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LMP8640, LMP8640-Q1, LMP8640HV
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
LMP8640/-Q1/HV Precision High Voltage Current Sense Amplifiers
1 Features
3 Description
•
•
The LMP8640, LMP8640-Q1 and the LMP8640HV
are precision current sense amplifiers that detect
small differential voltages across a sense resistor in
the presence of high input common mode voltages
with a supply voltage range from 2.7 V to 12 V.
1
•
•
•
•
•
•
•
•
•
Typical Values, TA = 25°C
High Common-Mode Voltage Range
– LMP8640: -2 V to 42 V
– LMP8640-Q1: -2 V to 42 V, AEC-Q100
– LMP8640HV: -2 V to 76 V
Supply Voltage Range: 2.7 V to 12 V
Gain Options: 20 V/V; 50 V/V; 100 V/V
Max Gain Error: 0.25%
Low Offset Voltage: 900 µV
Input Bias Current: 13 µA
PSRR: 85 dB
CMRR (2.1V to 42V): 103 dB
Temperature Range: -40°C to 125°C
6-Pin Thin SOT-23 Package
The LMP8640 and LMP8640-Q1 accept input signals
with common mode voltage range from -2 V to 42 V,
while the LMP8640HV accepts input signal with
common mode voltage range from -2 V to 76 V. The
LMP8640 and LMP8640HV have fixed gain for
applications that demand accuracy over temperature.
The LMP8640 and LMP8640HV come out with three
different fixed gains 20 V/V, 50 V/V, 100 V/V ensuring
a gain accuracy as low as 0.25%. The output is
buffered in order to provide low output impedance.
This high side current sense amplifier is ideal for
sensing and monitoring currents in DC or battery
powered
systems,
excellent
AC
and
DC
specifications over temperature, and keeps errors in
the current sense loop to a minimum. The LMP8640
and LMP8640HV are ideal choice for industrial and
consumer applications, while the LMP8640-Q1 is an
AEC-Q100 grade 1 qualified version of the LMP8640
for automotive applications. The LMP8640-x is
available in SOT-23-6 package.
2 Applications
•
•
•
•
•
•
High-Side Current Sense
Vehicle Current Measurement
Motor Controls
Battery Monitoring
Remote Sensing
Power Management
Device Information (1)
PART NUMBER
PACKAGE
BODY SIZE (NOM)
LMP8640
LMP8640-Q1
SOT23 (6)
2.9 mm x 1.6 mm
LMP8640HV
(1)
Simplified Schematic
For all available packages, see the orderable addendum at
the end of the datasheet.
Output Voltage vs Input Voltage
IS
-IN
RIN
+
L
o
a
d
LMP8640
RIN
VOUT (V)
+
RS
+IN
+
V
+
VA
G
ADC
VOUT
RG = 2*RIN
V
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
VS =12V, VCM =12V
GAIN 100V/V
GAIN 50V/V
GAIN 20V/V
100
200
300
400
500
600
VSENSE (mV)
-
G = 10 V/V in 20 V/V gain option
G = 25 V/V in 50 V/V gain option
G = 50 V/V in 100 V/V gain option
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LMP8640, LMP8640-Q1, LMP8640HV
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Comparison Table.....................................
Pin Configuration and Functions .........................
Specifications.........................................................
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
8
1
1
1
2
3
3
4
Absolute Maximum Ratings ...................................... 4
Handling Ratings - LMP8640, LMP8640HV.............. 4
Handling Ratings - LMP8640-Q1 .............................. 4
Recommended Operating Conditions (2) ................... 4
Thermal Information .................................................. 5
Electrical Characteristics 2.7 V ................................ 5
Electrical Characteristics 5 V (5)................................ 6
Electrical Characteristics 12 V (5).............................. 8
Typical Characteristics ............................................ 10
Detailed Description ............................................ 14
8.1 Overview ................................................................. 14
8.2 Functional Block Diagram ....................................... 14
8.3 Feature Description................................................. 14
8.4 Device Functional Modes........................................ 17
9
Application and Implementation ........................ 18
9.1 Application Information............................................ 18
9.2 Typical Application .................................................. 18
9.3 Do's and Don'ts ...................................................... 20
10 Power Supply Recommendations ..................... 20
11 Layout................................................................... 20
11.1 Layout Guidelines ................................................. 20
11.2 Layout Example .................................................... 21
12 Device and Documentation Support ................. 23
12.1
12.2
12.3
12.4
12.5
12.6
Device Support......................................................
Documentation Support ........................................
