Allegro MicroSystems A4931MET-T

Overview

A4931MET-T from Allegro MicroSystems is a 3-phase brushless DC motor pre-driver IC designed to control six external N-channel MOSFETs in full-bridge configurations. It supports motor supply voltages up to 30 V, uses three 120°-spaced Hall inputs for commutation, and integrates fixed off-time PWM current control (25 μs typ), synchronous rectification, locked-rotor protection, thermal shutdown (170°C trip), and overvoltage protection (33 V threshold). It is used in compact BLDC motor control systems such as power tools and HVAC blowers.

For engineers reviewing the A4931MET-T datasheet, A4931MET-T pinout, A4931MET-T application, or A4931MET-T equivalent, key selection criteria include Hall-based commutation support, 28-pin QFN package with exposed thermal pad, FG1/FG2 speed feedback outputs, synchronous rectification capability, and compatibility with external N-channel MOSFET half-bridges.

Technical Context

The A4931MET-T implements Hall-sensor-driven six-step commutation logic with internal state decoding across HA±, HB±, HC± inputs. Its gate drive architecture delivers 30 mA sourcing current per output, 28 Ω pull-down resistance, and 1 μs dead time (700–1300 ns) to prevent shoot-through during high/low-side switching transitions.

Current regulation uses a fixed off-time PWM scheme triggered at 200 mV sense threshold (ITRIP = 200 mV / RSENSE), with blanking timer (1.5 μs) to reject switching transients. Synchronous rectification is dynamically disabled during overvoltage events (VBBOV > 33 V) to prevent uncontrolled regenerative energy feedback into the supply rail.

Key Specifications

Pinout & Package

The A4931MET-T is housed in a 5 mm × 5 mm, 0.90 mm nominal height, 28-terminal QFN package (ET package) with exposed thermal pad for enhanced thermal dissipation (RθJP = 2°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-phase BLDC pre-driver applications.

Compared with A4931MET-T, MP6532GQ-Z lacks integrated Hall biasing and lock-detect timing, while STSPIN32F0A replaces fixed six-step commutation with programmable FOC - making A4931MET-T optimal for cost-sensitive, Hall-sensor-based BLDC systems needing minimal external components and proven reliability.

Availability

A4931MET-T is available at Aetrix Electronics and suitable for power tools, HVAC blowers, automotive cooling fans, and industrial pumps requiring stable component supply and long-term production continuity.

Supply support for A4931MET-T includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Allegro MicroSystems is a U.S.-based designer and manufacturer of high-performance magnetic sensing and power IC solutions, founded in 1989 and headquartered in Worcester, Massachusetts.

The A4931MET-T belongs to Allegro's motor driver product line, engineered specifically for cost-effective, Hall-sensor-commutated BLDC motor control in consumer, industrial, and automotive applications where reliability, thermal robustness, and minimal external component count are critical.

FAQ

What is the function of the CLD pin on the A4931MET-T?

The CLD pin on the A4931MET-T sets the locked-rotor detection timeout using an external capacitor. With a 0.1 μF capacitor, the A4931MET-T waits 2 seconds before disabling outputs if Hall transitions stall or repeat. The A4931MET-T uses this signal to generate a triangle waveform; 127 cycles define tlock, enabling configurable fault response without firmware. Connecting CLD to GND disables lock detection entirely.

How does synchronous rectification work in the A4931MET-T, and when is it disabled?

Synchronous rectification in the A4931MET-T turns on appropriate low-side MOSFETs during current decay to bypass body diodes, reducing conduction loss. It is automatically disabled when VBB exceeds the overvoltage threshold (33 V typical), preventing regenerative energy from pumping the supply rail. This behavior is hardware-controlled and requires no external intervention - the A4931MET-T handles it autonomously during motor deceleration or downhill regeneration.

What is the purpose of the HBIAS pin on the A4931MET-T, and what load can it drive?

The HBIAS pin on the A4931MET-T provides a regulated 7.5 V ±0.3 V supply to power external Hall-effect sensors and internal logic. It is current-limited to 30 mA maximum, sufficient to drive three typical bipolar Hall latches (e.g., A342x series) simultaneously. The A4931MET-T integrates this function to eliminate the need for an external LDO, simplifying system design and reducing BOM count.

Can the A4931MET-T operate without external Hall sensors?

No, the A4931MET-T requires three differential Hall sensor inputs (HA±, HB±, HC±) for six-step commutation and cannot operate in sensorless mode. Its internal logic decodes Hall state transitions to determine phase sequencing; absence of valid Hall signals results in stalled or undefined motor behavior. The A4931MET-T does not include back-EMF sensing circuitry or algorithms - Hall sensors are mandatory for correct operation.

What thermal performance can be expected from the A4931MET-T in a standard 4-layer PCB layout?

In a JEDEC-standard 4-layer PCB layout, the A4931MET-T achieves a junction-to-ambient thermal resistance (RθJA) of 32°C/W and a junction-to-pad resistance (RθJP) of 2°C/W. With proper thermal vias under the exposed pad, the A4931MET-T sustains continuous 1.5 A RMS gate drive current at 105°C ambient. Its 150°C max junction temperature and 15°C thermal hysteresis ensure stable operation under transient overload conditions.