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INA281
SBOSA29 – JUNE 2020
INA281, –4-V to 110-V, 1.3-MHz Current-Sense Amplifier
1 Features
3 Description
•
The INA281 is a high-precision current sense
amplifier that can measure voltage drops across
shunt resistors over a wide common-mode range
from –4 V to 110 V. The negative common-mode
voltage allows the device to operate below ground,
thus accommodating precise measurement of
recirculating currents in half-bridge applications. The
combination of a low offset voltage, small gain error
and high DC CMRR enables highly accurate current
measurement. The INA281 is not only designed for
DC current measurement, but also for high-speed
applications (like fast overcurrent protection, for
example) with a high bandwidth of 1.3 MHz and an
65-dB AC CMRR (at 50 kHz).
1
•
•
•
•
•
•
Wide common-mode voltage:
– Operational voltage: −4 V to +110 V
– Survival voltage: −20 V to +120 V
Excellent CMRR:
– 120-dB DC CMRR
– 65-dB AC CMRR at 50 kHz
Accuracy:
– Gain:
– Gain error: ±0.5% (maximum)
– Gain drift: ±20 ppm/°C (maximum)
– Offset:
– Offset voltage: ±55 µV (typical)
– Offset drift: ±0.1 µV/°C (typical)
Available gains:
– INA281A1, INA281B1 : 20 V/V
– INA281A2, INA281B2 : 50 V/V
– INA281A3, INA281B3 : 100 V/V
– INA281A4, INA281B4 : 200 V/V
– INA281A5, INA281B5 : 500 V/V
High bandwidth: 1.3 MHz
Slew rate: 2.5V/µs
Quiescent current: 1.5 mA
The INA281 operates from a single 2.7-V to 20-V
supply, drawing 1.5 mA of supply current. The
INA281 is available with five gain options: 20 V/V, 50
V/V, 100 V/V, 200 V/V, and 500 V/V. These gain
options address wide dynamic range for currentsensing applications.
The INA281 is specified over an operating
temperature range of −40 °C to +125 °C and is
offered in a space-saving SOT-23 package with two
pin-out variants.
Device Information(1)
PART NUMBER
INA281
2 Applications
•
•
•
•
•
•
•
•
Active antenna system mMIMO (AAS)
Macro remote radio unit (RRU)
48-V rack server
48-V merchant network & server power supply
(PSU)
Solenoid control
Valve control
Telecom equipment
Power supplies
PACKAGE
SOT-23 (5)
BODY SIZE (NOM)
2.90 mm × 1.60 mm
(1) For all available packages, see the package option addendum
at the end of the data sheet.
Functional Block Diagram
VS
VCM
ISENSE
R1
IN+
RSENSE
+
Bias
R1
IN±
Load
Current
Feedback
OUT
-
Buffer
RL
GND
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.
INA281
SBOSA29 – JUNE 2020
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
6.1
6.2
6.3
6.4
6.5
6.6
3
3
4
4
4
6
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
7.4 Device Functional Modes........................................ 13
8
Application and Implementation ........................ 14
8.1 Application Information............................................ 14
8.2 Typical Application .................................................. 16
9 Power Supply Recommendations...................... 17
10 Layout................................................................... 18
10.1 Layout Guidelines ................................................. 18
10.2 Layout Example .................................................... 18
11 Device and Documentation Support ................. 19
11.1
11.2
11.3
11.4
11.5
11.6
Detailed Description ............................................ 11
7.1 Overview ................................................................. 11
7.2 Functional Block Diagram ....................................... 11
7.3 Feature Description................................................. 11
Documentation Support ........................................