Related Links ........................................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
23
23
23
23
23
23
13 Mechanical, Packaging, and Orderable
Information ........................................................... 23
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision F (April 2013) to Revision G
Page
•
New Q Device added to datasheet ........................................................................................................................................ 1
•
Changed data sheet flow and layout to conform with new TI standards. Added the following sections: Application
and Implementation; Power Supply Recommendations; Layout; Device and Documentation Support; Mechanical,
Packaging, and Ordering Information .................................................................................................................................... 1
2
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Copyright © 2010–2014, Texas Instruments Incorporated
Product Folder Links: LMP8640 LMP8640-Q1 LMP8640HV
LMP8640, LMP8640-Q1, LMP8640HV
www.ti.com
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
5 Device Comparison Table
DEVICE NAME
GAIN
LMP8640-T
x20
QUALIFICATIONS
MAX COMMON MODE
VOLTAGE
-2 V to +42 V
LMP8640-T
x20
LMP8640-Q1-T
x20
-2 V to +42 V
LMP8640-F
x50
-2 V to +42 V
LMP8640-H
x100
-2 V to +42 V
LMP8640HV-T
x20
-2 V to +76 V
LMP8640HV-F
x50
-2 V to +76 V
LMP8640HV-H
x100
-2 V to +76 V
Automotive AEC-Q100, Grade 1
-2 V to +42 V
6 Pin Configuration and Functions
6-Pin SOT-23
DDC0006A Package
(Top View)
VOUT
V
-
+IN
1
LMP8640
LMP8640HV
2
3
+
6
V
5
NC
4
-IN
Pin Functions
PIN
DESCRIPTION
NUMBER
NAME
1
VOUT
2
V-
3
+IN
Positive Input
4
-IN
Negative Input
5
NC
Not Internally Connected
6
V+
Positive Supply Voltage
Copyright © 2010–2014, Texas Instruments Incorporated
Output
Negative Supply Voltage
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Product Folder Links: LMP8640 LMP8640-Q1 LMP8640HV
3
LMP8640, LMP8640-Q1, LMP8640HV
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
www.ti.com
7 Specifications
7.1 Absolute Maximum Ratings (1) (2) (3)
LMP8640 limits also apply to the LMP8640-Q1.
Supply Voltage (VS = V+ - V−)
Differential Voltage +IN- (-IN)
Voltage at pins +IN, -IN
(1)
(2)
(3)
(4)
MAX
UNIT
-0.3
13.2
V
-6
6
V
LMP8640HV
-6
80
V
LMP8640, LMP8640-Q1
-6
60
V
-
+
Voltage at VOUT pin
Junction Temperature
MIN
(4)
V
V
V
-40
150
°C
“Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of
device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or
other conditions beyond those indicated in the Operating Ratings is not implied. Operating Ratings indicate conditions at which the
device is functional and the device should not be operated beyond such conditions.
For soldering specifications,see product folder at www.ti.com and http://www.ti.com/lit/SNOA549.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJ(MAX), θJA, and the ambient temperature,
TA. The maximum allowable power dissipation PDMAX = (TJ(MAX) - TA)/ θJA or the number given in Absolute Maximum Ratings, whichever
is lower.
7.2 Handling Ratings - LMP8640, LMP8640HV
MIN
Tstg
Storage temperature range
Human body model (HBM (1))
V(ESD)
Electrostatic discharge
Charged device model (CDM)
Machine model (MM)
(1)
(2)
(3)
(2)
MAX
UNIT
°C
-65
150
For input pins +IN, -IN
-5000
5000
For all other pins
-2000
2000
All pins
-1250
1250
-200
200
(3)
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)
7.3 Handling Ratings - LMP8640-Q1
Tstg
MIN
MAX
UNIT
-65
150
°C
Human body model (HBM), per AEC Q100-002 (1)
-2000
2000
Charged device model (CDM), per
AEC Q100-011
All pins
-1000
1000
All pins
-200
200
Storage temperature range
V(ESD)
Electrostatic discharge
Machine model (MM)
(1)
(2)
(2)
V
AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC)
7.4 Recommended Operating Conditions (1)
MIN
+
−
Supply Voltage (VS = V - V )
Operating Junction Temperature Range
(1)
(2)
4
(2)
MAX
UNIT
2.7
12
V
-40
125
°C
“Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of
device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or
other conditions beyond those indicated in the Operating Ratings is not implied. Operating Ratings indicate conditions at which the
device is functional and the device should not be operated beyond such conditions.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJ(MAX), θJA, and the ambient temperature,
TA. The maximum allowable power dissipation PDMAX = (TJ(MAX) - TA)/ θJA or the number given in Absolute Maximum Ratings, whichever
is lower.
