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INA138, INA168
SBOS122E – DECEMBER 1999 – REVISED DECEMBER 2017
INA1x8 High-Side Measurement Current Shunt Monitor
1 Features
3 Description
•
The INA138 and INA168 (INA1x8) are high-side,
unipolar, current shunt monitors. Wide input commonmode voltage range, low quiescent current, and tiny
SOT-23 packaging enable use in a variety of
applications.
1
•
•
•
•
•
•
•
•
Complete Unipolar High-Side Current
Measurement Circuit
Wide Supply and Common-Mode Range
INA138: 2.7 V to 36 V
INA168: 2.7 V to 60 V
Independent Supply and Input Common-Mode
Voltages
Single Resistor Gain Set
Low Quiescent Current (25 µA Typical)
Wide Temperature Range: –40°C to +125°C
5-Pin SOT-23 Package
Input common-mode and power-supply voltages are
independent and can range from 2.7 V to 36 V for the
INA138 and 2.7 V to 60 V for the INA168. Quiescent
current is only 25 µA, which permits connecting the
power supply to either side of the current
measurement shunt with minimal error.
The device converts a differential input voltage to a
current output. This current is converted back to a
voltage with an external load resistor that sets any
gain from 1 to over 100. Although designed for
current shunt measurement, the circuit invites
creative applications in measurement and level
shifting.
2 Applications
•
•
•
•
•
•
Current Shunt Measurement:
– Telephone, Computers
Portable and Battery-Backup Systems
Battery Chargers
Power Management
Cell Phones
Precision Current Source
Both the INA138 and INA168 are available in SOT235 and are specified for the –40°C to 125°C
temperature range.
Device Information(1)
PART NUMBER
INA138
INA168
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 datasheet.
Typical Application Circuit
IS
RS
VIN+
Up To 60 V
3
4
VIN–
VIN+
5 kΩ
Load
5 kΩ
V+
5
OUT
GND
1
VO = ISRSRL / 5 kΩ
2
Copyright © 1999, Texas Instruments Incorporated
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.
INA138, INA168
SBOS122E – DECEMBER 1999 – REVISED DECEMBER 2017
www.ti.com
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
4
6.1
6.2
6.3
6.4
6.5
6.6
4
4
4
5
5
6
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Information .................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description .............................................. 8
7.1
7.2
7.3
7.4
Overview ...................................................................
Functional Block Diagram .........................................
Feature Description...................................................
Device Functional Modes..........................................
8
8
9
9
8
Application and Implementation ........................ 10
8.1 Application Information............................................ 10
8.2 Typical Applications ............................................... 11
9 Power Supply Recommendations...................... 18
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
11.7
Documentation Support .......................................
Related Links ........................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
19
19
19
19
19
19
19
12 Mechanical, Packaging, and Orderable
Information ........................................................... 20
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (December 2014) to Revision E
Page
•
Added reference design link to navigation bar at the top of the front page ........................................................................... 1
•
Changed body size from 18.00 mm × 18.00 mm to 2.90 mm × 1.60 mm in Device Information table.................................. 1
•
Changed pin numbers in pin functions table to match pin configuration figure...................................................................... 3
•
Changed Absolute Maximum Ratings table for clarity; no values were changed ................................................................. 4
•
Changed Recommended Operating Conditions table; moved some content from Electrical Characteristics table, but
no values changed ................................................................................................................................................................. 4
•
Changed all values in Thermal Information table ................................................................................................................... 5
•
Changed Electrical Characteristics table; reformatted for clarity; moved some content to Recommended Operating
Conditions table, and deleted duplicate content..................................................................................................................... 5
•
Changed common-mode rejection test conditions to better highlight each device in Electrical Characteristics table .......... 5
•
Changed offset voltage vs temperature to offset voltage drift in Electrical Characteristics table........................................... 5
•
Changed offset voltage vs power supply test conditions to better highlight each device in Electrical Characteristics table . 5
•
Changed reference in text from Figure 10 to Figure 11 in last paragraph of Selecting the Shunt Resistor and RL section 12
Changes from Revision C (November 2005) to Revision D
•
2
Page
Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section. ................................................................................................ 1
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5 Pin Configuration and Functions
DBV Package
5-Pin SOT-23
Top View
OUT
1
GND
2
VIN+
3
5
V+
4
VIN±
Not to scale
Pin Functions
PIN
NO.
