Allegro MicroSystems A3936SED-T

Overview

A3936SED-T from Allegro MicroSystems is a three-phase brushless DC motor driver IC with ±3 A peak output current, 50 V operating voltage, and integrated PWM current control with configurable slow/fast/mixed decay modes. It features synchronous rectification, thermal shutdown with hysteresis, crossover-current protection, and tachometer output - used in closed-loop speed-controlled BLDC motor systems for industrial automation and precision motion control.

For engineers reviewing the A3936SED-T datasheet, A3936SED-T pinout, A3936SED-T application, or A3936SED-T equivalent, key selection criteria include its 44-pin PLCC package with fused ground leads, fixed off-time PWM timing (typically 24 µs), Hall sensor interface compatibility, and absence of required power-up sequencing.

Technical Context

The A3936SED-T implements a DMOS-based three-phase H-bridge with independent source/sink drivers, each rated for ±3 A peak current and featuring low R_DS(on) (0.55 Ω source / 0.35 Ω sink). Its internal oscillator (3.4–4.6 MHz, set by external 51 kΩ resistor) drives a fixed off-time PWM controller that regulates motor winding current via VREF and sense resistor feedback.

Commutation logic accepts six Hall sensor inputs (HA±, HB±, HC±) to determine rotor position and drive sequence; decay mode is selected via PFD1/PFD2 pins (0–100% fast decay), while SR pin enables synchronous rectification to replace body-diode conduction during current recirculation - reducing power dissipation and eliminating need for external Schottky diodes.

Key Specifications

Pinout & Package

The A3936SED-T is housed in a 44-pin plastic leaded chip carrier (PLCC) with internally fused ground leads (three per side) connected to the exposed power ground tab (Pin 44). These fused leads are at GND potential and require no electrical isolation, enhancing thermal performance in high-current applications.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STSPIN32F0A and DRV8313, the A3936SED-T delivers turnkey Hall-based commutation and analog tach feedback in a single IC - reducing BOM count and firmware complexity for cost-sensitive, sensor-based BLDC systems where FOC is not required.

Availability

A3936SED-T is available at Aetrix Electronics and suitable for industrial conveyor systems, medical infusion pumps, automated guided vehicles (AGVs), and lab automation robotics requiring stable component supply, Pb-free compliance, and long-term production continuity.

Supply support for A3936SED-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 global leader in magnetic sensing and power IC design, specializing in high-reliability semiconductor solutions for motion control, power management, and sensing applications.

The A3936 product line was engineered specifically for cost-effective, Hall-sensor-based three-phase BLDC motor control in industrial and medical equipment - emphasizing integrated protection, thermal robustness, and simplified system-level design.

FAQ

What is the maximum continuous motor supply voltage supported by the A3936SED-T?

The A3936SED-T supports a continuous motor supply voltage (VBB) of up to 50 V, with absolute maximum rating also at 50 V. Operation at this voltage requires adherence to thermal limits - junction temperature must not exceed +150 °C under any duty cycle or ambient condition. Derating is necessary above +85 °C ambient, and proper heatsinking via the fused ground leads is essential at full 50 V/±3 A operation.

Does the A3936SED-T require external MOSFETs, or are they integrated?

The A3936SED-T integrates DMOS power MOSFETs for all six phases of the three-phase H-bridge - no external MOSFETs are required. Each output stage includes matched source and sink drivers with specified R_DS(on) (0.55 Ω source, 0.35 Ω sink) and built-in protection against cross-conduction, thermal overload, and undervoltage conditions.

How does the tachometer output on the A3936SED-T function, and what load can it drive?

The TACH pin (Pin 27) is an open-collector output that toggles low on every Hall sensor transition - providing a pulse-per-commutation event. It can sink ≥500 µA at ≤0.5 V saturation, allowing direct interface with 3.3 V or 5 V microcontroller inputs using a pull-up resistor (typically 4.7–10 kΩ). No external buffering is needed for standard logic-level speed feedback.

Can the A3936SED-T operate without external Hall sensors?

No - the A3936SED-T requires six differential Hall sensor inputs (HA±, HB±, HC±) for commutation and cannot operate in sensorless mode. Its internal logic is hardwired for 120° Hall-based sequencing; there is no provision for back-EMF sensing, encoder interfacing, or microcontroller-driven trapezoidal control without Hall inputs.

What is the purpose of the fused ground leads in the A3936SED-T PLCC package?

The fused ground leads (Pins 1,2,11,12,13,22,23,24,33,34,35,44 plus the exposed tab at Pin 44) provide low-thermal-resistance paths from the die to the PCB ground plane. They are electrically tied to GND and require no isolation - enabling efficient heat transfer during ±3 A peak operation, especially critical in compact industrial motor drive modules.