Key Specs

SpecValueConditionSource
Amplifier TypeCurrent SenseDigi-Key
Current Input Bias20 µADigi-Key
Gain Bandwidth Product1 MHzDigi-Key
Mounting TypeSurface MountDigi-Key
Number Of Circuits1Digi-Key
Operating Temperature Range-40°C ~ 125°C (TA)Digi-Key
Output Type-Digi-Key
Package CaseSC-74A, SOT-753Digi-Key
Quiescent Current (Typ)1.5mADigi-Key
Slew Rate2.5V/µsDigi-Key
Supplier Device PackageSOT-23-5Digi-Key
Voltage Input Offset30 µVDigi-Key
Voltage Supply Span (Max)20 VDigi-Key
Voltage Supply Span (Min)2.7 VDigi-Key

When To Use

  1. Precision high-side current sensing on 12V bus → 0.1–10A with 5mΩ shunt: The 30 µV input offset limits measurement error at 1A (5mV shunt drop) to 0.6% — the the B2 gain variant (same package, 1.3 MHz GBW, 55µV offset)‘s 55µV offset doubles this to 1.1%. For a power meter calibrated once at production without digital auto-zero, that 45µV offset difference is the noise floor. Choose B3 over B2 specifically when offset accuracy is the binding constraint and the 1.3 MHz vs 1 MHz GBW difference is acceptable. A Hall-effect sensor avoids shunt loss but cannot match 30µV-class offset without expensive signal conditioning.

  2. Industrial 24V power distribution current monitoring → 0–20A, -40°C to 125°C: The 20V maximum supply covers 24V nominal rails when pre-regulated to 20V through the sense circuit, while the wide temperature range suits industrial DIN-rail environments. The 1.5mA quiescent current is appropriate for continuously active 24V power management circuits — use the an ultra-low-IQ CSA (sub-2µA quiescent class) class if sub-100µA IQ is required on the 24V rail.

  3. Active power supply current monitoring where 30µV offset outweighs GBW (dc–10kHz signal content): Within the INA281B series, choose B3 when offset error is tighter than B2’s 55µV limit and the 1MHz GBW is sufficient for the application bandwidth. When the bandwidth requirement exceeds 1MHz or offset is acceptable at 55µV, select the B2 gain variant (same package, 1.3 MHz GBW, 55µV offset) — identical package and supply range, lower cost, higher GBW.

When Not To Use

  1. Measuring fast transient currents with high di/dt in switching power supplies: The 1 MHz gain-bandwidth product limits response speed and may cause output distortion or ringing. Use a higher-bandwidth current-sense amplifier to capture transient waveforms without aliasing or signal integrity loss.

  2. Detecting sub-µA leakage currents in precision instrumentation: The 30 µV input offset voltage and 20 µA input bias current exceed the noise floor for ultra-low current sensing. A lower-offset current-sense amplifier is required to avoid offset-induced measurement errors and ensure accurate leakage detection.

  3. High-side current sensing in isolated AC mains applications: This device lacks galvanic isolation, which is critical to prevent ground loops and ensure user safety. Employ an isolated current-sense amplifier to maintain isolation barrier and avoid catastrophic damage or personal injury.

Application Notes

Gotchas

  1. [Ignoring input bias current effect on shunt resistor]: Engineers may assume the 20 µA input bias current is negligible at all shunt resistor values. In reality, large shunt resistors cause offset voltage drops that shift measured current, leading to inaccurate readings or false alarms. Fix by choosing shunt resistor values that balance sensitivity and input bias error, and verify offset voltage with actual load current applied.

  2. [No thermal relief on PCB for SOT-23-5]: The small package and limited thermal conduction can cause local hotspots if copper pours are not properly connected or thermal vias omitted. This leads to drift in offset voltage and eventual device stress. Fix by designing dedicated thermal pads and using at least two thermal vias under or near the package.

  3. [Routing input traces near noisy switching nodes]: Placing the current-sense input lines close to fast switching nodes (SW) induces high-frequency noise, corrupting the low-level sense signal and causing output jitter or false triggering in downstream logic. Fix by routing input traces away from SW nodes and adding guard traces tied to ground around sensitive inputs.

  4. [Failure to account for minimum supply voltage during startup]: The device requires at least 2.7 V supply voltage; powering from slowly rising rails or battery stacks without sequencing may cause the output to remain undefined or saturate during startup, confusing system diagnostics. Fix by verifying supply ramp timing and adding power-good signals or reset logic to downstream circuitry.