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Copyright © 2010–2014, Texas Instruments Incorporated
Product Folder Links: LMP8640 LMP8640-Q1 LMP8640HV
LMP8640, LMP8640-Q1, LMP8640HV
www.ti.com
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
7.5 Thermal Information
LMP8640
LMP8640HV
LMP8640-Q1
THERMAL METRIC (1)
UNIT
THIN SOT-23
6 PINS
(2)
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
Junction-to-case (top) thermal resistance
RθJB
Junction-to-board thermal resistance
24.6
ψJT
Junction-to-top characterization parameter
0.3
ψJB
Junction-to-board characterization parameter
23.8
(1)
(2)
165
28
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJ(MAX), θJA, and the ambient temperature,
TA. The maximum allowable power dissipation PDMAX = (TJ(MAX) - TA)/ θJA or the number given in Absolute Maximum Ratings, whichever
is lower.
7.6 Electrical Characteristics 2.7 V
(1)
Unless otherwise specified, all limits ensured for at TA = 25°C, VS= V+ – V-, VSENSE= +IN-(-IN), V+ = 2.7 V, V− = 0 V, −2 V <
VCM < 76 V, RL = 10 MΩ. LMP8640 limits also apply to the LMP8640-Q1.
PARAMETER
MIN (2)
TEST CONDITIONS
VCM = 2.1 V
VOS
Input Offset Voltage
TCVOS
Input Offset Voltage Drift (4)
IB
Input Bias Current
eni
Input Voltage Noise
VCM = 2.1 V, Over Temperature
(5)
-900
900
1160
VCM = 2.1 V
12
f > 10 kHz
PSRR
CMRR
(1)
(2)
(3)
(4)
(5)
(6)
µA
nV/√Hz
20
50
Gain LMP8640-H LMP8640HV-H
100
V/V
VCM = 2.1 V
-0.25%
0.25%
VCM = 2.1 V, Over Temperature
-0.51%
0.51%
Accuracy over temperature (5)
VCM = 2.1V, Over Temperature
Power Supply Rejection Ratio
VCM = 2.1 V, 2.7 V < V+ < 12 V,
85
LMP8640HV 2.1 V < VCM < 42 V
LMP8640 2.1 V < VCM< 42 V
103
LMP8640HV 2.1 V < VCM < 76 V
95
-2 V TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the
device may be permanently degraded, either mechanically or electrically.
Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlations using
statistical quality control (SQC) method.
Typical values represent the most likely parametric norm at the time of characterization. Actual typical values may vary over time and
will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped production
material.
Offset voltage temperature drift is determined by dividing the change in VOS at the temperature extremes by the total temperature
change.
This parameter is ensured by design and/or characterization and is not tested in production.
Positive Bias Current corresponds to current flowing into the device. Spec does not include input signal dependent currents on the
positive input of approximately Vsense / 5KΩ due to topology feedback action.
Copyright © 2010–2014, Texas Instruments Incorporated
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5
LMP8640, LMP8640-Q1, LMP8640HV
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
Electrical Characteristics 2.7 V
(1)
www.ti.com
(continued)
Unless otherwise specified, all limits ensured for at TA = 25°C, VS= V+ – V-, VSENSE= +IN-(-IN), V+ = 2.7 V, V− = 0 V, −2 V <
VCM < 76 V, RL = 10 MΩ. LMP8640 limits also apply to the LMP8640-Q1.
PARAMETER
BW
TYP (3)
DC VSENSE = 67.5 mV,
CL = 30 pF,RL= 1MΩ
950
Fixed Gain LMP8640-F
LMP8640HV-F (5)
DC VSENSE =27 mV,
CL = 30 pF, RL= 1MΩ
450
Fixed Gain LMP8640-H
LMP8640HV-H (5)
DC VSENSE = 13.5 mV,
CL = 30 pF ,RL= 1 MΩ
230
VCM =5 V, CL = 30 pF, RL = 1 MΩ,
LMP8640-T LMP8640HV-T VSENSE =100 mVpp,
LMP8640-F LMP8640HV-F VSENSE =40 mVpp,
LMP8640-H LMP8640HV-H VSENSE =20 mVpp,
1.4
VCM = 2.1 V
420
600
2000
2500
(7) (5)
Slew Rate
RIN
Differential Mode Input Impedance (5)
VCM = −2 V, Over Temperature
Maximum Output Voltage
CLOAD
(7)
kΩ
µA
2750
VCM = 2.1 V
Minimum Output Voltage
V/µs
800
VCM = −2 V
UNIT
kHz
5
VCM = 2.1 V, Over Temperature
Supply Current
VOUT
MAX (2)
Fixed Gain LMP8640-T
LMP8640HV-T (5)
SR
IS
MIN (2)
TEST CONDITIONS
2.65
V
LMP8640-T LMP8640HV-T
VCM = 2.1 V
18.2
LMP8640-F LMP8640HV-F
VCM = 2.1 V
40
LMP8640-H LMP8640HV-H
VCM = 2.1 V
80
Max Output Capacitance Load (5)
30
mV
pF
The number specified is the average of rising and falling slew rates and measured at 90% to 10%.
