SBOA529 October 2021 INA293 , INA293

**Design Goals**

The design goal is the realization of a bidirectional current sensing circuit with a unidirectional current sense amplifier.

Input | Output | Supply |
Error |
|||
---|---|---|---|---|---|---|

I_{Min} |
I_{Max} |
V_{out, min} |
V_{out, max} |
V_{cc} |
V_{ee} |
Over input current range |

–10 A | +10 A | About 100 mV | About 4 V | 5 V | 0 V | ≤ 3% at room temperature ≤ 5% from 0°C to 85°C |

**Design Description**

This design utilizes a unidirectional current shunt monitor to measure a bidirectional load current. This concept only works for low-side current sensing applications. The load current range is from –10 A to +10 A, the output range is from 100 mV to 4 V, and the supply voltages are 5 V and ground.

**Design Notes**

- Analyze unidirectional current measurement circuit
- Change the circuit to measure
bidirectional current.

Use 0.1% tolerance resistors for R1 and R2 with a temperature coefficient of 10 ppm. An example, is the TNPW0603e3 resistor from Vishay® - Error calculation over input current and temperature
- As an example, the INA293A1 amplifier is used in this design note, but the concept is valid for many different current shunt monitors with input-bias-current information available and capable of low-side measurement
- Be sure to Kelvin-connect the shunt resistor
- Conduct a 1-point offset calibration at 25°C to compensate for resistor tolerances

**Design
Steps**

- Unidirectional current
measurement standard circuit:

Reversing the current in the previous example results in a negative voltage at the IN+ pin of the INA293A1 which will not disturb the part but results in an output voltage close to 0 V.

- Biasing the input voltage of the
INA293A1 by 100 mV makes it possible to measure a bidirectional current from –10
A to 10 A with an input voltage from about 0 to 200 mV and an output voltage
from close to 0 V to 4 V:

Choosing R1 with 2 kΩ results in an error current of I

_{error}= (5 V – 0.201 V) / 2 kΩ = 2.4 mA which can be compensated after digitization in µC SW. To calculate R2, the input bias current of the INA293A1 must be considered. The input bias current into IN+ is taken from the data sheet: At 200 mV the current is typically about 60 µA (see the red dotted lines in*INA239x1 Input Bias Current vs V*), but could vary by ±20%. The simulation in the previous circuit shows the typical value. Because the IN– pin is connected to ground, this current can be ignored._{SENSE}

R2 = 100 mV / (2.4 mA – 60 µA) = 42.7 Ω. The closest E96 value is 43.2 Ω which results in a slightly higher input voltage of 201.1 mV as the

*Error Calculations R1 MAX R2 MIN*simulation shows. Choosing the higher value for R2 will also prevent the input going negative in case a current of –10 A is applied. - R1 and R2 are the only additional
error contributors compared to a unidirectional measurement. To get the
worst-case values for the input voltage of the current shunt monitor in the
*Error Calculations R1 MAX R2 MIN*schematics, a DC sweep from –10 A to +10 A is performed using*PSPICE-FOR-TI*.

**Design Results**

To calculate the worst-case error over temperature, check these two scenarios:

- R1max in combination with
R2min

*Error Calculations*:

All cases are simulated:

Measurements (mV) ^{(1)}^{(2)}^{(3)}^{(4)}^{(5)}^{(6)}Max(V(U1:IN+)) 201.16 201.36 **201.11**201.31 200.99 201.19 Min(V(U1:IN+)) 7.01 7.22 **6.96**7.17 6.84 7.04 (1) Nominal Values at 0°C(2) Worst-Case Values at 0°C(3) Nominal Values at 27°C(4) Worst-Case Values at 27°C(5) Nominal Values at 85°C(6) Worst-Case Values at 85°C - R1min in
combination with R2max

The input-voltage vs. input-current plot looks almost the same as under

.*R1max in combination with R2min*Measurements (mV) ^{(1)}^{(2)}^{(3)}^{(4)}^{(5)}^{(6)}Max(V(U1:IN+)) 201.06 201.25 **201.11**201.31 201.23 201.42 Min(V(U1:IN+)) 6.90 7.11 **6.96**7.17 7.08 7.29 (1) Nominal Values at 0°C(2) Worst-Case Values at 0°C(3) Nominal Values at 27°C(4) Worst-Case Values at 27°C(5) Nominal Values at 85°C(6) Worst-Case Values at 85°C

*Error at
27°C Room Temperature*

Because the difference between the worst-case (column 4) and nominal (column 3) curve is constant, this results in an error caused by R1 and R2 at 27°C of

201.31 mV / 201.11 mV – 1 = 0.1% at +10 A
and

7.17 mV
/ 6.96 mV – 1 = 3% at –10 A.

*Error Over Temperature
Range*

From the measurement tables, the minimum and maximum input voltages at IN+ are:

- –10 A: 6.84 mV and 7.29 mV, highlighted in green in the measurement tables
- +10 A: 200.99 mV and 201.42 mV, highlighted in blue in the measurement tables

Input Current | Error at Room Temperature 27°C | Error from 0°C to 85°C |
---|---|---|

–10 A | +3% | +4.47% | –1.72% |

+10 A | +0.1% | +0.15% | –0.06% |

Because the delta of the worst-case
voltages at V_{IN} stays constant over the whole current range, the error
becomes smaller with higher input voltage.

V_{OUT} can be calculated with
V_{IN} multiplied by 20, the gain of the INA293A1:

V_{out,min} = 6.84 mV × 20 = 137 mV and V_{out,max}
= 201.42 mV × 20 = 4.03 V which meets the design goal.

**Design
References**

See *Analog Engineer's Circuit Cookbooks* for TI's comprehensive
circuit library.

Download the PSpice files for this circuit – www.ti.com/lit/zip/SBOA529.

For more information on the INA293
device, see the *INA293 –4-V to 110-V, 1-MHz, High-Precision Current Sense
Amplifier* data sheet.

**Additional Resources**

- PSpice® for TI design and simulation tool:
*PSPICE-FOR-TI*