Texas Instruments | Common Uses for Multichannel Current Monitoring | Application notes | Texas Instruments Common Uses for Multichannel Current Monitoring Application notes

Texas Instruments Common Uses for Multichannel Current Monitoring Application notes
____________________________________________________
Common Uses for Multi-channel Current Monitoring
Dennis Hudgins, Current Sensing Products
As the need for system intelligence and power
efficiency continues to grow, the need for better
monitoring of critical system currents is increasingly
paramount. In the past this may have been done with
multiple operational amplifiers configured as difference
amplifiers or multiple current sense amplifiers
distributed within the system. As the number of current
monitor channels increases so does the amount of
external components needed to realize a solution. The
added components increase the design complexity
and solution size, and can degrade the overall current
sensing accuracy.
For example, consider the case where two currents
need to be measured as shown in Figure 1.
Power
Supply
allow use of a cheaper wider tolerance current sense
resistor. The INA2180 and INA2181 family are also
more flexible in that they can monitor voltage drops
across resistors that have voltages greater than the
supply voltage.
In addition to simplifying the design process and
reducing the number of external components, having
multiple current monitoring devices in a single package
facilities several common application solutions.
For example, consider the application shown in
Figure 2, where the total current drawn by the memory
and processor is monitored by an external ADC.
+12V
+
RSENSE1
LOAD1
OUT
±
LOAD1
INA2180 Dual Current
Sense Amplifier
OP-AMP1
INA180
IN+
DC/DC
Power
Supply
IN±
Memory
OUT1
RSENSE1
+
OUT1
±
2:1
MUX
INA180
IN+
DC/DC
LOAD2
ADC
LOAD2
Control
OP-AMP2
+
RSENSE1
OUT
±
+
OUT2
RSENSE2
±
RSENSE2
Other
Loads
Figure 1. Discrete vs. Integrated Current Sensing
Solutions
In this case, the operational amplifier-based solution
requires 8 resistors to set the gain, 2 bypass
capacitors and 2 current sense resistors. The same
circuit implemented with an INA2180 only requires the
2 current sense resistors and a single bypass
capacitor. Since the integrated gain-set resistors are
well matched, the accuracy of the INA2180 solution is
much better than what can be achieved in a cost
effective discrete implementation. The integrated gainset resistors permit higher accuracy monitoring or
SLYA024 – December 2017
Submit Documentation Feedback
IN±
OUT2
PProcessor
Figure 2. Monitoring Total Current in Two Supply
Rails
One approach would be to monitor both the CPU and
memory current, multiplex the current to an ADC and
then and add the resulting values together in a
microprocessor. This approach requires some
mathematical processing as well as an ADC to
continually sample outputs at a fast enough rate to be
effective. A better approach would be to use the REF
pin of the INA2181 to add the current drawn by the
memory to the current drawn by the CPU. This can be
done by connecting the output of channel 1 that
monitors the memory current to the REF2 pin as
shown in Figure 3.
Common Uses for Multi-channel Current Monitoring Dennis Hudgins, Current Sensing
Copyright © 2017, Texas Instruments Incorporated
Products
1
www.ti.com
+12V
Power
Supply
INA2181
REF1
IN+1
INA2181
IN+1
DC/DC
+
RSENSE
+
RSENSE
OUT1
IN±1
IN±1
LOAD
REF2
IN+2
IN+2
DC/DC
REF2
+
RSENSE
+
RSENSE
OUT1
±
±
Memory
VREF1
REF1
OUT2
OUT2
ADC
±
ADC
±
IN±2
Other
Loads
GND
IN±2
PProcessor
VOUT2 = VREF1 if there is no leakage current
GND
VOUT2 = (ILOAD1 + ILOAD2) × RSENSE × GAIN
Figure 4. Current Subtraction using the INA2181,
for Leakage Current Detection
Figure 3. Analog Current Summing with INA2181
The channel 2 output will be the amplified sum of the
currents from the CPU and memory. The current from
the memory and the current from the total can be
monitored when desired by an ADC. However, since
the channel 2 output is an analog signal, a comparator
with an appropriately set reference can be used to
interrupt the system when an over current condition
occurs. For this circuit to function properly the values
of the two sense resistors must be the same.
Another convenient use for multi-channel current
monitors is to detect unexpected leakage paths. These
leakage paths could be caused by unintended shorts
to ground or some other potential not in the current
measurement path. One technique to detect leakage
current paths is to monitor all current going into and
coming out of a circuit. As long as there are no
unexpected leakage paths, the current into the load
must equal the current coming out. To detect leakage
currents all current in and out of a circuit should be
monitored. If the currents in and out are equal, no
unexpected current leakage path will be detected. Use
of the dual current monitor provides a simple
technique to detect leakage current paths without the
need for multiple devices or the need to externally add
or subtract currents. The circuit shown in Figure 4,
uses the INA2181 to monitor the current into and out
of a load.
By reversing the polarity of the resistor connections of
the second amplifier and connecting the output of the
first amplifier to the second amplifier, the current going
in to the load is subtracted from the current going out.