Receiving Notification of Documentation Updates
Support Resources ...............................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
19
19
19
19
19
19
12 Mechanical, Packaging, and Orderable
Information ........................................................... 19
4 Revision History
2
DATE
REVISION
NOTES
June 2020
*
Initial release
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5 Pin Configuration and Functions
INA281A: DBV Package
5-Pin SOT-23
Top View
OUT
1
GND
2
IN+
3
5
4
INA281B: DBV Package
5-Pin SOT-23
Top View
Vs
IN±
OUT
1
GND
2
Vs
3
Not to scale
5
IN±
4
IN+
Not to scale
Pin Functions
PIN
NAME
TYPE
DESCRIPTION
INA281A
INA281B
GND
2
2
Ground
IN–
4
5
Input
Shunt resistor negative sense input
IN+
3
4
Input
Shunt resistor positive sense input
OUT
1
1
Output
Output voltage
Vs
5
3
Power
Power supply
Ground
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
Supply Voltage
(VS)
Differential (VIN+) – (VIN–), INA281A5, INA281B5
Analog Inputs,
VIN+, VIN– (2)
–0.3
22
UNIT
V
–6
6
–12
12
Common-mode
–20
120
GND – 0.3
VS + 0.3
V
–55
150
°C
150
°C
150
°C
TA
Operating temperature
TJ
Junction temperature
Tstg
Storage temperature
(2)
MAX
Differential (VIN+) – (VIN–), All others
Output
(1)
MIN
–65
V
Stresses beyond those listed under Absolute Maximum Rating may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Condition. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
VIN+ and VIN– are the voltages at the IN+ and IN– pins, respectively.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human body model (HBM), per
ANSI/ESDA/JEDEC JS-001, all pins (1)
±2000
Charged device model (CDM), per JEDEC
specification JESD22-C101, all pins (2)
±1000
UNIT
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.
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6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
UNIT
VCM
Common-mode input range
–4
48
110
V
VS
Operating supply range
2.7
5
20
V
VSENSE
Differential sense input range
TA
Ambient temperature
0
VS / G
V
–40
125
°C
6.4 Thermal Information
INA281
THERMAL METRIC
(1)
DBV (SOT-23)
UNIT
5 PINS
RθJA
Junction-to-ambient thermal resistance
184.7
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
105.6
°C/W
RθJB
Junction-to-board thermal resistance
47.2
°C/W
ΨJT
Junction-to-top characterization parameter
21.5
°C/W
ΨJB
Junction-to-board characterization parameter
46.9
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
N/A
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
6.5 Electrical Characteristics
at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
110
V
INPUT
VCM
Common-mode input range (1)
CMRR
Common-mode rejection ratio, input
referred
Vos
Offset voltage, input referred
TA = –40 °C to +125 °C
–4 V ≤ VCM ≤ 110 V, TA = –40 °C to
+125 °C
–4
120
140
dB
f = 50 kHz
65
dB
INA281x1
±100
±500
INA281x2
±55
±300
INA281x3
±30
±250
INA281x4
±30
±200
µV
INA281x5
±15
±150
dVos/dT
Offset voltage drift
TA = –40 ℃ to +125 ℃
±0.1
±1
µV/℃
PSRR
Power supply rejection ratio, input
referred
2.7 V ≤ VS ≤ 20 V,
TA = –40 °C to +125 °C
±1.5
±10
µV/V
IB
Input bias current
(1)
4
IB+, VSENSE = 0 V
10
20
30
uA
IB–, VSENSE = 0 V
10
20
30
uA
Common-mode voltage at both VIN+ and VIN- must not exceed the specified common-mode input range.
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Electrical Characteristics (continued)
at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
OUTPUT
G
Gain
GERR
Gain error
NLERR
Nonlinearity error
Maximum capacitive load
INA281x1
20
V/V
INA281x2
50
V/V
INA281x3
100
V/V
INA281x4
200
V/V
INA281x5
500
GND + 50 mV ≤ VOUT ≤ VS – 200 mV
TA = –40 °C to +125 °C
No sustained oscillations, no isolation
resistor
V/V
±0.07
±0.5
%
±2
±20
ppm/°C
0.01
%
500
pF
VOLTAGE OUTPUT
VS –
0.07
VS –
0.15
V
RLOAD = 10 kΩ, VSENSE = 0 V,
TA = –40 °C to +125 °C
0.005
0.02
V
INA281x1, CLOAD = 5 pF,
VSENSE = 200 mV
1300
INA281x2, CLOAD = 5 pF,
VSENSE = 80 mV
1300
INA281x3, CLOAD = 5 pF,
VSENSE = 40 mV
1000
INA281x4, CLOAD = 5 pF,
VSENSE = 20 mV
900
INA281x5, CLOAD = 5 pF,
VSENSE = 8 mV
900
Rising edge
2.5
VOUT = 4 V ± 0.1 V step, Output settles
to 0.5%
10
VOUT = 4 V ± 0.1 V step, Output settles
to 1%
5
VOUT = 4 V ± 0.1 V step, Output settles
to 5%
1
Swing to Vs (Power supply rail)
RLOAD = 10 kΩ, TA = –40 °C to +125 °C
Swing to ground
FREQUENCY RESPONSE
BW
SR
Bandwidth
Slew rate
Settling time
kHz
V/µs
µs
NOISE
Ven
Voltage noise density
50
nV/√Hz
POWER SUPPLY
Vs
IQ
Supply voltage
Quiescent current
TA = –40 °C to +125 °C
2.7
1.5
TA = –40 °C to +125 °C
20
V
2
mA
2.25
mA
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6.6 Typical Characteristics
All specifications at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V, unless otherwise noted.
