Texas Instruments | High-side current-sensing circuit design (Rev. A) | Application notes | Texas Instruments High-side current-sensing circuit design (Rev. A) Application notes

Texas Instruments High-side current-sensing circuit design (Rev. A) Application notes
Analog Engineer's Circuit: Amplifiers
SBOA310A – December 2018 – Revised February 2019
High-side current-sensing circuit design
Design Goals
Input
Output
Supply
IiMin
IiMax
VoMin
VoMax
Vcc
Vee
50mA
1A
0.25V
5V
36V
0V
Design Description
This single–supply, high–side, low–cost current sensing solution detects load current between 50mA and
1A and converters it to an output voltage from 0.25V to 5V. High–side sensing allows for the system to
identify ground shorts and does not create a ground disturbance on the load.
R3 50.5k
Vcc
R2 1.01k
+
R1 100m
V
Vcc
+
Vi
U1 OPA192
+
Vo
R4 1.01k
Vbus 36
R5 50.5k
Iin
Design Notes
1. DC common mode rejection ratio (CMRR) performance is dependent on the matching of the gain
setting resistors, R2-R5.
2. Increasing the shunt resistor increases power dissipation.
3. Ensure that the common–mode voltage is within the linear input operating region of the amplifier. The
common mode voltage is set by the resistor divider formed by R2, R3, and the bus voltage. Depending
on the common–mode voltage determined by the resistor divider a rail–to–rail input (RRI) amplifier may
not be required for this application.
4. An op amp that does not have a common-mode voltage range that extends to Vcc may be used in
low–gain or an attenuating configuration.
5. A capacitor placed in parallel with the feedback resistor will limit bandwidth, improve stability, and help
reduce noise.
6. Use the op amp in a linear output operating region. Linear output swing is usually specified under the
AOL test conditions.
SBOA310A – December 2018 – Revised February 2019
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High-side current-sensing circuit design
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Design Steps
1. The full transfer function of the circuit is provided below.
2. Calculate the maximum shunt resistance. Set the maximum voltage across the shunt to 100mV.
3. Calculate the gain to set the maximum output swing range.
4. Calculate the gain setting resistors to set the gain calculated in step 3.
5. Calculate the common–mode voltage of the amplifier to ensure linear operation.
6. The upper cutoff frequency (fH) is set by the non–inverting gain (noise gain) of the circuit and the gain
bandwidth (GBW) of the op amp.
2
High-side current-sensing circuit design
SBOA310A – December 2018 – Revised February 2019
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Design Simulations
DC Simulation Results
5.00
Vo (V)
Iin=1A
Vo=5.003V
2.50
Iin=50mA
Vo=255.65mV
Iin=500mA
Vo=2.504V
0.00
250.00m
0.00
500.00m
Iin (A)
750.00m
1.00
AC Simulation Results
Gain (dB)
40.00
Vo / Iin
-3dBfrequency
frequency= =205.03kHz
205.03kHz
-3dB
20.00
0.00
Phase [deg]
0.00
-45.00
-90.00
1.0
10.0
SBOA310A – December 2018 – Revised February 2019
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100.0
1.0k
Frequency (Hz)
10.0k
100.0k
1.0M
High-side current-sensing circuit design
Copyright © 2018–2019, Texas Instruments Incorporated
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References:
1. Analog Engineer's Circuit Cookbooks
2. SPICE Simulation File SBOMAV4
3. TI Precision Labs
Design Featured Op Amp
OPA192
Vcc
4.5V to 36V
VinCM
Rail–to–rail
Vout
Rail–to–rail
Vos
5µV
Iq
1mA
Ib
5pA
UGBW
10MHz
SR
20V/µs
#Channels
1, 2, 4
www.ti.com/product/OPA192
Design Alternate Op Amp
OPA2990
Vcc
2.7V to 40V
VinCM
Rail–to–rail
Vout
Rail–to–rail
Vos
250µV
Iq
120µA
Ib
10pA
UGBW
1.25MHz
SR
5V/µs
#Channels
2
www.ti.com/product/OPA2990
Revision History
4
Revision
Date
A
February 2019
Change
Downstyle title.
Added Design Alternate Op Amp table.
High-side current-sensing circuit design
SBOA310A – December 2018 – Revised February 2019
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Copyright © 2018–2019, Texas Instruments Incorporated
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