7.7 Electrical Characteristics 5 V
(1)
Unless otherwise specified, all limits ensured for at TA = 25°C, VS= V+ – V-, VSENSE= +IN-(-IN), V+ = 5 V, V− = 0 V, −2 V < VCM
< 76 V, RL = 10 MΩ. LMP8640 electrical limits also apply to the LMP8640-Q1 unless noted.
PARAMETER
VCM = 2.1 V
VOS
Input Offset Voltage
TCVOS
Input Offset Voltage Drift (4)
Input Bias Current
eni
Input Voltage Noise
(1)
(2)
(3)
(4)
(5)
(6)
6
VCM = 2.1 V, Over Temperature
(5)
TYP (3)
900
-1160
1160
2.6
13
VCM = 2.1 V, Over Temperature,VSENSE = 0 V
(5)
MAX (2)
-900
VCM = 2.1 V
VCM = 2.1 V, VSENSE = 0 V
(6)
IB
MIN (2)
TEST CONDITIONS
f > 10 kHz
21
28
117
UNIT
µV
µV/°C
µA
nV/√Hz
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No specification of parametric performance is indicated in the electrical tables under
conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the
device may be permanently degraded, either mechanically or electrically.
Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlations using
statistical quality control (SQC) method.
Typical values represent the most likely parametric norm at the time of characterization. Actual typical values may vary over time and
will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped production
material.
Offset voltage temperature drift is determined by dividing the change in VOS at the temperature extremes by the total temperature
change.
This parameter is ensured by design and/or characterization and is not tested in production.
Positive Bias Current corresponds to current flowing into the device. Spec does not include input signal dependent currents on the
positive input of approximately Vsense / 5KΩ due to topology feedback action.
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www.ti.com
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
Electrical Characteristics 5 V
(1)
(continued)
Unless otherwise specified, all limits ensured for at TA = 25°C, VS= V+ – V-, VSENSE= +IN-(-IN), V+ = 5 V, V− = 0 V, −2 V < VCM
< 76 V, RL = 10 MΩ. LMP8640 electrical limits also apply to the LMP8640-Q1 unless noted.
PARAMETER
MIN (2)
TEST CONDITIONS
Gain LMP8640-T LMP8640HV-T
Gain AV
CMRR
50
Gain LMP8640-H LMP8640HV-H
100
BW
-0.25%
0.25%
VCM = 2.1 V, Over Temperature
-0.51%
0.51%
−40°C to 125°C, VCM=2.1 V
Power Supply Rejection Ratio
VCM = 2.1 V, 2.7V < V+ < 12 V,
26.2 ppm/°C
85
LMP8640HV 2.1 V < VCM < 42 V
LMP8640 2.1 V < VCM< 42 V
103
LMP8640HV 2.1 V < VCM < 76 V
95
-2 V 10 kHz
SR
(1)
1160
20
Accuracy over temperature
CMRR
-1160
Gain LMP8640-T LMP8640HV-T
(5)
MAX (2)
900
VCM = 2.1 V, Over Temperature, VSENSE = 0 V
Gain error
PSRR
TYP (3)
-900
VCM = 2.1 V, VSENSE = 0 V
(6)
IB
MIN (2)
TEST CONDITIONS
5
kHz
V/µs
kΩ
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No specification of parametric performance is indicated in the electrical tables under
conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond which the
device may be permanently degraded, either mechanically or electrically.
Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlations using
statistical quality control (SQC) method.
Typical values represent the most likely parametric norm at the time of characterization. Actual typical values may vary over time and
will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped production
material.
Offset voltage temperature drift is determined by dividing the change in VOS at the temperature extremes by the total temperature
change.
This parameter is ensured by design and/or characterization and is not tested in production.
Positive Bias Current corresponds to current flowing into the device. Spec does not include input signal dependent currents on the
positive input of approximately Vsense / 5KΩ due to topology feedback action.
The number specified is the average of rising and falling slew rates and measured at 90% to 10%.
Submit Documentation Feedback
Copyright © 2010–2014, Texas Instruments Incorporated
Product Folder Links: LMP8640 LMP8640-Q1 LMP8640HV
LMP8640, LMP8640-Q1, LMP8640HV
www.ti.com
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
Electrical Characteristics 12 V
(1)
(continued)
Unless otherwise specified, all limits ensured for at TA = 25°C, VS= V+ – V-, VSENSE= +IN-(-IN), V+ = 12 V, V− = 0V, −2 V < VCM
< 76 V, RL = 10 MΩ. LMP8640 electrical limits also apply to the LMP8640-Q1 unless noted.