2
If the voltage at OUT2 is equal to the applied
reference voltage then no leakage path exists. If VOUT2
is higher than the applied reference voltage then there
is unexpected current leaving the load. Likewise if
VOUT2 is below the reference voltage then unexpected
leakage current is entering the load. As before, for this
circuit to function properly the values of the current
sense resistors must be the same.
Texas Instruments offers several solutions for
multichannel current monitoring. To monitor 4
channels the INA4180 and INA4181 devices are
available with and analog voltage output. The INA3221
provides the ability to accurately measure both system
current and bus voltages for up to 3 independent
channels. The values of the currents and voltages are
reported through an I2C compatible interface.
Table 1. Alternative Device Recommendations
Device
Optimized Parameters
Performance Trade-Off
INA4180
4 channel analog current
monitor
Unidirectional
Measurement, larger
package
INA4181
Bidirectional 4 channel
current monitor
Larger package
INA3221
3 channel digital
current/voltage monitor
No analog output
Table 2. Adjacent Tech Notes
SBOA162
SBOA169
Precision, Low-Side Current Measurement
SBOA190
Low-Side Current Sense Circuit Integration
Common Uses for Multi-channel Current Monitoring Dennis Hudgins, Current Sensing
Products
Measuring Current To Detect Out-of-Range
Conditions
Copyright © 2017, Texas Instruments Incorporated
SLYA024 – December 2017
Submit Documentation Feedback
IMPORTANT NOTICE FOR TI DESIGN INFORMATION AND RESOURCES
Texas Instruments Incorporated (‘TI”) technical, application or other design advice, services or information, including, but not limited to,
reference designs and materials relating to evaluation modules, (collectively, “TI Resources”) are intended to assist designers who are
developing applications that incorporate TI products; by downloading, accessing or using any particular TI Resource in any way, you
(individually or, if you are acting on behalf of a company, your company) agree to use it solely for this purpose and subject to the terms of
this Notice.
TI’s provision of TI Resources does not expand or otherwise alter TI’s applicable published warranties or warranty disclaimers for TI
products, and no additional obligations or liabilities arise from TI providing such TI Resources. TI reserves the right to make corrections,
enhancements, improvements and other changes to its TI Resources.
You understand and agree that you remain responsible for using your independent analysis, evaluation and judgment in designing your
applications and that you have full and exclusive responsibility to assure the safety of your applications and compliance of your applications
(and of all TI products used in or for your applications) with all applicable regulations, laws and other applicable requirements. You
represent that, with respect to your applications, you have all the necessary expertise to create and implement safeguards that (1)
anticipate dangerous consequences of failures, (2) monitor failures and their consequences, and (3) lessen the likelihood of failures that
might cause harm and take appropriate actions. You agree that prior to using or distributing any applications that include TI products, you
will thoroughly test such applications and the functionality of such TI products as used in such applications. TI has not conducted any
testing other than that specifically described in the published documentation for a particular TI Resource.
You are authorized to use, copy and modify any individual TI Resource only in connection with the development of applications that include
the TI product(s) identified in such TI Resource. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE TO
ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY TECHNOLOGY OR INTELLECTUAL PROPERTY
RIGHT OF TI OR ANY THIRD PARTY IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
regarding or referencing third-party products or services does not constitute a license to use such products or services, or a warranty or
endorsement thereof. Use of TI Resources may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
TI RESOURCES ARE PROVIDED “AS IS” AND WITH ALL FAULTS. TI DISCLAIMS ALL OTHER WARRANTIES OR
REPRESENTATIONS, EXPRESS OR IMPLIED, REGARDING TI RESOURCES OR USE THEREOF, INCLUDING BUT NOT LIMITED TO
ACCURACY OR COMPLETENESS, TITLE, ANY EPIDEMIC FAILURE WARRANTY AND ANY IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF ANY THIRD PARTY INTELLECTUAL
PROPERTY RIGHTS.
TI SHALL NOT BE LIABLE FOR AND SHALL NOT DEFEND OR INDEMNIFY YOU AGAINST ANY CLAIM, INCLUDING BUT NOT
LIMITED TO ANY INFRINGEMENT CLAIM THAT RELATES TO OR IS BASED ON ANY COMBINATION OF PRODUCTS EVEN IF
DESCRIBED IN TI RESOURCES OR OTHERWISE. IN NO EVENT SHALL TI BE LIABLE FOR ANY ACTUAL, DIRECT, SPECIAL,
COLLATERAL, INDIRECT, PUNITIVE, INCIDENTAL, CONSEQUENTIAL OR EXEMPLARY DAMAGES IN CONNECTION WITH OR
ARISING OUT OF TI RESOURCES OR USE THEREOF, AND REGARDLESS OF WHETHER TI HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
You agree to fully indemnify TI and its representatives against any damages, costs, losses, and/or liabilities arising out of your noncompliance with the terms and provisions of this Notice.
This Notice applies to TI Resources. Additional terms apply to the use and purchase of certain types of materials, TI products and services.
These include; without limitation, TI’s standard terms for semiconductor products http://www.ti.com/sc/docs/stdterms.htm), evaluation
modules, and samples (http://www.ti.com/sc/docs/sampterms.htm).
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2017, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertising