input (FB pin) of an error
amplifier. The non−inverting input of the error amplifier is
connected to the same 1.3 V used for the differential sense
amplifier output bias.
V DIFOUT + ǒV VSP * V VSNǓ ) ǒ1.3 V * V DACǓ ) V_DROOP
(eq. 1)
IOUT
36
RIOUT
Vcs
1
ILIM
37
RILIM
VDROOP
35
RICCMAX
ICCMAX
ICCMAX
&
IOUT
&
ILIM
SW
L
CSREF
VOUT
Rcs_NTC
IOUT
Ccs1
Ccs2
Rcs2
Current
Sense
DCR
38
Rcs1
CSCOMP
CSSUM
(eq. 2)
Rcs3
39
40
Figure 7. Differential Current−Sense Circuit Diagram
Differential Current Sense
The values of Rcs1 and Rcs2 are set based on a 220k NTC
thermistor and the temperature effect of the inductor and
thus usually they should not need to be changed. The gain
Gcs can be adjusted by the value change of the Rcs3 resistor.
The internal Vcs voltage should be set to the output voltage
droop in applications with a DC load line requirement.
In order to recover the inductor DCR voltage drop current
signal, the pole frequency in the CSCOMP filter should be
set equal to the zero from the output inductor, that means
The differential current−sense circuit diagram is shown in
Figure 7. An internally−used voltage signal Vcs,
representing the inductor current level, is the voltage
difference between CSREF and CSCOMP. The output side
of the inductor is used to create a low impedance virtual
ground. The current−sense amplifier actively filters and
gains up the voltage applied across the inductor to recover
the voltage drop across the inductor’s DC resistance (DCR).
RCS_NTC is placed close to the inductor to sense the
temperature. This allows the filter time constant and gain to
be a function of the Rth_NTC resistor and compensate for
the change in the DCR with temperature. The DC gain in the
current sensing loop is
G CS +
V CS
V DCR
+
V CSREF * V CSCOMP
I OUT @ DCR
+
R CS
R CS3
C CS1 ) C CS2 +
R CS + R CS2 )
(eq. 3)
LL +
R CS1 ) R CS_NTC
(eq. 5)
Ccs1 and Ccs2 are in parallel to allow for a fine tuning of
the time constant using commonly available values. In
applications with a droop voltage VDROOP, the DC load line
LL can be obtained by
Where
R CS1 @ R CS_NTC
L
DCR @ R CS
(eq. 4)
+
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13
V DROOP
I OUT
R CS
R CS3
+
ǒVCSREF * VCSCOMPǓ
@ DCR
I OUT
(eq. 6)
NCP81251
Over Current Protection
ground such that a load equal to ICCMAX generates a 2 V
signal on IOUT. A pull−up resistor to 5 V VCC can be used
to offset the IOUT signal positive if needed.
The NCP81251 provides two different types of current
limit protection. Current limits are programmed with a
resistor RILIM between the CSCOMP pin and the ILIM pin.
The current from the ILIM pin to this resistor is then
compared to two internal currents (10 mA and 15 mA)
corresponding to two different current limit thresholds ILIM
and ILIM_Fast (150% of ILIM level). If the ILIM pin
current exceeds the 10 mA level, an internal latch−off timer
starts. The controller shuts down if the fault is not removed
after 50 ms. If the current into the pin exceeds 15 mA the
controller will shut down immediately. To recover from an
OCP fault the EN pin must be cycled low.
The value of RILIM can be designed using the following
equation with a required over current protection threshold
ILIM and a known current−sense network.
R ILIM +
+
V CS@I LIM
R CS
R CS3
10 m
@
ǒ
+
I LIM )
R CS
R CS3
R IOUT +
2 @ L @ F SW @ V IN
Ǔ
@ R ILIM
1
+
5@
RCS
RCS3
@ R ILIM
(eq. 9)
@ ICC_MAX @ DCR
Input UVLO Protection
NCP81251 monitors supply voltages at the VCC pin and
the VIN pins in order to provide under voltage protection. If
either supply drops below its threshold, the controller will
shut down the outputs. Upon recovery of the supplies, the
controller reenters its startup sequence, and soft start begins.
Output Under−Voltage Protection
@ I LIM_PK @ DCR @ 10 5
ǒVIN * VOUTǓ @ VOUT
2
10 @ V CS@ICC_MAX
The output voltage is monitored by a dedicated
differential amplifier. If the output falls below target by
more than “Under Voltage Threshold below DAC−Droop”,
the UVL comparator sends the VR_RDY signal low.
