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A current-sense amplifier can appear to have a gain error when the real problem is that the differential voltage reaching its input pins is not the same as the voltage across the shunt element. Use a Kelvin connection to sense the shunt itself, route the two sense traces short and balanced, and measure voltage directly at the amplifier pins when diagnosing a discrepancy.
Why the amplifier may not see the shunt voltage
In an ideal circuit, the voltage across the shunt, Vshunt, is the voltage measured by the monitor. On a real PCB, copper traces and vias have resistance. The differential voltage at the device inputs, Vsense, can therefore differ from Vshunt.
Resistance in the high-current path that is in series with the shunt can add to or subtract from the voltage presented to the sense inputs. The result is a layout-related measurement error that may be mistaken for an amplifier gain problem. Input-trace resistance can introduce another error: the device’s input bias currents flowing through those traces create voltage drops, and unequal trace resistance can turn the drops into a differential offset.
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Route each amplifier input to a separate sense point at the shunt element’s terminals. Those connections should carry the small input currents, not share a length of copper carrying the load current. This four-wire arrangement lets the amplifier sense the voltage across the resistive element rather than the voltage drop in intervening high-current copper. Texas Instruments’ INA28x Rev. C datasheet explicitly advises: connect the input pins to the sensing resistor using a Kelvin or 4-wire connection.
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Keep the sense routes short and balanced, and place the shunt and monitor on the same PCB side when practical so the input routes can avoid vias. Vias and trace geometry contribute parasitic resistance; temperature variation can also change resistance. Same-side placement is a practical way to simplify the sense path, not a substitute for connecting at the shunt’s actual sense terminals.
Keep the two input paths balanced
Similar lengths and geometries help keep the two paths’ resistances alike, reducing differential voltage created by input bias currents. Do not intentionally make one trace longer or narrower to compensate for an assumed bias-current mismatch: the mismatch varies from device to device and with operating conditions, so a fixed layout imbalance is not a dependable correction.
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The 2012 EE Times tutorial by Texas Instruments applications engineers Pete Semig and Collin Wells illustrates why trace geometry matters. In their example, one-ounce copper with a 350 mil-long, 10 mil-wide input trace was estimated at approximately 17 mΩ. Their simulation comparison found a 35.7% increase in error when the two example input traces differed by 75 mil (275 mil versus 350 mil). These are results for the article’s particular example, not predictions for every board. The authors also estimated approximately 193 µΩ for an example one-ounce copper high-current trace 10 mil long and 25 mil wide—small resistance that can still matter in a precision measurement.
Measure at the device pins to find the source of error
When troubleshooting, measure the differential voltage between the amplifier’s input pins and use that voltage to evaluate the device’s gain. Comparing output only with the voltage measured across the shunt element combines any board-layout error with the device’s own gain error. The authors’ recommendation is to measure at the input pins rather than rely on the shunt voltage alone.
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The tutorial’s simulation example makes the distinction concrete. With an 80 mV shunt voltage and nominal gain of 50 V/V, the expected output is 4 V; the simulated output was 4.084 V, an apparent 2.1% discrepancy against that shunt-based calculation. When the authors used the actual sense voltage at the inputs, they calculated 0.3% device error. This is the authors’ simulation example, not a field measurement.
- Measure the shunt voltage at the shunt element’s sense terminals.
- Measure the differential voltage directly between the amplifier input pins under the same operating conditions.
- Compare those voltages. A difference points to the sense routing, high-current copper, or other parasitic resistance between the measurement points.
- Use the pin-to-pin differential voltage with the expected gain when calculating the amplifier’s gain error; then investigate other device or circuit errors if the discrepancy remains.
What the INA282 example does—and does not—establish
The 2012 tutorial’s design example assumes a 70 V common-mode voltage, 5 V supply, unidirectional sensing, a 5 A to 10 A load range, and a high-accuracy goal. It selects an INA282 with 50 V/V gain and an 8 mΩ shunt, subject to tolerable shunt power dissipation. For that example, the article gives an output swing of 40 mV to 4.6 V and derives an input range of 0.8 mV to 92 mV. These values belong to those assumptions; the 8 mΩ value is not a general shunt recommendation.
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As checked October 4, 2026, Texas Instruments’ INA282 product page lists the device as active and specifies 50 V/V gain and 10 kHz bandwidth. It also lists a −14 V to +80 V common-mode input range and a maximum input offset of 70 µV. These are device characteristics, not a general recommendation for this part; confirm lifecycle status, the current datasheet, and operating conditions before choosing it. The INA28x datasheet cited above is Rev. C from May 2015, so verify specifications against the latest documentation for the exact part.
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Selection checks before committing the layout
Current-sense monitor
- Common-mode and supply-voltage ranges for the intended operating conditions.
- Gain, input offset and drift, bandwidth, and output range.
- Unidirectional or bidirectional measurement needs, operating temperature, package, and current availability.
Shunt resistor
- Resistance and maximum current, including power dissipation, thermal limits, and derating.
- Tolerance, temperature coefficient, and pulse behavior.
- Terminal geometry that supports a true Kelvin connection.
The INA282-286EVM is TI’s evaluation module for functional device evaluation. TI says its fixture is not intended as a target circuit layout or an EMC test layout, so it should not be treated as a ready-made PCB-layout reference.
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