160
100
0
G
G
G
G
G
-100
-200
-75
-50
-25
0
25
50
75 100
Temperature (qC)
125
=
=
=
=
=
20
50
100
200
500
150
Common-Mode Rejection Ratio (dB)
Common-Mode Rejection Ratio (nV/V)
200
140
120
100
80
60
40
20
0
10
175
100
1k
10k
Frequency (Hz)
100k
Figure 2. Common-Mode Rejection Ratio vs Frequency
Figure 1. Common-Mode Rejection Ratio vs Temperature
0.250
60
G
G
G
G
G
50
0.125
Gain Error (%)
Gain (dB)
40
30
20
10
0
-10
10
G
G
G
G
G
=
=
=
=
=
20
50
100
200
500
100
1k
10k
100k
Frequency (Hz)
1M
-0.250
-75
10M
-50
20
20
15
VS
VS
VS
VS
10
5
=
=
=
=
5V
20V
2.7V
0V
0
0
25
50
75 100
Temperature (qC)
VS
VS
VS
VS
VS
15
10
5
125
150
175
100
120
=
=
=
=
=
2.7 to 20V, VCM = 48V
2.7 to 20V, VCM = 120V
2.7 to 20V, VCM = -4V
0V, VCM = 120V
0V, VCM = -4V
0
VS = 0V and 20V, VCM = -20V
-5
-5
20
40
60
80
Common-Mode Voltage (V)
-25
Figure 4. Gain Error vs Temperature
25
Input Bias Current (PA)
Input Bias Current (PA)
20
50
100
200
500
-0.125
Figure 3. Gain vs Frequency
0
=
=
=
=
=
0.000
25
-10
-20
1M
-10
-75
-50
-25
0
25
50
75 100
Temperature (qC)
125
150
175
VSENSE = 0 V
Figure 5. Input Bias Current vs Common-Mode Voltage
6
Figure 6. Input Bias Current vs Temperature
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Typical Characteristics (continued)
All specifications at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V, unless otherwise noted.
240
140
IB+
IBIB+, VS = 0V
IB-, VS = 0V
Input Bias Current (PA)
160
100
120
80
40
0
-40
80
60
40
20
0
-20
-80
-40
-120
-60
-160
-80
0
200
400
600
VSENSE (mV)
800
1000
0
Figure 7. INA281x1 Input Bias Current vs VSENSE
100
200
VSENSE (mV)
300
400
Figure 8. INA281x2, INA281x3 Input Bias Current vs VSENSE
100
VS
IB+, G=200
IB+, G=500
IBIB+, VS = 0V
IB-, VS = 0V
60
25qC
125qC
-40qC
VS - 1
Output Voltage (V)
80
Input Bias Current (PA)
IB+
IBIB+, VS = 0V
IB-, VS = 0V
120
Input Bias Current (PA)
200
40
20
0
VS - 2
GND + 2
GND + 1
-20
GND
0
20
40
60
VSENSE (mV)
80
100
0
5
10
15
20
25
Output Current (mA)
30
35
40
VS = 2.7 V
Figure 9. INA281x4, INA281x5 Input Bias Current vs VSENSE
Figure 10. Output Voltage vs Output Current
VS
VS
25qC
125qC
-40qC
VS - 2
VS - 3
GND + 3
VS - 2
VS - 3
GND + 3
GND + 2
GND + 2
GND + 1
GND + 1
GND
25qC
125qC
-40qC
VS - 1
Output Voltage (V)
Output Voltage (V)
VS - 1
GND
0
5
10
15
20
25
Output Current (mA)
30
35
VS = 5 V
40
0
5
10
15
20
25
Output Current (mA)
30
35
40
VS = 20 V
Figure 11. Output Voltage vs Output Current
Figure 12. Output Voltage vs Output Current
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Typical Characteristics (continued)
All specifications at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V, unless otherwise noted.