PARAMETER
MIN (2)
TEST CONDITIONS
VCM = 2.1 V
IS
TYP (3)
MAX (2)
720
1050
VCM = 2.1 V, Over Temperature
Supply Current
1250
VCM = −2 V
2300
VCM = −2 V, Over Temperature
Maximum Output Voltage
VOUT
CLOAD
11.85
V
LMP8640-T LMP8640HV-T
VCM = 2.1 V
18.2
LMP8640-F LMP8640HV-F
VCM = 2.1 V
40
LMP8640-H LMP8640HV-H
VCM = 2.1 V
80
Max Output Capacitance Load (5)
Copyright © 2010–2014, Texas Instruments Incorporated
µA
3000
VCM = 2.1 V
Minimum Output Voltage
2800
UNIT
30
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mV
pF
9
LMP8640, LMP8640-Q1, LMP8640HV
SNOSB28G – AUGUST 2010 – REVISED NOVEMBER 2014
www.ti.com
7.9 Typical Characteristics
Unless otherwise specified: TA = 25°C, VS=V+-V-, VSENSE= +IN - (-IN), RL = 10 MΩ.
2300
2400
2100
VCM=-2V
2500
2200
2100
IS (PA)
125°C
700
600
500
5.3
8.0
10.6
125°C
1300
1100
25°C
-40°C
900
700
500
400
300
2.7
1500
300
-2 -1 0
13.2
1
2
3
Figure 1. Supply Curent vs. Supply Voltage
Figure 2. Supply Current vs. VCM
2300
2500
VS = 5V
1900
2100
1700
1900
1500
125°C
1300
1100
1700
-40°C
900
1100
900
500
700
|
700
1
2
3
125 °C
1500
1300
25°C
300
-2 -1 0
VS = 12V
2300
IS (PA)
IS (PA)
2100
25°C
-40°C
500
-2 -1 0
4 16 28 40 52 64 76
1
2
VCM (V)
140
130
130
120
CMRR (dB)
25°C
125 °C
110
4 16 28 40 52 64 76
Figure 4. Supply Current vs. VCM
140
120
3
VCM (V)
Figure 3. Supply Current vs. VCM
CMRR (dB)
4 16 28 40 52 64 76
VCM (V)
VS (V)
|
|
800
25°C
-40°C
1700
VCM = 2.1V
1900
|
IS (PA)
2000
1900
|
2300
VS = 2.7V
-40°C
100
-40°C
25°C
110
100
90
90
VS = 5V
80
-2
11
24
37
50
63
VS = 5V
76
80
-2
11
Figure 5. CMRR vs. VCM (Gain 20 V/V)
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24
37
50
63
76
V CM (V)
VCM (V)
10
125°C
Figure 6. CMRR vs. VCM (Gain 50 V/V)
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Typical Characteristics (continued)
Unless otherwise specified: TA = 25°C, VS=V+-V-, VSENSE= +IN - (-IN), RL = 10 MΩ.
200
140
VS = 5V
-40°C
150
130
CMRR (dB)
25°C
VOS (PV)
100
120
125°C
110
125 °C
50
0
25°C
-50
100
-100
90
-40°C
-150
V S = 5V
80
-2
11
24
37
50
63
-200
-2
76
11
24
37
Figure 7. CMRR vs. VCM (Gain 100 V/V)
76
100
0
0
-100
-100
-200 -40°C
-400
-40°C
-200
125°C
-300
(µA)
IB (PV)
(µA)
IB (PV)
63
Figure 8. Input Voltage Offset vs. VCM
100
25°C
125 °C
-300
-400
-500
-500
-600
-600
25°C
-700
-700
-800
-800
VS = 2.7V
-900
-2 -1 0
1
2
3
VS = 5V
-900
-2 -1 0
4 16 28 40 52 64 76
1
2
3
4 16 28 40 52 64 76
VCM (V)
VCM (V)
Figure 9. Ibias vs. VCM
Figure 10. Ibias vs. VCM
50
100
0
-100
50
V CM (V)
V CM (V)
VS =5V, VCM=5V
GAIN 100V/V
-40°C
40
125°C
-300
-400
GAIN (dB)
IB (PV)
(µA)
-200
25°C
-500
30
GAIN 50V/V
-600
20
GAIN 20V/V
-700
-800
VS = 12V
-900
-2 -1 0
1
2
3
4 16 28 40 52 64 76
10
100
1k
10k
100k
1M
10M
VCM (V)
FREQUENCY (Hz)
Figure 11. Ibias vs. VCM
Figure 12. Gain vs. Frequency
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Typical Characteristics (continued)
13.0
12.0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
300
VS =12V, VCM =12V
V S=12V, VCM=12V
250
GAIN 100V/V
200
VOUT (mV)
VOUT (V)
Unless otherwise specified: TA = 25°C, VS=V+-V-, VSENSE= +IN - (-IN), RL = 10 MΩ.
