Current Shunt Monitors (Rev. A) TEXAS MONITOR GUIDE
User Manual:
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2014www.ti.com/currentshuntmonitor
Current Shunt Monitors
Load
High-Side
Sensing
Power
Supply
Low-Side
Sensing
VOUT
VOUT
Current
Shunt
Current Shunt Monitors
Current Shunt Monitors Texas Instruments 2014
•
Current shunt monitors are also
referred to as current sense amplifiers.
•
Current shunt monitors are designed
to monitor the current flow by
measuring the voltage drop across a
resistor placed in the current path.
•
Current sense amplifiers tend to be
easier to design, more precise, less
prone to noise and lower cost than
magnetic current sensors.
Current to be
measured
Current to be
measured
RSHUNT Voltmeter
V
Common Mode Range:
This specification defines the DC
voltage range at the input of an
amplifier with respect to ground.
Current shunt monitors are typically
designed to accept common mode
voltages well beyond the chip supply
voltage. For example, the INA282
is capable of accepting a common
mode voltage from -14V to +80V while
running on a supply as low as 2.7V.
Offset Voltage:
The differential DC error at the input
of the amplifier. Historically, to reduce
the impact of amplifiers with high
offsets, larger shunt resistors are used
to increase the measured voltage
drop. Today, TI is able to offer current
sensing solutions with offsets as low
as 10µV, enabling higher precision
measurements at low currents and the
use of smaller shunt resistances for
improved system efficiency.
CMRR
(Common Mode Rejection Ratio):
CMRR is the ability of the amplifier
to reject signals common to the
differential inputs. This is important
in the ability to measure small signals
superimposed upon a large voltage.
TI’s portfolio offers solutions with
CMRR as high as 140dB.
Digital Output: Simple all-in-one solution integrating the
ADC/MUX with programmable switching. Provides
measurements in amps, volts and watts across the I2C
interface for a complete power monitoring solution.
GND
VBUS
V
I
VIN+
VIN
I C
Interface
2
SDA
SCL
A0
A1
Alert Register
Alert
Voltage Register
Current Register
ADC
Power Register
VREF
VOUT
VIN+
VIN-
Voltage Output: High precision, lowest power and
industry’s smallest form factors. Fixed gain options
ranging from 14V/V to 1000V/V. Variable gain may be
set through an external resistor.
Current Output: Variable gain set through
external resistor. Highest bandwidth options.
VOUT
VIN+
VIN-
2
Output Types
Key Parameters
What are Current Shunt Monitors?
Current Shunt Monitors Texas Instruments 2014
LOAD
–5V
+5V
+5V
I2C
FS = 0.2V
G = 4
3kΩ
1kΩ
RS
50mV
Shunt
RPD
(1)
49 .9 kΩ
OPA335
ADS1114
-
+
Power
Supply
PGA Gain = 16
256V FS
Note: (1) Pull-down resistor to
allow accurate swing to OV.
Advantages:
• Typically only requires an op amp
such as OPA335
• Straightforward, easy
• Inexpensive
Disadvantages:
• Undesirable resistance in the load’s
ground path
• Cannot detect fault conditions
(short/open circuits)
• Requires precision external
components to achieve and
maintain high accuracy
Advantages over op amps as a
low-side monitor:
• Integrated gain resistors
• Excellent matching that requires
more expensive external precision
resistors with an op amp approach
• Integrated resistors approach
reduces board space requirements
Disadvantages over op amps:
• Fixed gain settings reduce flexibility
in maximizing the full-scale range of
the following ADC stage
Low-side current sensing techniques connect the current sense element
between the load and ground.
When to choose low-side sensing: Always choose low-side sensing if the
system can tolerate disturbances on the ground path.
High-side monitors are designed
to accommodate input voltages
that exceed the power supply
voltage. However, many of our
current shunt monitors have
common-mode ranges that include
or even go below ground. This
makes them excellent low-side
current shunt monitors as well.
Advantages:
• Eliminates ground disturbances
associated with low-side sensing
• Able to detect fault conditions
Disadvantages:
• Difficult to use standard op amp.
Resistors must be precisely matched
to obtain acceptable common mode
rejection ratios (CMRR)
• A 0.01% deviation in resistor
value lowers the CMRR to 86dB
approach
• A 0.1% deviation in resistor value
lowers the CMRR to 66dB
• A 1% deviation in resistor value
lowers the CMRR to 46dB
• Must withstand very high, dynamic
changes in common mode voltage
High-side current sensing techniques connect the current sense element
between the supply and the load.
When to choose high-side sensing:
• System cannot tolerate ground disturbance of low side sensing
• System needs to be able to identify shorts to ground
LOAD
+5V
Power
Supply
I2C
RS
ADS1114
-
+
INA 210
+5V
High-Side
Sensing
3
High-Side Measurements
Low-Side Measurements With a High-Side Monitor
Current Shunt Monitors
Low-Side Measurements
LOAD
I2C
RS
20mV
Shunt
ADS1114
Power Supply
PGA Gain = 1
4.096V FS
INA210
-
+
+5V
Current Shunt Monitors Texas Instruments 2014
Current Shunt Monitors
4
• For small differential signals at the
input, the error is dominated by the
amplifier’s offset voltage. Low input
offsets are critical to achieving
accurate measurements at the low
end of the dynamic range.