0.00
200
100
50
-0.10
20
10
5
Swing to VS (V)
Output Impedance (:)
1000
500
2
1
0.5
0.2
0.1
0.05
-0.20
-0.30
-0.40
0.02
0.01
10
100
1k
10k
100k
Frequency (Hz)
1M
VS = 5V
VS = 20V
VS = 2.7V
-0.50
-75
10M
-50
Figure 13. Output Impedance vs Frequency
25
50
75 100
Temperature (qC)
125
150
175
0.015
0.010
0.005
-50
-25
0
25
50
75 100
Temperature (qC)
125
150
Input-Referred Voltage Noise (nV/—Hz)
100
VS = 5V
VS = 20V
VS = 2.7V
Swing to GND (V)
0
Figure 14. Swing to Supply vs Temperature
0.020
0.000
-75
-25
G = 20
G = 500
80
70
60
50
40
30
20
10
10
175
100
1k
10k
Frequency (Hz)
100k
1M
Figure 16. Input Referred Noise vs Frequency
Figure 15. Swing to GND vs Temperature
2
Quiescent Current (mA)
Referred-to-Input
Voltage Noise (200 nV/div)
1.8
1.6
VS = 20V
1.4
VS = 5V
1.2
1
VS = 2.7V
G = 20 to 50
G = 100 to 500
0.8
Time (1 s/div)
Figure 17. Input Referred Noise
8
0
2.5
5
7.5
10
12.5
Output Voltage (V)
15
17.5
20
Figure 18. Quiescent Current vs Output Voltage
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Typical Characteristics (continued)
All specifications at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V, unless otherwise noted.
2
50
Quiescent Current (mA)
1.8
Short Circuit Current (mA)
VS = 5V
VS = 20V
VS = 2.7V
1.6
1.4
1.2
1
0.8
-75
-50
-25
0
25
50
75 100
Temperature (qC)
125
150
40
30
0
-75
175
Quiescent Current (mA)
1.8
1.6
1.4
1.2
18
150
175
VS = 5V
VS = 20V
VS = 2.7V
1.4
1.2
0.8
-20
20
Figure 21. Quiescent Current vs Supply Voltage
0
20
40
60
80
Common-Mode Voltage (V)
100
120
Figure 22. Quiescent Current vs Common-Mode Voltage
VCM
VOUT
Output Voltage (2.5V/div)
Common-Mode Voltage (20V/div)
125
0V
0V
Output Voltage
500 mV/div
16
25
50
75 100
Temperature (qC)
1
0.8
8
10
12
14
Supply Voltage (V)
0
1.6
25qC
125qC
-40qC
6
-25
0V
Input Voltage
5 mV/div
Quiescent Current (mA)
1.8
4
-50
Figure 20. Short-Circuit Current vs Temperature
2
2
5V, Sourcing
5V, Sinking
20V, Sourcing
20V, Sinking
2.7V, Sourcing
2.7V, Sinking
10
Figure 19. Quiescent Current vs Temperature
0
=
=
=
=
=
=
20
2
1
VS
VS
VS
VS
VS
VS
0V
Time (10 Ps/div)
Time (12.5Ps/div)
Figure 23. Common-Mode Voltage Fast Transient Pulse
Figure 24. INA281x3 Step Response
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Typical Characteristics (continued)
All specifications at TA = 25 °C, VS = 5 V, VSENSE = VIN+ – VIN– = 0.5 V / Gain, VCM = VIN– = 48 V, unless otherwise noted.