NAME
I/O
DESCRIPTION
1
OUT
O
Output current
2
GND
—
Ground
3
VIN+
I
Positive input voltage
4
VIN–
I
Negative input voltage
5
V+
I
Power supply voltage
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
INA138
Supply, V+
INA168
INA138
Voltage
(1)
Analog input, VIN+, VIN–
INA168
75
–0.3
60
Sense voltage, VSENSE = (VIN+ – VIN–)
–40
2
–0.3
75
Common mode
(2)
Sense voltage, VSENSE = (VIN+ – VIN–)
2
–0.3
40
–55
150
10
Junction, TJ
mA
150
Storage, Tstg
–65
UNIT
V
–40
Input current into any pin
Temperature
(2)
60
–0.3
Operating, TA
(1)
MAX
Common mode (2)
Analog output, OUT pin (2)
Current
MIN
–0.3
°C
150
Stresses beyond those listed under Absolute Maximum Ratings 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 Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
The input voltage at any pin may exceed the voltage shown if the current at that pin is limited to 10 mA.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001
(1)
±1000
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±500
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.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
NOM
MAX
UNIT
INA138
V+
Supply voltage
VSENSE
Full-scale sense voltage (VIN+ – VIN–)
2.7
5
36
V
100
500
mV
Common-mode voltage
2.7
12
36
V
Operating temperature
–40
25
125
°C
V+
Supply voltage
2.7
VSENSE
Full-scale sense voltage (VIN+ – VIN–)
TA
INA168
TA
4
5
60
V
100
500
mV
Common-mode voltage
2.7
12
60
V
Operating temperature
–40
25
125
°C
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6.4 Thermal Information
INA1x8
THERMAL METRIC (1)
DBV
UNIT
5 PINS
RθJA
Junction-to-ambient thermal resistance
168.3
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
73.8
°C/W
RθJB
Junction-to-board thermal resistance
28.1
°C/W
ψJT
Junction-to-top characterization parameter
2.5
°C/W
ψJB
Junction-to-board characterization parameter
27.6
°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
all other characteristics at TA = +25°C, VS = 5 V, VIN+ = 12 V, and ROUT = 125 kΩ (unless otherwise noted)
PARAMETER
TEST CONDITIONS
INA1x8
MIN
TYP
INA138, VIN+ = 2.7 V to 36 V
100
120
INA168, VIN+ = 2.7 V to 60 V
100
120
MAX
UNIT
INPUT
Common-mode rejection
Offset voltage (1)
Offset voltage drift (1)
Offset voltage vs power supply, V+
Input bias current
VSENSE = 50 mV
TA = 25°C
±0.2
TA = –40°C to +125°C
±1
mV
±2
TA = –40°C to +125°C
VSENSE = 50 mV
dB
1
µV/°C
INA138, V+ = 2.7 V to 36 V
0.1
10
INA168, V+ = 2.7 V to 60 V
0.1
10
TA = 25°C
µV/V
2
TA = –40°C to +125°C, INA138
µA
10
OUTPUT
Transconductance
VSENSE = 10 mV to 150 mV, TA = 25°C
198
VSENSE = 100 mV, TA = –40°C to +125°C
196
Transconductance drift
TA = –40°C to +125°C
Nonlinearity error
VSENSE = 10 mV to 150 mV
Total output error
VSENSE = 100 mV
202
204
10
µA/V
µA/V
nA/°C
±0.01%
±0.1%
TA = 25°C
±0.5%
±2%
TA = –40°C to +125°C
±2.5%
Output impedance
Voltage output swing
200
1 || 5
GΩ || pF
To power supply voltage, V+
(V+) – 0.8
(V+) – 1.0
V
To common-mode voltage, VCM
VCM – 0.5
VCM – 0.8
V
FREQUENCY RESPONSE
Bandwidth
Settling time
ROUT = 5 kΩ
800
kHz
32
kHz
5-V step, ROUT = 5 kΩ
1.8
µs
5-V step, ROUT = 125 kΩ
30
µs
9
pA/√Hz
3
nA RMS
ROUT = 125 kΩ
To 0.1%
NOISE
Output-current noise density
Total output-current noise
BW = 100 kHz
POWER SUPPLY
Quiescent current
(1)
VSENSE = 0 V,
IO = 0 mA
TA = 25°C
TA = –40°C to +125°C
25
45
µA
60
µA
Defined as the amount of input voltage, VSENSE, to drive the output to zero.