• For large differential signals at the
input, the error is dominated by the
amplifier’s gain error.
0%
2%
4%
6%
8%
10%
0 10 20 30 40 50 60 70 80 90 100
Total Error %
Differential Voltage (mV)
Total Error vs. Differential Input Voltage
10µV; 0.1%
10µV; 1%
1mV; 1%
1mV; 5%
Offset; Gain Error
Extending the Common Mode Range
Example 1: MOSFET and Zener
GND
V+
VIN -
V
DZ1
39V
zener
Q1
BSS92
OUT
1
5
2
3 4
R
0.1Ω
S
VIN +
RL
Supply
+160 to
+200V
R1
330kΩ
C1
0.1µF
5kΩ 5kΩ
OUT
50kΩ
(1V at 1A)
IC1 INA168
(200 µA/V)
Load
Up to 1A
+ -
Intermediate
Power Bus
LMP92064
RSENSE
VIN
SPI Bus
GND
VDD
–48V
SPI Bus
INCP
INCN
INVG
INVP
System
Management
Controller
Digital
Isolators
Isolated
Power
Converter
Example 3: Isolated SPI Interface Example 4: Isolated I2C Interface
Example 2: Current Follower
With additional circuitry, current shunts can be configured to operate beyond the specified common mode range by
using one of the following techniques.
Total Error
From
Supply Load
10kΩ
Data
(SDA)
Clock
(SCL)
Two-Wire
Interface
VIN+
ADC
INA220
GND
A0
A1
VIN-
VS (Supply Voltage)
VBUS
RG
10µF
0.1µF
+3.3V to +5V
V
I
OPA333
100Ω
35.7kΩ
13.7kΩ
Shunt
RSHUNT
5.1V
Zener
24V
Tranzorb
RL
Voltage Register
Current Register
Power Register
MOSFET rated to
standoff supply voltage
such as BSS84 for
up to 50V
(Bus Voltage Input)
100Ω
+5V Zener RZ
I2C I2C
ISO1541
–48V
RSENSE
I2C
System
Management
Controller
INA220
LOAD
VS
VBUS
V+
V–
GND
INA226: Highest precision solution on
the market
• Integrated ADC and MUX with
programmable sampling
• Common mode range = 0V to 36V
• Offset (max) = 10µV
• Gain error (max) = 0.1%
• CMRR (typ) = 140dB
• Lower cost alternative: INA219,
INA230
INA210: Precision voltage output
• Gain options: 50V/V, 100V/V,
200V/V, 500V/V, 1000V/V
• Common mode range: –0.3V to 26V
• Offset (max) = 35µV
• Gain error (max) = 1%
• CMRR (typ) = 140dB
• Lower cost alternative: INA199
INA216: Designed for portable battery
powered applications
• Gain options: 25V/V, 50V/V, 100V/V,
200V/V
• Common mode range = 1.8V to 5.5V
• Offset (max) = 75µV
• Gain error (max) = 0.2%
• Quiescent current = 25µA
• CMRR (typ) = 108dB
• 0.76 x 0.76mm WCSP or QFN
package available
INA3221: Triple-channel digital shunt
and bus voltage monitor
• Integrated ADC and MUX with
programmable sampling
• Common mode range = 0V to 26V
• Offset error (max) = 80µV
• Gain error (max): 0.5%
• Quiescent current = 450µA
INA282: Widest common mode
range + precision
• Common mode range = -14V to 80V
• Offset (max) = 70µV
• Offset drift (max) = 1.5µV/ºC
• Gain error (max) = 1.4%
• CMRR (typ) = 140dB
• Lower cost alternative: INA193,
LMP8601
LMP8640: High bandwidth and
high voltage
• Bandwidth = 950kHz
• Common mode range: -2V to 76V
• Offset (max) = 900µV
• Gain error = 0.25%
• CMRR (min) = 103dB
• Lower cost alternative: LMP8645
AMC1200: 4kV isolated amplifier
• Offset (max) = 1.5mV
• Offset drift (max) = 10µV/K
• Gain error (max) = 1%
• CMRR (typ) = 108dB
LMP8481: High voltage
• Bandwidth = 270kHz
• Common mode range = 4.0V to 76V
• Offset (max) = 400µV
• Gain error (max) = 1.2%
• CMRR (typ) = 124dB
• Lower cost alternative: LMP8480
LMP92064: Simultaneous sampling
current/voltage monitor
• 125ksamples/sec
• Bandwidth = 70kHz
• Offset (max) = 60µV
• Gain error (max) = 0.75%
Applications:
• Battery gauge:
(Coulomb Counting)
• Power supplies
• Inductive charging
• Graphics cards
• Desktops / laptops / servers
• Tablets / E-books
• Smartphones & feature phones
• Basestations
• Networking
• Industrial automation
• Automotive
• Medical
• Motor control
• Battery backups
• Inverters
• Solar
INA225: Programmable gain,
zero-drift current sense amplifier
• 4-pin selectable gain settings
• Bandwidth = 100kHz @ 100V/V
• Offset (max) = 125µV
• Gain error (max) = 0.50%
INA300: Over current detector
• Input/output response time = 10µs
• Programmable threshold:
0 to 250mV
• Hysteresis of 2, 5, or 10mV
Current Shunt Monitors Texas Instruments 2014
Current Shunt Monitors
Featured Products
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