Supply Voltage
Output Voltage
Voltage(1 V/div)
Voltage (1 V/div)
Supply Voltage
Output Voltage
0V
0V
Time (5 Ps/div)
Time (50 Ps/div)
Figure 25. Start-Up Response
10
Figure 26. Supply Transient Response
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7 Detailed Description
7.1 Overview
The INA281 is a high- or low-side current-sense amplifier that offers a wide common-mode range, precision zerodrift topology, excellent common-mode rejection ratio (CMRR), high bandwidth, and fast slew rate. Different gain
versions are available to optimize the output dynamic range based on the application. The INA281 is designed
using a transconductance architecture with a current-feedback amplifier that enables low bias currents of 20 µA
with a common-mode voltage of 110 V.
7.2 Functional Block Diagram
VS
Load
Supply
ISENSE
R1
IN+
RSENSE
+
Bias
R1
IN±
Current
Feedback
OUT
-
Load
Buffer
RL
GND
7.3 Feature Description
7.3.1 Amplifier Input Common-Mode Signal
The INA281 supports large input common-mode voltages from –4 V to +110 V. Because of the internal topology,
the common-mode range is not restricted by the power-supply voltage (VS). This allows for the INA281 to be
used for both low- and high-side current-sensing applications.
7.3.1.1 Input-Signal Bandwidth
The INA281 –3-dB bandwidth is gain-dependent, with several gain options of 20 V/V, 50 V/V, 100 V/V, 200 V/V,
and 500 V/V. The unique multistage design enables the amplifier to achieve high bandwidth at all gains. This
high bandwidth provides the throughput and fast response that is required for the rapid detection and processing
of overcurrent events.
The bandwidth of the device also depends on the applied VSENSE voltage. Figure 27 shows the bandwidth
performance profile of the device over frequency as output voltage increases for each gain variation. As shown in
Figure 27, the device exhibits the highest bandwidth with higher VSENSE voltages, and the bandwidth is higher
with lower device gain options. Individual requirements determine the acceptable limits of error for highfrequency, current-sensing applications. Testing and evaluation in the end application or circuit is required to
determine the acceptance criteria and validate whether or not the performance levels meet the system
specifications.
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Feature Description (continued)
1400
Bandwidth (kHz)
1200
1000
800
600
INA281A1
INA281A2
INA281A3
INA281A4
INA281A5
400
200
0
1
2
3
Output Voltage (V)
Figure 27. Bandwidth vs Output Voltage
7.3.1.2 Low Input Bias Current
The INA281 inputs draw a 20-µA (typical) bias current at a common-mode voltage as high as 110 V, which
enables precision current sensing on applications that require lower current leakage.
7.3.1.3 Low VSENSE Operation
The INA281 operates with high performance across the entire valid VSENSE range. The zero-drift input
architecture of the INA281 provides the low offset voltage and low offset drift needed to measure low VSENSE
levels accurately across the wide operating temperature of –40 °C to +125 °C. Low VSENSE operation is
particularly beneficial when using low ohmic shunts for low current measurements, as power losses across the
shunt are significantly reduced.
7.3.1.4 Wide Fixed Gain Output
The INA281 gain error is < 0.5% at room temperature, with a maximum drift of 20 ppm/°C over the full
temperature range of –40 °C to +125 °C. The INA281 is available in multiple gain options of 20 V/V, 50 V/V, 100
V/V, 200 V/V, and 500 V/V, which the system designer should select based on their desired signal-to-noise ratio
and other system requirements.
The INA281 closed-loop gain is set by a precision, low-drift internal resistor network. The ratio of these resistors
are excellently matched, while the absolute values may vary significantly. TI does not recommend adding
additional resistance around the INA281 to change the effective gain because of this variation, however. The
typical values of the gain resistors are described in Table 1.
Table 1. Fixed Gain Resistor
GAIN
R1
RL
20 (V/V)
25 kΩ
500 kΩ
50 (V/V)
10 kΩ
500 kΩ
100 (V/V)
10 kΩ
1000 kΩ
200 (V/V)
5 kΩ
1000 kΩ
500 (V/V)
2 kΩ
1000 kΩ
7.3.1.5 Wide Supply Range
The INA281 operates with a wide supply range from 2.7 V to 20 V. The output stage supports a wide output
range, while the INA281x1 (gain of 20 V/V) at a supply voltage of 20 V allows a maximum acceptable differential
input of 1 V. When paired with the small input offset voltage of the INA281, systems with very wide dynamic
ranges of current measurement can be supported.
12
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7.4 Device Functional Modes
7.4.1 Unidirectional Operation
The INA281 measures the differential voltage developed by current flowing through a resistor that is commonly
referred to as a current-sensing resistor or a current-shunt resistor. The INA281 operates in unidirectional mode
only, meaning it only senses current sourced from a power supply to a system load as shown in Figure 28.
5V
48-V
Supply
ISENSE
R1
IN+
+
RSENSE
Bias
R1
Current
Feedback
OUT
-
IN±
Buffer
RL
Load
GND
Figure 28. Unidirectional Application
The linear range of the output stage is limited to how close the output voltage can approach ground under zeroinput conditions. The zero current output voltage of the INA281 is very small, with a maximum of GND + 20 mV.
Make sure to apply a differential input voltage of (20 mV / Gain) or greater to keep the INA281 output in the
linear region of operation.
7.4.2 High Signal Throughput
With a bandwidth of 1.3 MHz at a gain of 20 V/V and a slew rate of 2.5 V/µs, the INA281 is specifically designed
for detecting and protecting applications from fast inrush currents. As shown in Table 2, the INA281 responds in
less than 2 µs for a system measuring a 75-A threshold on a 2-mΩ shunt.
Table 2. Response Time
PARAMETER
EQUATION
INA281
AT VS = 5 V
G
Gain
20 V/V
IMAX
Maximum current
100 A
IThreshold
Threshold current
75 A
RSENSE
Current sense resistor value
VOUT_MAX
Output voltage at maximum current
VOUT_MAX = IMAX × RSENSE × G
VOUT_THR
Output voltage at threshold current
VOUT_THR = ITHR × RSENSE × G
SR
Slew rate
Output response time
2 mΩ
4V
3V
2.5 V/µs
Tresponse= VOUT_THR / SR
< 2 µs
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8 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.
8.1 Application Information
The INA281 amplifies the voltage developed across a current-sensing resistor as current flows through the
resistor to the load. The wide input common-mode voltage range and high common-mode rejection of the
INA281 make it usable over a wide range of voltage rails while still maintaining an accurate current
measurement.
8.1.1 RSENSE and Device Gain Selection
The accuracy of any current-sense amplifier is maximized by choosing the current-sense resistor to be as large
as possible. A large sense resistor maximizes the differential input signal for a given amount of current flow and
reduces the error contribution of the offset voltage. However, there are practical limits as to how large the
current-sense resistor can be in a given application because of the resistor size and maximum allowable power
dissipation. Equation 1 gives the maximum value for the current-sense resistor for a given power dissipation
budget:
PDMAX
RSENSE
IMAX2
where:
•
•
PDMAX is the maximum allowable power dissipation in RSENSE.
IMAX is the maximum current that will flow through RSENSE.
(1)
An additional limitation on the size of the current-sense resistor and device gain is due to the power-supply
voltage, VS, and device swing-to-rail limitations. To make sure that the current-sense signal is properly passed to
the output, both positive and negative output swing limitations must be examined. Equation 2 provides the
maximum values of RSENSE and GAIN to keep the device from exceeding the positive swing limitation.
IMAX ª RSENSE ª *$,1 < VSP
where:
•
•
•
IMAX is the maximum current that will flow through RSENSE.
GAIN is the gain of the current-sense amplifier.
VSP is the positive output swing as specified in the data sheet.
(2)
To avoid positive output swing limitations when selecting the value of RSENSE, there is always a trade-off between
the value of the sense resistor and the gain of the device under consideration. If the sense resistor selected for
the maximum power dissipation is too large, then it is possible to select a lower-gain device to avoid positive
swing limitations.
The negative swing limitation places a limit on how small the sense resistor value can be for a given application.
Equation 3 provides the limit on the minimum value of the sense resistor.
IMIN ª RSENSE ª *$,1 > VSN
where:
•
•
•
IMIN is the minimum current that will flow through RSENSE.
GAIN is the gain of the current-sense amplifier.
VSN is the negative output swing of the device.
(3)
Table 3 shows an example of the different results obtained from using five different gain versions of the INA281.
From the table data, the highest gain device allows a smaller current-shunt resistor and decreased power
dissipation in the element.