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6.6 Typical Characteristics
At TA = +25°C, V+ = 5 V, VIN+ = 12 V, and RL = 125 kΩ, unless otherwise noted.
40
120
Common-Mode Rejection (dB)
RL = 500kΩ
30
RL = 50kΩ
Gain (dB)
20
10
RL = 5kΩ
0
–10
CL = 10nF
–20
100
1k
CL = 1nF
10k
CL = 100pF
100k
1M
G = 100
100
80
G = 10
60
G=1
40
20
0
10M
0.1
Frequency (Hz)
1
10
100
1k
10k
100k
Frequency (Hz)
Figure 1. Gain vs Frequency
Figure 2. Common-Mode Rejection vs Frequency
140
5
VIN = (VIN+ – VIN–)
G = 100
100
G = 10
80
G=1
60
Total Output Error (%)
Power-Supply Rejection (dB)
–55°C
120
0
+150°C
–5
+25°C
–10
40
–15
20
1
10
100
1k
Frequency (Hz)
10k
0
100k
25
100
125
150
200
Figure 4. Total Output Error vs VIN
2
50
Output error is essentially
independent of both
V+ supply voltage and
input common-mode voltage.
1
G=1
0
G = 10
G = 25
–1
+150°
40
Quiescent Current (µA)
Total Output Error (%)
75
VIN (mV)
Figure 3. Power-Supply Rejection vs Frequency
–2
+125°
30
+25°
–55°
20
Use INA168 with
(V+) > 36V
10
0
0
10
20
30
40
50
60
70
0
10
Power-Supply Voltage (V)
20
30
40
50
60
70
Power-Supply Voltage (V)
Figure 5. Total Output Error vs Power-Supply Voltage
6
50
Figure 6. Quiescent Current vs Power-Supply Voltage
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Typical Characteristics (continued)
At TA = +25°C, V+ = 5 V, VIN+ = 12 V, and RL = 125 kΩ, unless otherwise noted.
m
m
Figure 8. Step Response
Figure 7. Step Response
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7 Detailed Description
7.1 Overview
The INA138 and INA168 devices (INA1x8) are comprised of a high voltage, precision operational amplifier,
precision thin film resistors trimmed in production to an absolute tolerance and a low noise output transistor. The
INA1x8 devices can be powered from a single power supply and their input voltages can exceed the power
supply voltage. The INA1x8 devices are ideal for measuring small differential voltages, such as those generated
across a shunt resistor, in the presence of large common-mode voltages. Refer to Functional Block Diagram
which illustrates the functional components within both INA1x8 devices.