GAIN 100V/V
GAIN 50V/V
150
100
GAIN 20V/V
GAIN 50V/V
50
GAIN 20V/V
100
200
300
400
500
0
-3
600
-2
-1
0
1
2
3
VSENSE (mV)
VSENSE (mV)
Figure 13. Output voltage vs. VSENSE
Figure 14. Output Voltage vs. VSENSE (ZOOM Close to 0 V)
VSENSE
GAIN 50V/V
GAIN 20V/V
VSENS E (10 mV/DIV)
GAIN 100
VOUT (100 mV/DIV)
VS ENS E (20 mV/DIV)
VOUT (500 mV/DIV)
V SENSE
GAIN 100V/V
GAIN 50V/V
GAIN 20V/V
V S = 5V, VCM = 12V
VS =12V, VCM =12V
TIME (2 Ps/DIV)
TIME (2 Ps/DIV)
Figure 16. Small Step Response
Figure 15. Large Step Response
VS = 5V, VCM = 12V
GAIN 100V/V
GAIN 100 V/V
V SENSE
GAIN 20V/V
GAIN 50V/V
GAIN 20V/V
VSE NSE (10 mV/DIV)
GAIN 50V/V
VOUT (100 mV/DIV)
V SE NS E (10 mV/DIV)
V OUT (100 mV/DIV)
V SENSE
VS = 5V, V CM = 12V
TIME (400 ns /DIV)
Figure 17. Settling Time (Fall)
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TIME (400 ns/DIV)
Figure 18. Settling Time (Rise)
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Typical Characteristics (continued)
V OUT
VCM
VCM (5V/DIV)
VCM (5V/DIV)
V CM
VOUT (50 mV/DIV)
V OUT (20 mV/DIV)
Unless otherwise specified: TA = 25°C, VS=V+-V-, VSENSE= +IN - (-IN), RL = 10 MΩ.
VOUT
VS = 5V, GAIN 20 V/V
VS = 5V, GAIN 20 V/V
TIME (4 és/DIV)
TIME (4 és/DIV)
Figure 19. Common Mode Step Response (Rise)
Figure 20. Common Mode Step Response (Fall)
2.505
2.6
VS =5V, VCM=12V
2.504
2.5
GAIN 100 V/V
2.4
2.502
V OUT (V)
V OUT (V)
2.503
GAIN 50
2.501
GAIN 20V/V
2.500
GAIN 100V/V
2.3
2.2
GAIN 50
2.1
2.499
2.0
GAIN 20V/V
VS =5V, VCM=12V
2.498
0
1
2
3
4
5
6
7
8
9
1.9
0
10
1
2
3
4
I OUT (mA)
5
Figure 21. Load Regulation (Sinking)
7
8
9
10
Figure 22. Load Regulation (Sourcing)
110
100
V S = 5V, V CM = 12V
VS = 5V, VCM = 12V
80
90
CMRR (dB)
PSRR (dB)
6
I OUT (mA)
60
GAIN 20V/V
40
70
GAIN 100V/V
50
GAIN 50V/V
GAIN 100 V/V
20
30
GAIN 20V/V
GAIN 50V/V
0
10
100
1k
10k
100k
1M
10
1
10
FREQUENCY (Hz)
Figure 23. AC PSRR vs. Frequency
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100
1k
10k
100k
Frequency (Hz)
Figure 24. AC CMRR vs. Frequency
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8 Detailed Description
8.1 Overview
The LMP8640 and LMP8640HV are single supply high side current sense amplifiers with a fixed gain of 20 V/V,
50 V/V, 100 V/V and a common mode voltage range of -2 V to 42 V (LMP8640-x) or -2 V to 76 V (LMP8640HVx) with a buffered voltage output.
8.2 Functional Block Diagram
+IN
-IN
RIN LMP8640
RIN
LMP8640HV
+
+
V
G
VOUT
RG = 2*RIN
V
-
8.3 Feature Description
As seen in Figure 25, the current flowing through sense resistor RS develops a voltage drop equal to VSENSE
across RS. The voltage at the -IN pin will now be less than +IN by an amount proportional to the VSENSE voltage.
VSENSE
Is
+
Rs
+IN
-IN
RIN
+
LMP8640
RIN
L
o
a
d
+
V
IG
G
VOUT
RG = 2*RIN
V
-
Figure 25. Simple Current Monitor
The low bias currents of the error amplifier cause little voltage drop through RIN-, so the negative input of the
internal error amplifier is at essentially the same potential as the -IN input. The RIN resistors are 5 KΩ each.
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Feature Description (continued)
The error amplifier will detect this voltage error between it's inputs and drive the MOSFET gate to conduct more
current, increasing the voltage drop across RIN+, until the servo amplifiers positive input matches the negative
input. At this point, the voltage drop across RIN+ now matches VSENSE.