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Application Information (continued)
Table 3. RSENSE Selection and Power Dissipation (1)
RESULTS AT VS = 5 V
PARAMETER
EQUATION
A1, B1
DEVICES
G
Gain
VDIFF
Ideal differential input voltage
VDIFF = VOUT / G
RSENSE
Current sense resistor value
RSENSE = VDIFF / IMAX
PSENSE
Current-sense resistor power dissipation
RSENSE × IMAX2
(1)
A2, B2
DEVICES
A3, B3
DEVICES
A4, B4
DEVICES
A5, B5
DEVICES
20 V/V
50 V/V
100 V/V
200 V/V
500 V/V
250 mV
100 mV
50 mV
25 mV
10 mV
25 mΩ
10 mΩ
5 mΩ
2.5 mΩ
1 mΩ
2.5 W
1W
0.5W
0.25 W
0.1 W
Design example with 10-A full-scale current with maximum output voltage set to 5 V.
8.1.2 Input Filtering
NOTE
Input filters are not required for accurate measurements using the INA281, and use of
filters in this location is not recommended. If filter components are used on the input of the
amplifier, follow the guidelines in this section to minimize the effects on performance.
Based strictly on user design requirements, external filtering of the current signal may be desired. The initial
location that can be considered for the filter is at the output of the current-sense amplifier. Although placing the
filter at the output satisfies the filtering requirements, this location changes the low output impedance measured
by any circuitry connected to the output voltage pin. The other location for filter placement is at the current-sense
amplifier input pins. This location also satisfies the filtering requirement, but the components must be carefully
selected to minimally impact device performance. Figure 29 shows a filter placed at the input pins.
VS
VCM
f3dB =
1
4ŒRINCIN
ISENSE
RIN
R1
IN+
+
CIN
RSENSE
Bias
RIN
R1
IN±
Current
Feedback
OUT
-
Load
Buffer
RL
GND
Figure 29. Filter at Input Pins
External series resistance provides a source of additional measurement error, so keep the value of these series
resistors to 10 Ω or less to reduce loss of accuracy. The internal bias network shown in Figure 29 creates a
mismatch in input bias currents (see Figure 7, Figure 8, and Figure 9) when a differential voltage is applied
between the input pins. If additional external series filter resistors are added to the circuit, a mismatch is created
in the voltage drop across the filter resistors. This voltage is a differential error voltage in the shunt resistor
voltage. In addition to the absolute resistor value, mismatch resulting from resistor tolerance can significantly
impact the error because this value is calculated based on the actual measured resistance.
The measurement error expected from the additional external filter resistors can be calculated using Equation 4,
and the gain error factor is calculated using Equation 5.
Gain Error (%) = 100 - (100 ´ Gain Error Factor)
(4)
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The gain error factor, shown in Equation 4, can be calculated to determine the gain error introduced by the
additional external series resistance. Equation 4 calculates the deviation of the shunt voltage, resulting from the
attenuation and imbalance created by the added external filter resistance. Table 4 provides the gain error factor
and gain error for several resistor values.
Gain Error Factor =
RB × R1
(RB × R1) + (RB × RIN) + (2 × RIN × R1)
Where:
•
•
•
RIN is the external filter resistance value.
R1 is the INA281 input resistance value specified in Table 1.
RB in the internal bias resistance, which is 6600 Ω ± 20%.
(5)
Table 4. Example Gain Error Factor and Gain Error for 10-Ω External Filter Input Resistors
DEVICE (GAIN)
GAIN ERROR FACTOR
GAIN ERROR (%)
A1 devices (20)
0.99658
–0.34185
A2 devices (50)
0.99598
–0.40141
A3 devices (100)
0.99598
–0.40141
A4 devices (200)
0.99499
–0.50051
A5 devices (500)
0.99203
–0.79663
8.2 Typical Application
The INA281 is a unidirectional, current-sense amplifier capable of measuring currents through a resistive shunt
with shunt common-mode voltages from –4 V to +110 V.