7.2 Functional Block Diagram
VIN+
VIN–
V+
OUT
GND
8
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7.3 Feature Description
7.3.1 Output Voltage Range
The output of the INA1x8 device is a current that is converted to a voltage by the load resistor, RL. The output
current remains accurate within the compliance voltage range of the output circuitry. The shunt voltage and the
input common-mode and power-supply voltages limit the maximum possible output swing. The maximum output
voltage (Vout max) compliance is limited by either Equation 1 or Equation 2, whichever is lower:
Vout max = (V+) – 0.7 V – (VIN+ – VIN–)
(1)
Vout max = VIN– – 0.5 V
(2)
or
7.3.2 Bandwidth
Measurement bandwidth is affected by the value of the load resistor, RL. High gain produced by high values of
RL will yield a narrower measurement bandwidth (see Typical Characteristics). For widest possible bandwidth,
keep the capacitive load on the output to a minimum. Reduction in bandwidth due to capacitive load is shown in
the Typical Characteristics.
If bandwidth limiting (filtering) is desired, a capacitor can be added to the output (see Figure 12). This will not
cause instability.
7.4 Device Functional Modes
For proper operation the INA1x8 devices must operate within their specified limits. Operating either device
outside of their specified power supply voltage range or their specified common-mode range will result in
unexpected behavior and is not recommended. Additionally operating the output beyond their specified limits with
respect to power supply voltage and input common-mode voltage will also produce unexpected results. Refer to
Electrical Characteristics for the device specifications.
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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
8.1.1 Operation
Figure 9 illustrates the basic circuit diagram for both the INA138 and INA168 devices. Load current IS is drawn
from supply VS through shunt resistor RS. The voltage drop in shunt resistor VS is forced across RG1 by the
internal op amp, causing current to flow into the collector of Q1. External resistor RL converts the output current
to a voltage, VOUT, at the OUT pin. The transfer function for the INA138 device is:
IO = gm(VIN+ – VIN–)
(3)
where gm = 200 µA/V.
In the circuit of Figure 9, the input voltage, (VIN+ – VIN–), is equal to IS × RS and the output voltage, VOUT, is equal
to IO × RL. The transconductance, gm, of the INA138 device is 200 µA/V. The complete transfer function for the
current measurement amplifier in this application is:
VOUT = (IS) (RS) (200 µA/V) (RL)
(4)
The maximum differential input voltage for accurate measurements is 0.5 V, which produces a 100-µA output
current. A differential input voltage of up to 2 V will not cause damage. Differential measurements (pins 3 and 4)
must be unipolar with a more-positive voltage applied to pin 3. If a more-negative voltage is applied to pin 3, the
output current, IO, will be zero, but it will not cause damage.
VP
Load Power Supply
2.7 V to 36 V(1)
Shunt
RS
VIN–
VIN+
3
V+ power can be common or
V+
independent of load supply.
4
RG1
5 kΩ
2.7 V ≤ (V+) ≤ 36 V(1)
IS
Load
RG2
5 kΩ
5
Q1
(1)
VOLTAGE GAIN
EXACT RL (Ω)
NEAREST 1% RL (Ω)
1
5k
4.99k
2
10k
10k
5
25k
24.9k
10
50k
49.9k
20
100k
100k
50
250k
249k
100
500k
499k
INA138
2
OUT
1
+
I0
RL
VO
–
Copyright © 1999, Texas Instruments Incorporated
Maximum VP and V+ voltage is 60 V with INA168.
Figure 9. Basic Circuit Connections
10
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8.2 Typical Applications
The INA1x8 devices are designed for current shunt measurement circuits, as shown in Figure 9, but basic device
function is useful in a wide range of circuitry. A creative engineer will find many unforeseen uses in measurement
and level-shifting circuits. A few ideas are illustrated in Figure 10 through Figure 18.
8.2.1 Buffering Output to Drive an ADC
IS
VIN+
VIN-
OPA340
+
INA138
or
INA168
RS
ADC
RL
Buffer amplifier
drives ADC without
affecting gain
C
Figure 10. Buffering Output to Drive an ADC
8.2.1.1 Design Requirements
Digitize the output of the INA1x8 devices using a 1-MSPS analog-to-digital converter (ADC).