IG, a current proportional to IS, will flow according to the following relation:
IG = VSENSE/RIN = RS* IS/RIN
(1)
IG also flows through the internal gain resistor RG developing a voltage drop equal to:
VRG = IG * RG = (VSENSE/RIN) * RG = ((RS* IS)/ RIN )* RG
VOUT = 2*(RS*IS)*G,
(2)
(3)
where G=RG/RIN = 10 V/V, 25 V/V or 50 V/V, according to the gain option selected.
The voltage on RG is then amplified by a gain of 2 by the output gain stage to create the final overall gain of x20,
x50 and x100. The output stage has a low impedance drive allowing the LMP8640 to easily interface with other
IC's (ADC, Mux, µC…). No external buffering is required.
8.3.1 Selection of Sense Resistor
The value chosen for the shunt resistor, RS, depends on the application. It plays a big role in a current sensing
system and must be chosen with care. The selection of the shunt resistor needs to take in account the tradeoffs
in small-signal accuracy, the power dissipated and the voltage loss across the shunt itself.
In applications where a small current is sensed, a bigger value of RS is selected to minimize the error in the
proportional output voltage. Higher resistor value improves the signal-to-noise ratio (SNR) at the input of the
current sense amplifier and hence gives a more accurate output.
Similarly when high current is sensed, the power losses in RS can be significant so a smaller value of RS is
desired. In this condition it is also required to take in account also the power rating of RS resistor. The low input
offset of the LMP8640 allows the use of small sense resistors to reduce power dissipation still providing a good
input dynamic range. The input dynamic range is the ratio between the maximum signal that can be measured
and the minimum signal that can be detected, where usually the input offset is the principal limiting factor.
Figure 26. Example of a Kelvin (4-Wire) Connection to a Two-Terminal Resistor
The amplifier inputs should be directly connected to the sense resistor pads using “Kelvin” or “4-wire” connection
techniques. The paths of the input traces should be identical, including connectors and vias, so that these errors
will be equal and cancel.
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Feature Description (continued)
8.3.1.1 Resistor Power Rating and Thermal Issues
The power dissipated by the sense resistor can be calculated from:
PD = IMAX2 * RS
where
•
•
•
PD is the power dissipated by the resistor in Watts
IMAX is the maximum load current in Amps
RS is the sense resistor value in ohms.
(4)
The resistor must be rated for more than the expected maximum power (PD), with margin for temperature
derating. Be sure to observe any power derating curves provided by the resistor manufacturer.
Running the resistor at higher temperatures will also affect the accuracy. As the resistor heats up, the resistance
generally goes up, which will cause a change in the measurement. The sense resistor should have as much
heat-sinking as possible to remove this heat through the use of heatsinks or large copper areas coupled to the
resistor pads. A reading drifting slightly after turn-on can usually be traced back to sense resistor heating.
8.3.1.2 Using PCB Trace as a Sense Resistor
While it may be tempting to use the resistance of a known area of PCB trace or copper area as a sense resistor,
it is not recommended for precision measurements.
The tempco of copper is typically 3300-4000ppm/°K (0.33% to 0.4% per °C), which can vary with PCB
processes.
A typical surface mount sense resistor temperature coefficient (tempco) is in the 50ppm to 500ppm per °C range
offering more measurement consistency and accuracy over the copper trace. Special low tempco resistors are
available in the 0.1 to 50ppm range, but at a much higher cost.
8.3.2 Sense Line Inputs
The sense lines should be connected to a point on the resistor that is not shared with the main current path, as
shown in Figure 26 above. For lowest drift, the amplifier should be mounted away from any heat generating
devices, which may include the sense resistor. The traces should be one continuous trace of copper from the
sense resistor pad to the amplifier input pin pad, and ideally on the same copper layer with minimal vias or
connectors. This can be important around the sense resistor if it is generating any significant heat gradients. Vias
in the sense lines should be formed from continuous plated copper and routing through connectors should be
avoided. It is better to extend the sense lines than to place the amplifier in a hostile environment.
To minimize noise pickup and thermal errors, the input traces should be treated like a high-speed differential
signal pair and routed tightly together with a direct path to the input pins on the same copper layer. They do not
need to be "impedance matched", but should follow the same matching rules about vias, spacing and equal
lengths. The input traces should be run away from noise sources, such as digital lines, switching supplies or
motor drive lines. Remember that these input traces can contain high voltage, and should have the appropriate
trace routing clearances to other traces and layers. Since the sense traces only carry the amplifier bias current
(typically about 12µA per input at room temp), the connecting input traces can be thin traces running close
together. This can help with routing or creating the required spacings.
It should also be noted that, due to the nature of the device topology, the positive input bias current will vary with
VSENSE with an extra current approximately equivalent to VSENSE / 5 kΩ on top of the typical 12 uA bias current.
The negative input bias current is not in the feedback path and will not change over VSENSE. High or missmatched source impedances should be avoided as this imbalance will create an additional error over input
voltage.