24 V
Solenoid
RSENSE
ISENSE
MCU
±
+
ADC
INA
5V
GND
Figure 30. Current Sensing in a Solenoid Application
8.2.1 Design Requirements
In this example application, the common-mode voltage ranges from 0 V to 24 V. The maximum sense current is
1.5 A, and a 5-V supply is available for the INA281. Following the design guidelines from RSENSE and Device
Gain Selection, a RSENSE of 50 mΩ and a gain of 50 V/V are selected to provide good output dynamic range.
Table 5 lists the design setup for this application.
Table 5. Design Parameters
DESIGN PARAMETERS
16
EXAMPLE VALUE
Power supply voltage
5V
Common mode voltage range
0 V to 24 V
Maximum sense current
1.5 A
RSENSE resistor
50 mΩ
Gain option
50 V/V
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8.2.2 Detailed Design Procedure
The INA281 is designed to measure current in a typical solenoid application. The INA281 measures current
across the 50-mΩ shunt that is placed at the output of the half-bridge. The INA281 measures the differential
voltage across the shunt resistor, and the signal is internally amplified with a gain of 50 V/V. The output of the
INA281 is connected to the analog-to-digital converter (ADC) of an MCU to digitize the current measurements.
Solenoid loads are highly inductive and are often prone to failure. Solenoids are often used for position control,
precise fluid control, and fluid regulation. Measuring real-time current on the solenoid continuously can indicate
premature failure of the solenoid which can lead to a faulty control loop in the system. Measuring high-side
current also indicates if there are any ground faults on the solenoid or the FETs that can be damaged in an
application. The INA281, with high bandwidth and slew rate, can be used to detect fast overcurrent conditions to
prevent the solenoid damage from short-to-ground faults.
8.2.2.1 Overload Recovery With Negative VSENSE
The INA281 is a unidirectional current-sense amplifier that is meant to operate with a positive differential input
voltage (VSENSE). If negative VSENSE is applied, the device is placed in an overload condition and requires time to
recover once VSENSE returns positive. The required overload recovery time increases with more negative VSENSE.
8.2.3 Application Curve
6
VCM
VOUT
4
Common-Mode Input Voltage, VCM (V)
2
40
0
Output Voltage, VOUT (V)
Figure 31 shows the output response of a solenoid.
30
20
10
0
Time (50 ms/div)
Figure 31. Solenoid Control Current Response
9 Power Supply Recommendations
The INA281 power supply can be 5 V, whereas the input common-mode voltage can vary between –4 V to 110
V. The output voltage range of the OUT pin, however, is limited by the voltage on the power-supply pin.
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10 Layout
10.1 Layout Guidelines
Attention to good layout practices is always recommended.
• Connect the input pins to the sensing resistor using a Kelvin or 4-wire connection. This connection technique
makes sure that only the current-sensing resistor impedance is detected between the input pins. Poor routing
of the current-sensing resistor commonly results in additional resistance present between the input pins.
Given the very low ohmic value of the current resistor, any additional high-current carrying impedance can
cause significant measurement errors.
• Place the power-supply bypass capacitor as close as possible to the device power supply and ground pins.
The recommended value of this bypass capacitor is 0.1 µF. Additional decoupling capacitance can be added
to compensate for noisy or high-impedance power supplies.
10.2 Layout Example
OUT
Supply
Voltage
Vs
Bypass
Cap
Via to GND Plane
GND
Ground Plane
IN +
IN -
Figure 32. INA281A Recommended Layout
OUT
IN -
Via to GND Plane
GND
Supply
Voltage
Vs
IN +
Bypass
Cap
Ground Plane
Figure 33. INA281B Recommended Layout
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
For related documentation see the following: Texas Instruments, INA281EVM user's guide
11.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
11.3 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
INA281A1IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B3C
INA281A1IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B3C
INA281A2IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B4C
INA281A2IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B4C
INA281A3IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B5C
INA281A3IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B5C
INA281A4IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B6C
INA281A4IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B6C
INA281A5IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B7C
INA281A5IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B7C
INA281B1IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B8C
INA281B1IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B8C
INA281B2IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B9C
INA281B2IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2B9C
INA281B3IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2BAC
INA281B3IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2BAC
INA281B4IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2BBC
INA281B4IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2BBC
INA281B5IDBVR
ACTIVE
SOT-23
DBV
5
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2BCC
INA281B5IDBVT
ACTIVE
SOT-23
DBV
5
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
2BCC
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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