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Selecting the Shunt Resistor and RL
In Figure 9 the value chosen for the shunt resistor depends on the application and is a compromise between
small-signal accuracy and maximum permissible voltage loss in the measurement line. High values of shunt
resistor provide better accuracy at lower currents by minimizing the effects of offset, while low values of shunt
resistor minimize voltage loss in the supply line. For most applications, best performance is attained with a shunt
resistor value that provides a full-scale shunt voltage range of 50 mV to 100 mV. Maximum input voltage for
accurate measurements is 500 mV.
The load resistor, RL, is chosen to provide the desired full-scale output voltage. The output impedance of the
INA1x8 OUT terminal is very high which permits using values of RL up to 500 kΩ with excellent accuracy. The
input impedance of any additional circuitry at the output should be much higher than the value of RL to avoid
degrading accuracy.
Some analog-to-digital converters (ADCs) have input impedances that significantly affect measurement gain. The
input impedance of the ADC can be included as part of the effective RL if its input can be modeled as a resistor
to ground. Alternatively, an op amp can be used to buffer the ADC input. The INA1x8 are current output devices,
and as such have an inherently large output impedance. The output currents from the amplifier are converted to
an output voltage via the load resistor, RL, connected from the amplifier output to ground. The ratio of the load
resistor value to that of the internal resistor value determines the voltage gain of the system.
In many applications digitizing the output of the INA1x8 device is required, and can be accomplished by
connecting the output of the amplifier to an ADC. It is very common for an ADC to have a dynamic input
impedance. If the INA1x8 output is connected directly to an ADC input, the input impedance of the ADC is
effectively connected in parallel with the gain setting resistor RL. This parallel impedance combination will affect
the gain of the system and the impact on the gain is difficult to estimate accurately. A simple solution that
eliminates the paralleling of impedances, simplifying the gain of the circuit is to place a buffer amplifier, such as
the OPA340, between the output of the INA138 or INA168 device and the input to the ADC.
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Typical Applications (continued)
Figure 10 illustrates this concept. Notice that a low pass filter is placed between the OPA340 output and the input
to the ADC. The filter capacitor is required to provide any instantaneous demand for current required by the input
stage of the ADC. The filter resistor is required to isolate the OPA340 output from the filter capacitor to maintain
circuit stability. The values for the filter components will vary according to the operational amplifier used for the
buffer and the particular ADC selected. More information can be found regarding the design of the low pass filter
in the TI Precision Design , 16 bit 1MSPS Data Acquisition Reference Design for Single-Ended Multiplexed
Applications (TIPD173).
Figure 11 shows the expected results when driving an analog-to-digital converter at 1MSPS with and without
buffering the INA1x8 output. Without the buffer, the high impedance of the INA1x8 reacts with the input
capacitance and sample and hold (S/H) capacitance of the ADC, and does not allow the S/H to reach the correct
final value before it is reset and the next conversion starts. Adding the buffer amplifier significantly reduces the
output impedance driving the S/H and allows for higher conversion rates than can be achieved without adding
the buffer.
8.2.1.3 Application Curve
Input to ADC (0.25 V/div)
with buffer
without Buffer
Time
Figure 11. Driving an ADC With and Without a Buffer
12
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Typical Applications (continued)
8.2.2 Output Filter
3
4
f–3dB
1
f–3dB =
2 πR L C L
INA138
VO
RL
CL
Figure 12. Output Filter
8.2.2.1 Design Requirements
Filter the output of the INA1x8 devices.
8.2.2.2 Detailed Design Procedure
A low-pass filter can be formed at the output of the INA1x8 devices simply by placing a capacitor of the desired
value in parallel with the load resistor. First determine the value of the load resistor needed to achieve the
desired gain. Refer to the table in Figure 9. Next, determine the capacitor value that will result in the desired
cutoff frequency according to the equation shown in Figure 12. Figure 13 illustrates various combinations of gain
settings (determined by RL) and filter capacitors.