(eq. 7)
@ DCR @ 10 5
Output Over−Voltage Protection
ICC_MAX
During normal operation the output voltage is monitored
at the differential inputs VSP and VSN. If the output voltage
exceeds the DAC voltage by “Over Voltage Threshold above
DAC”, GH will be forced low, and GL will go high. After the
OVP trips, the DAC ramps slowly down to zero to avoid a
negative output voltage spike during shutdown. If the
DAC+OVP Threshold drops below the output, GL will
again go high, and will toggle between low and high as the
output voltage follows the DAC+OVP Threshold down.
When the DAC gets to zero, the GH will be held low and the
GL will remain high. To reset the part, the EN pin must be
cycled low. During soft−start, the OVP threshold is set to
2.9 V. This allows the controller to start up without false
triggering the OVP.
A resistor connected from IMAX pin to ground sets
ICC_MAX value at startup. A 10 mA current is sourced from
this pin to generate a voltage on the program resistor. The
resistor value can be determined by the following equation.
The resistor value should be no less than 10 k.
ICC_MAX +
R ICCMAX @ 10 m @ 64
2
+ R ICCMAX @ 3.2 @ 10 −4
(eq. 8)
IOUT
The IOUT pin sources a current equal to the ILIM sink
current gained by the IOUT Current Gain (10 typ.). The
voltage of the IOUT pin is monitored by the internal A/D
converter and should be scaled with an external resistor to
(b) During Start Up
(a) Normal Operation Mode
Figure 8. Function of Over Voltage Protection
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14
NCP81251
Temperature Sense and Thermal Alert
monitors the voltage at the TSENSE pin and compares the
voltage to internal thresholds and assert ALERT# or
VRHOT# once it trips the thresholds. The DC voltage at
TSENSE pin can be calculated by
The NCP81251 provides an external temperature sense
and a thermal alert in normal operation mode. The
temperature sense and thermal alert circuit diagram is shown
in Figure 9. A precision current ITSENSE is sourced out the
output of the TSENSE pin to generate a voltage across the
temperature sense network, which consists of a NTC
thermistor R_NTC (100 kW typ.), two resistors R_COMP1
(0 W typ.) and R_COMP2 (8.2 kW typ.), and a filter
capacitor C_Filter (0.1 mF typ.). The voltage on the
temperature sense input is sampled by the internal A/D
converter and then digitally converted to temperature and
stored in SVID register 17h. Usually the thermistor is placed
close to a hot spot like inductor or NCP81251 itself. A 100k
NTC
thermistor
similar
to
the
Murata
NCP15WF104D03RC should be used. The NCP81251 also
ǒ
R COMP1 )
ǒ ǒ ǓǓ
R NTC_T + R NTC_T @ exp B @
0
where RNTC_T0 is a known resistance of R_NTC at an
absolute temperature T0, and B is the B−constant of R_NTC.
TSENSE
VRHOT#
R_COMP2
C_Filter
3.3V
ALERT#
3
1
1
*
T T0
(eq. 11)
R_NTC
1
Ǔ
R COMP2 ) R NTC_T
RNTC_T is the resistance of R_NTC at an absolute
temperature T, which is obtained by
Thermal
Management
VRHOT#
R COMP2 @ R NTC_T
(eq. 10)
R_COMP1
34
V TSENSE + I TSENSE @
ALERT#
Figure 9. Temperature Sense and Thermal Alert Circuit Diagram
www.onsemi.com
15
NCP81251
LAYOUT GUIDELINES
Electrical Layout Considerations
limiting, and IOUT reporting. The filter cap from
CSCOMP to CSREF should be close to the controller.
The temperature compensating thermistor should be
placed as close as possible to the inductor. The wiring
path should be kept as short as possible and well away
from the switch node.
− Compensation Network: The small feedback cap from
COMP to FB should be as close to the controller as
possible. Keep the FB traces short to minimize their
capacitance to ground.
− SVID Bus: The Serial VID bus is a high speed data bus
and the bus routing should be done to limit noise
coupling from the switching node. The signals should
be routed with the Alert# line in between the SVID
clock and SVID data lines. The SVID lines must be
ground referenced and each line’s width and spacing
should be such that they have nominal 50 W impedance
with the board stackup.
Good electrical layout is a key to make sure proper
operation, high efficiency, and noise reduction. Electrical
layout guidelines are:
− Power Paths: Use wide and short traces for power
paths (such as VIN, VOUT, SW, and PGND) to reduce
parasitic inductance and high−frequency loop area. It is
also good for efficiency improvement.
