Texas Instruments | High-side, bidirectional current-sensing circuit with transient protection (Rev. A) | Application notes | Texas Instruments High-side, bidirectional current-sensing circuit with transient protection (Rev. A) Application notes

Texas Instruments High-side, bidirectional current-sensing circuit with transient protection (Rev. A) Application notes
Analog Engineer's Circuit: Amplifiers
SBOA299A – May 2018 – Revised February 2019
High-side, bidirectional current-sensing circuit with
transient protection
Design Goals
Input
Output
Supply
Standoff and Clamp
Voltages
EFT Level
IinMin
IinMax
VoMin
VoMax
Vs
GND
Vref
Vwm
Vc
Vpp
–40A
40A
100mV
4.9V
5V
0V
2.5V
36V
80V
2kV 8/20µs
Design Description
This high-side, bidirectional current sensing solution can accurately measure current in the range of –40A
to 40A for a 36-V voltage bus. The linear voltage output is 100mV to 4.90V. This solution is also designed
to survive IEC61000-4-4 level 4 EFT stress (Voc = 2kV; Isc = 40A; 8/20µs).
Design Notes
1. This solution is targeted toward high-side current sensing.
2. The sense resistor value is determined by minimum and maximum load currents, power dissipation
and Current Shunt Amplifier (CSA) gain.
3. Bidirectional current sensing requires an output reference voltage (Vref). Device gain is achieved
through internal precision matched resitor network.
4. The expected maximum and minimum output voltage must be within the device linear range.
5. The TVS diode must be selected based on bus voltage, the CSA common-mode voltage specification,
and EFT pulse characteristics.
SBOA299A – May 2018 – Revised February 2019
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Design Steps
1. Determine the maximum output swing:
2. Determine the maximum value of the sense resistor based on maximum load current, swing and
device gain. In this example, a gain of 20 was chosen to illustrate the calculation, alternative gain
versions may be selected as well:
3. Calculate the peak power rating of the sense resistor:
4. Determine TVS standoff voltage and clamp voltage:
5. Select a TVS diode.
For example, SMBJ36A from Littelfuse™ satisfies the previous requirement, with peak pulse power
of 600W (10/1000µs) and current of 10.4A.
6. Make sure the TVS diode satisfies the design requirement based on the TVS operating curve.
Peak pulse power at given excitation (8/20µs) is estimated to be around 3.5kW, which translates to
peak pulse current:
This is above the maximum excitation (short circuit) current of 40A. The select TVS effectively protects the
circuit against the specified EFT strike.
2
High-side, bidirectional current-sensing circuit with transient protection
SBOA299A – May 2018 – Revised February 2019
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Design Simulations
DC Transfer Characteristics
Transient Simulation Results
The output is a scaled version of the input.
SBOA299A – May 2018 – Revised February 2019
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TVS Diode Transient Response Under EFT Excitation
4
High-side, bidirectional current-sensing circuit with transient protection
SBOA299A – May 2018 – Revised February 2019
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Copyright © 2018–2019, Texas Instruments Incorporated
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Design References
See Analog Engineer's Circuit Cookbooks for TI's comprehensive circuit library.
For more information on transient protection of the current sense amplifiers, see TIDA-00302 and the
Current Sense Amplifier Training Videos.
Design Featured Current Sense Amplifier
INA240A1
Vs
2.7V to 5.5V
VCM
–4V to 80V
Vos
Rail-to-rail
Vos
5µV
IB
80µA
BW
400kHz
Vos Drift
50nV/°C
http://www.ti.com/product/INA240
Design Alternate
INA282
Vs
2.7V to 18V
VCM
–14V to 80V
Vos
20µV
IB
25µA
BW
10kHz
Vos Drift
0.3µV/°C
http://www.ti.com/product/INA193
Revision History
Revision
Date
A
February 2019
Change
Changed VinMin and VinMax in the Design Goals table to IinMin and IinMax, respectively.
SBOA299A – May 2018 – Revised February 2019
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High-side, bidirectional current-sensing circuit with transient protection
Copyright © 2018–2019, Texas Instruments Incorporated
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