8.2.2.3 Application Curve
40
RL = 500kΩ
30
RL = 50kΩ
Gain (dB)
20
10
0
RL = 5kΩ
–10
CL = 10nF
–20
100
1k
10k
CL = 1nF
100k
CL = 100pF
1M
10M
Frequency (Hz)
Figure 13. Gain vs Frequency
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Typical Applications (continued)
8.2.3 Offsetting the Output Voltage
For many applications using only a single power supply it may be required to level shift the output voltage away
from ground when there is no load current flowing in the shunt resistor. Level shifting the output of the INA1x8
devices is easily accomplished by one of two simple methods shown in Figure 14. The method on the left hand
side of Figure 14 illustrates a simple voltage divider method. This method is useful for applications that require
the output of the INA1x8 devices to remain centered with respect to the power supply at zero load current
through the shunt resistor. Using this method the gain is determine by the parallel combination of R1 and R2
while the output offset is determined by the voltage divider ratio R1 and R2. For applications that may require a
fixed value of output offset, independent of the power supply voltage, the current source method shown on the
right-hand side of Figure 14 is recommended. With this method a REF200 constant current source is used to
generate a constant output offset. Using his method the gain is determined by RL and the offset is determined by
the product of the value of the current source and RL.
3
VR
4
3
R1
INA138
V+
4
REF200
100 µA
INA138
VO
VO
1
1
R2
Gain Set by R1 || R2
Output Offset =
RL
Gain Set by RL
Output Offset = (100 µA)(RL)
(independent of V+)
(VR)R2
R1 + R2
a) Using resistor divider.
b) Using current source.
Figure 14. Offsetting the Output Voltage
14
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Typical Applications (continued)
8.2.4 Bipolar Current Measurement
The INA1x8 devices can be configured as shown in Figure 15 in applications where measuring current bidirectionally is required. Two INA devices are required connecting their inputs across the shunt resistor as shown
in Figure 15. A comparator, such as the TLV3201, is used to detect the polarity of the load current. The
magnitude of the load current is monitored across the resistor connected between ground and the connection
labeled Output. In this example the 100-kΩ resistor results in a gain of 20 V/V. The 10-kΩ resistors connected in
series with the INA1x8 output current are used to develop a voltage across the comparator inputs. Two diodes
are required to prevent current flow into the INA1x8 output, as only one device at a time is providing current to
the Output connection of the circuit. The circuit functionality is illustrated in Figure 16.
±1 A
Load Curent
RSH
100 m
VIN+
VIN±
VIN±
VIN+
Bus
Voltage
Load
Current
5k
5k
5k
V+
+
INA138
or
INA168
+5 V
V+
+
+5 V
5k
OUT
OUT
GND
GND
1N4148
INA138
or
INA168
1N4148
+
Sign
TLV3201
10 k
10 k
Output
100 k
Figure 15. Bipolar Current Measurement
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Typical Applications (continued)
Voltage
Load Current
Output
Sign
Time
Figure 16. Bipolar Current Measurements Results (arbitrary scale)
8.2.5 Bipolar Current Measurement Using Differential Input of ADC
The INA1x8 devices can be used with an ADC such as the ADS7870 programmed for differential mode
operation. Figure 17 illustrates this configuration. In this configuration the use of two INAs allows for bidirectional
current measurement. Depending upon the polarity of the current, one of the INAs provides an output voltage,
while the other output is zero. In this way the ADC reads the polarity of current directly, without the need for
additional circuitry.
RS
V+
4
3
4
3
+5V
+5V
+5V
5
REFOUT BUFIN
BUFOUT
5
Digital
I/O
INA138
2
1
RL
25kΩ
REF
BUF
INA138
2
1
MUX
PGIA
12-Bit A/D
Converter
RL
25kΩ
A/D converter programmed for differential input.