− Power Supply Decoupling: The device should be well
decoupled by input capacitors and input loop area
should be as small as possible to reduce parasitic
inductance, input voltage spike, and noise emission.
Usually, a small low−ESL MLCC is placed very close
to VIN and PGND pins.
− VCC Decoupling: Place decoupling caps as close as
possible to the controller VCC and VCCP pins. The
filter resistor at VCC pin should be not higher than
2.2 W to prevent large voltage drop.
− Switching Node: SW node should be a copper pour,
but compact because it is also a noise source.
− Bootstrap: The bootstrap cap and an option resistor
need to be very close and directly connected between
pin 8 (BST) and pin 10 (SW). No need to externally
connect pin 10 to SW node because it has been
internally connected to other SW pins.
− Ground: It would be good to have separated ground
planes for PGND and GND and connect the two planes
at one point. Directly connect GND pin to the exposed
pad and then connect to GND ground plane through
vias.
− Voltage Sense: Use Kelvin sense pair and arrange a
“quiet” path for the differential output voltage sense.
− Current Sense: Careful layout for current sensing is
critical for jitter minimization, accurate current
Thermal Layout Considerations
Good thermal layout helps high power dissipation from a
small package with reduced temperature rise. Thermal
layout guidelines are:
− The exposed pads must be well soldered on the board.
− A four or more layers PCB board with solid ground
planes is preferred for better heat dissipation.
− More free vias are welcome to be around IC and
underneath the exposed pads to connect the inner
ground layers to reduce thermal impedance.
− Use large area copper pour to help thermal conduction
and radiation.
− Do not put the inductor to be too close to the IC, thus
the heat sources are distributed.
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16
NCP81251
PACKAGE DIMENSIONS
QFN48 6x6, 0.4P
CASE 485CJ
ISSUE A
ÉÉÉÉ
ÉÉÉÉ
ÉÉÉÉ
ÉÉÉÉ
ÉÉ
ÉÉ
EXPOSED Cu
A B
D
PIN ONE
REFERENCE
2X
0.15 C
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994.
2. CONTROLLING DIMENSIONS: MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED TERMINAL AND IS
MEASURED BETWEEN 0.15 AND 0.30mm FROM TERMINAL TIP
4. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS
THE TERMINALS.
5. POSITIONAL TOLERANCE APPLIES TO ALL THREE EXPOSED
PADS IN BOTH X AND Y AXIS.
DETAIL B
ALTERNATE
CONSTRUCTION
E
L
L
L1
0.15 C
2X
MOLD CMPD
DETAIL A
TOP VIEW
ALTERNATE TERMINAL
CONSTRUCTIONS
(A3)
DETAIL B
A
0.10 C
L2
0.08 C
A1
NOTE 4
45 5
SEATING
PLANE
C
SIDE VIEW
DETAIL C
D2
D3
DETAIL A
D4
G3
DETAIL C
13
G4
13
25
E3
25
E2
1
48
48X
H4
E4
L
0.10
37
e
e/2
BOTTOM VIEW
H3
NOTE 5
48X
b
0.10
0.05
H2
1
C A B
M
48
D5
C A B
M
C
M
37
SUPPLEMENTAL
BOTTOM VIEW
NOTE 3
RECOMMENDED
SOLDERING FOOTPRINT*
48X
6.30
0.58
4.81
48X
0.25
2.09
4.80 6.30
0.40
PITCH
2.54
1.91
2.66
DIMENSIONS: MILLIMETERS
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
www.onsemi.com
17
DIM
A
A1
A3
b
D
D2
D3
D4
D5
E
E2
E3
E4
e
G3
G4
H2
H3
H4
L
L1
L2
MILLIMETERS
MIN
MAX
0.80
1.00
−−−
0.05
0.20 REF
0.15
0.25
6.00 BSC
4.53
4.73
1.64
1.84
2.42
2.62
4.58
4.78
6.00 BSC
1.86
2.06
2.41
2.61
2.30
2.50
0.40 BSC
1.45 BSC
1.06 BSC
1.40 BSC
1.19 BSC
1.10 BSC
0.25
0.45
−−−
0.15
0.15 REF
NCP81251
Intel is a registered trademark of Intel Corporation in the U.S. and/or other countries.
ON Semiconductor and the
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries.
SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed
at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation
or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and
specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets
and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each
customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended,
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expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim
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NCP81251/D