8.3.3 Effects of Series Resistance on Sense Lines
Because the input stage uses precision 5 KΩ resistors internally to convert the voltage on the input pin to a
current, any resistance added in series with the input pins will change this resistance, and thus alter the gain.
If a resistance is added in series with an input, the gain of that input will not track that of the other input, causing
a constant gain error.
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Feature Description (continued)
It is not recommended to use external resistance to alter the gain, as external resistors will not have the same
thermal matching as the internal thin film resistors. Any added resistance will severely degrade the offset and
CMRR specifications. It is recommended that the total trace resistance be less than 10 ohms.
If resistors are purposely added for filtering, resistance should be added equally to both inputs and the user
should be aware that the gain will change slightly.
8.4 Device Functional Modes
8.4.1 Bias Current at Low Common Mode Voltage
At common mode voltages below +2 V, the input bias current starts to reverse and crosses through zero at about
+1.8 V. This can be seen in the Input Bias Current graphs in Figure 9 through Figure 11. Negative currents on
the graph show curent flow out of the input and into the load. The graphs show the current for each input, so the
actual "bias" current will be twice graph value. This total current could be as high as 1mA, depending on the point
of equilibrium.
While this will not affect the vast majority of applications, it may cause MOSFET switched designs with non-linear
loads (like LED's or diode-isolated loads) to "float" above ground where the load leakage and bias currents attain
equilibrium. A small resistor to ground (on the load supply side) can bleed-off this current.
8.4.2 Applying Input Voltage with No Supply Voltage
The full specified input common mode voltage range may be applied to the inputs while the LMP8640 power is
off (V+ = 0 V). When the LMP8640 is powered off, the RIN resistors are disconnected internally by MOSFETS
and the leakage currents are very low (sub uA).
The 6 V input differential limit still applies, so at no time should the two inputs be more than 6 V apart. There are
also Zener clamps on the inputs to ground, so do not exceed the input limits specified in the Absolute Maximum
Ratings.
8.4.3 Driving an ADC
The input stage of an Analog to Digital converter can be modeled with a resistor and a capacitance to ground. So
if the voltage source doesn't have a low impedance, an error in amplitude measurement will occur. In this case, a
buffer is needed to drive the ADC. The LMP8640 has an internal output buffer able to directly drive a capacitive
load up to 30 pF, or, the input stage of an ADC. It is recommended that an external low pass RC filter be added
to the output of the LMP8640 to reduce the noise and limit the bandwidth of the current sense measurement.
If the supply voltage of the LMP8640 is higher than the ADC supply voltage, care should be taken to prevent the
LMP8640 output from over-driving the ADC input.
This can be accomplished with a series resistance (which should be present when driving a ADC) and a
clamping diode to the ADC's power supply. The diode will clamp the ADC input to a safe level. Do not completely
rely on a calculated maximum output voltage. Transients or fault conditions outside the normal conditions area
can cause the output to swing to a higher than expected voltage.
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The LMP8640x amplifies the voltage developed across a current-sensing resistor.
9.2 Typical Application
IS
RS
+
+IN
-IN
RIN
+
L
o
a
d
LMP8640
RIN
+
V
+
VA
RF
G
ADC
VOUT
CF
RG = 2*RIN
-
V
Figure 27. Typical Application Example
9.2.1 Design Requirements
In this example, a current monitor application is required to measure the current into a load (peak current 10 A)
with a resolution of 10 mA and 0.5% of accuracy.
The 10bit analog to digital converter accepts a max input voltage of 4.1 V. In order to not burn too much power
on the shunt resistor, it needs to be less than 10 mΩ. Table 1 below summarizes the other design conditions.
Table 1. Example Design Requirements
WORKING CONDITION
VALUE
MIN
MAX
Supply Voltage
5V
5.5 V
Common mode Voltage
48 V
70 V
Temperature
0°C
70°C
Signal BW
50 kHz
9.2.2 Design Procedure
9.2.2.1 First Step – LMP8640 or LMP8640HV Selection
The required common mode voltage of the application implies that the right choice is the LMP8640HV (High
common mode voltage up tp 76 V).
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9.2.2.2 Second Step – Gain Option Selection
We can choose between three gain option (20 V/V, 50 V/V, 100 V/V). Considering the max input voltage of the
ADC (4.1 V) , the max Sense voltage across the shunt resistor is evaluated according the following formula:
VSENSE= (MAX Vin ADC) / Gain;
(5)
hence the max VSENSE will be 205 mV, 82 mV, 41 mV respectively. The shunt resistor are then evaluated
considering the maximum monitored current :
RS = (max VSENSE) / I_MAX
(6)
For each gain option the max shunt resistors are the following : 20.5 mΩ, 8.2 mΩ, 4.1 mΩ respectively.
One of the project constraints requires RS