Depending on polarity of current, one INA138 provides
an output voltage, the output of the other is zero.
Clock
Divider
Oscillator
ADS7870
Serial
I/O
Figure 17. Bipolar Current Measurement Using Differential Input of ADC
16
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Typical Applications (continued)
8.2.6 Multiplexed Measurement Using Logic Signal for Power
Multiple loads can be measured as illustrated in Figure 18. In this configuration each INA1x8 device is powered
by the digital I/O from the ADS7870. Multiplexing is achieved by switching on or off each the desired I/O.
Other INA168s
Digital I/O on the ADS7870 provides power to select
the desired INA168. Diodes prevent output current of
the on INA168 from flowing into the off INA168.
INA168
V+
+5V
––
REFOUT BUFIN
Digital
I/O
REF
BUFOUT
BUF
INA168
V+
––
MUX
12-Bit A/D
Converter
PGIA
IN4148
RL
Clock
Divider
Oscillator
Serial
I/O
ADS7870
Figure 18. Multiplexed Measurement Using Logic Signal for Power
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9 Power Supply Recommendations
The input circuitry of the INA138 can accurately measure beyond its power-supply voltage, V+. For example, the
V+ power supply can be 5 V, whereas the load power supply voltage is up to 36 V (or 60 V with the INA168).
The output voltage range of the OUT terminal, however, is limited by the lesser of the two voltages (see Output
Voltage Range). A 0.1-µF capacitor is recommenced to be placed near the power supply pin on the INA138 or
INA168. Additional capacitance may be required for applications with noisy power supply voltages.
10 Layout
10.1 Layout Guidelines
Figure 19 shows the basic connection of the INA138 device. The input pins, VIN+ and VIN– , should be connected
as closely as possible to the shunt resistor to minimize any resistance in series with the shunt resistance. The
output resistor, RL, is shown connected between pin 1 and ground. Best accuracy is achieved with the output
voltage measured directly across RL. This is especially important in high-current systems where load current
could flow in the ground connections, affecting the measurement accuracy.
No power-supply bypass capacitors are required for stability of the INA138. However, applications with noisy or
high-impedance power supplies may require decoupling capacitors to reject power-supply noise. Connect bypass
capacitors close to the device pins.
10.2 Layout Example
VIA to Ground Plane
INA138
INA168
Output
OUT
Supply Voltage
V+
0.1 µF
GND
RL
To Bus
Voltage
VIN+
VIN-
PCB pad
To Load
PCB pad
RSHUNT
Figure 19. Typical Layout Example
18
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
For related documentation see the following:
• 16 bit 1MSPS Data Acquisition Reference Design for Single-Ended Multiplexed Applications
• ADS7870 12-Bit ADC, MUX, PGA and Internal Reference Data Acquisition System
• TLV3201, TLV3202 40-ns, microPOWER, Push-Pull Output Comparators
• REF200 Dual Current Source/Current Sink
11.2 Related Links
Table 1 lists quick access links. Categories include technical documents, support and community resources,
tools and software, and quick access to sample or buy.
Table 1. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
INA138
Click here
Click here
Click here
Click here
Click here
INA168
Click here
Click here
Click here
Click here
Click here
11.3 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.
11.4 Community Resources
The following links connect to TI community resources. Linked contents are 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.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.5 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.6 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.
11.7 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
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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.
20
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PACKAGE OPTION ADDENDUM
www.ti.com
26-Aug-2017
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
INA138NA/250
ACTIVE
SOT-23
DBV
5
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 125
B38
INA138NA/3KG4
ACTIVE
SOT-23
DBV
5
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 125
B38
INA168NA/250
ACTIVE
SOT-23
DBV
5
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
INA168NA/3K
ACTIVE
SOT-23
DBV
5
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
A68
-40 to 125
A68
(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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