INA281 Current Sensor: 7 Checks for an Honest Error Budget

INA281 Current Sensor: 7 Checks for an Honest Error Budget

Build an INA281 error budget with seven checks for gain variants, offset limits, shunt heating, common-mode feedthrough and low-current validity. This is a documentation-based planning guide, not a report of independent hands-on testing.

1. Start with the full order code and a bounded experiment

INA281 provides fixed gains of 20, 50, 100, 200 and 500 V/V, selected by the numbered variant. The A and B options also have different sense and supply pin positions. Verify the complete package drawing before connecting a board. This guide focuses on estimating measurement uncertainty, not merely producing an output. Begin with an isolated, current-limited low-voltage supply and a benign load; the high common-mode rating does not provide isolation or make exposed hazardous-voltage experiments appropriate. Manufacturer documentation.

2. Keep supply, common-mode and differential limits separate

The amplifier supply range is 2.7 V to 20 V, while the specified input common-mode operating range is -4 V to 110 V. Survival ratings are not normal measurement limits. Output span and gain impose another limit on useful shunt voltage. The device is unidirectional, so negative common-mode capability does not create a signed reverse-current output. Write these separate envelopes into the test plan, including ADC input limits and protection when the amplifier supply exceeds the host rail. Manufacturer documentation.

3. Convert offset voltage into current uncertainty

For a chosen shunt, input-referred offset contributes approximately offset voltage divided by shunt resistance to current error. For the gain-50 variant, the table gives a typical 55-microvolt offset and a maximum 300-microvolt offset under its stated conditions. With 10 milliohms, those correspond to 5.5 mA typical and 30 mA maximum before other errors. These are not interchangeable accuracy claims. Check the exact variant and temperature conditions instead of promoting the smallest headline typical value into a system guarantee. Manufacturer documentation.

4. Add gain and shunt errors without double-counting

The ideal output follows fixed gain multiplied by shunt resistance and current. Gain error is specified separately from input offset, and shunt resistance has its own tolerance and temperature coefficient. At larger current, percentage terms can dominate; near zero, offset and output floor are usually more important. Calculate shunt dissipation as current squared multiplied by resistance, then estimate temperature rise using the actual mounting. A room-temperature resistor tolerance does not describe its resistance after sustained load heating. Manufacturer documentation.

5. Distinguish DC rejection from switching-edge behavior

The electrical table specifies common-mode rejection under DC conditions and gives a separate typical AC figure at 50 kHz. These describe different tests. A high DC rejection number cannot prove that a switching supply edge produces no output disturbance. Source impedance mismatch, trace inductance and measurement probe grounding can add errors. Observe common-mode steps separately from intended current steps using a safe fixture, and document any sampling blanking or filtering needed before interpreting the output as a settled current measurement. Manufacturer documentation.

6. Build a lower-current validity boundary

Increasing gain makes an ADC see a larger output change but does not remove input offset or create bidirectional headroom. The output also approaches a finite floor near ground. Define a lower reporting limit from the complete error budget and measured noise, rather than from ADC bit depth alone. If uncertainty spans a large fraction of the requested current, return a qualified low-current indication. Averaging can reduce some random noise, but it does not eliminate fixed offset, gain error or shunt self-heating. Manufacturer documentation.

7. Validate the budget against reference measurements

Record supply, exact suffix, shunt resistance, temperature and ADC settings with each run. Compare several stable positive currents, including the intended minimum and maximum, against a suitable reference instrument. Repeat after warm-up and investigate deviations before fitting a correction. Keep calibration data distinct from manufacturer limits, and document residual uncertainty after correction. A useful final record includes raw output, converted current, sample age and validity status; it should not imply that documentation-based calculations alone constitute independent calibration. Manufacturer documentation.

Related reading: INA293 Current Amplifier: 7 Checks for Pinouts and Zero-Current Limits.

Catalog note: The exact-part search did not return a matching Epro listing during preparation. Check the current catalog; this guide makes no price, availability or included-accessory claim.