Allegro MicroSystems A3938SLQTR

Overview

A3938SLQTR from Allegro MicroSystems is a three-phase brushless DC motor controller IC with integrated high-current N-channel MOSFET gate drivers, 50 V motor supply capability, internal 5 V logic regulator (LCAP), and fixed off-time PWM current control. It supports Hall sensor-based 120° commutation and provides synchronous rectification, thermal shutdown, and motor lead short-to-ground protection for industrial BLDC motor drives.

For engineers reviewing the A3938SLQTR datasheet, A3938SLQTR pinout, A3938SLQTR application, or A3938SLQTR equivalent, key selection criteria include its 38-pin TSSOP-LD package, adjustable dead time via DEAD pin, user-configurable fast/slow decay modes, bootstrap capacitor charge monitoring, and compatibility with external sensing resistors for precise peak current limiting (ITRIP = VREF / RSENSE).

Technical Context

The A3938SLQTR implements Hall-input-driven commutation logic for 120°-spaced sensors and integrates a bootstrapped high-side driver architecture to support N-channel power MOSFETs without requiring external high-voltage level shifters. Its internal fixed off-time PWM current regulation uses an external RC network on the RC pin to set t_OFF (10–50 µs), while blanking circuitry suppresses sense transients during MOSFET turn-on.

Protection features include real-time bootstrap capacitor charging current monitoring (trip at –9 mA), VREG undervoltage lockout (9.1–10.2 V), thermal shutdown at 165°C with 10°C hysteresis, and motor lead short-to-ground detection (V_DSH > 2.0 V). The FAULT pin reports open-drain fault status for invalid Hall codes, thermal events, VREG UVLO, or short-to-ground conditions.

Key Specifications

Pinout & Package

38-pin TSSOP-LD package (JEDEC MO-153 BD-1 compliant), 0.5 mm pitch, lead-free with 100% matte tin plated leadframe. Exposed thermal pad recommended for PCB thermal relief.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STSPIN32F0A and TMC6300-LA, the A3938SLQTR delivers plug-and-play Hall-based commutation with analog current limiting and integrated protection - reducing firmware overhead and external component count for cost-sensitive, high-reliability BLDC applications.

Availability

A3938SLQTR is available at Aetrix Electronics and suitable for industrial HVAC blower control, automotive power seat actuation, medical infusion pump drives, robotics joint actuators, and precision fan speed regulation requiring stable component supply and long-term manufacturability.

Supply support for A3938SLQTR 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 Manchester, NH.

The A3938 product line delivers robust, Hall-sensor-based three-phase BLDC motor controllers optimized for industrial, automotive, and medical motion systems where reliability, thermal resilience, and analog current regulation are critical.

FAQ

What is the maximum motor supply voltage supported by the A3938SLQTR?

The A3938SLQTR supports a maximum motor supply voltage (VBB) of 50 V, as specified in its Absolute Maximum Ratings. This rating applies continuously under normal operating conditions and enables direct integration into 12 V, 24 V, and 48 V BLDC motor systems. For 12 V applications, VBB must be shorted to VREG while maintaining VREG ≤ 15 V to avoid device damage.

How does the A3938SLQTR implement current limiting, and what components are required?

The A3938SLQTR implements peak current limiting using an internal fixed off-time PWM comparator that compares the voltage across an external sense resistor (connected to SENSE) against a reference voltage applied to REF. The trip current is calculated as I_TRIP = V_REF / R_SENSE. Required external components include the sense resistor, REF-setting voltage source (e.g., DAC or divider), and RC network on the RC pin to set off-time duration (10–50 µs).

Does the A3938SLQTR support both fast and slow current decay modes, and how is this selected?

Yes, the A3938SLQTR supports both fast and slow current decay modes via the MODE pin. When MODE = 0, fast decay is enabled (both high- and low-side FETs turn off during PWM off-cycle); when MODE = 1, slow decay is enabled (only the high-side FET turns off, allowing low-side conduction). The MODE pin has an internal 50 kΩ pull-up to LCAP, so a logic low must be actively driven to select fast decay.

What protection features are integrated into the A3938SLQTR, and how are faults reported?

The A3938SLQTR integrates bootstrap capacitor charge monitoring, VREG undervoltage lockout (9.1–10.2 V), thermal shutdown (165°C), Hall sensor code validation (rejects 000/111), and motor lead short-to-ground detection. All faults assert the open-drain FAULT pin low; only the short-to-ground fault is latched and cleared automatically at each commutation step. Other faults clear once the condition is resolved and RESET is toggled.

Can the A3938SLQTR drive N-channel MOSFETs exclusively, and what is required for high-side operation?

Yes, the A3938SLQTR is designed specifically to drive N-channel MOSFETs on both high- and low-sides. High-side operation relies on an integrated bootstrapped driver architecture: each high-side output (GHA/GHB/GHC) connects to a dedicated bootstrap capacitor (CA/CB/CC), which is charged through the corresponding low-side FET and motor winding when the low-side is active. No external high-voltage level shifters or P-channel devices are needed.