Three-Phase Current Sensing for BLDC Controllers: OEM Review Guide

Engineering note. This guide is published by the Sankey engineering content team for OEM planning. It explains the design decisions and evidence a project team should review; component datasheets, the intended end product, target-market requirements, and controlled laboratory testing remain the source of truth for a released design.

Current sensing supports torque control, current limiting, locked-rotor response, diagnostics, and power-stage protection. The measurement is only as useful as its location, timing, noise control, calibration, and behavior during switching transitions.

What this decision changes

The sensing architecture determines how accurately the controller sees phase current, how rapidly it can protect the power stage, which low-speed and high-duty-cycle conditions are observable, and what manufacturing calibration or offset checks are required.

Start with measurable inputs

Define peak and continuous current, required accuracy, current-limit response time, PWM method, ADC timing, bus voltage, allowed shunt loss, amplifier common-mode range, thermal environment, and whether phase-specific or bus-current information is needed.

Engineering review method

Choose shunt placement and amplifier topology with the real switching waveform in view. Establish sampling windows away from transition noise, define blanking only where justified, validate offset across temperature, and compare measured current against an independent reference at several operating points.

Evidence to keep with the design

Keep the current-path schematic, Kelvin-routing review, current-sense waveform captures, offset and gain records, ADC timing configuration, trip-response measurements, and calibration procedure. State the reference instrument and bandwidth used in comparisons.

Failure paths to challenge early

Typical problems include sampling during a noisy transition, losing a valid measurement at a duty-cycle extreme, routing sense and power current through the same impedance, allowing amplifier saturation to delay recovery, or setting a protection threshold without component and motor tolerance.

Before prototype release

Define the production checks for shunt value, offset, gain, current-limit trip, and fault recovery. Revisit the design after changes to PWM strategy, shunt supplier, amplifier, layout, or motor current profile.

Questions an OEM team should close

At which operating points is the current measurement least observable or least accurate?
What evidence shows the protection trip occurs before the power-stage limit is exceeded?
Which calibration values are stored, and how are they controlled in production?