Allegro MicroSystems A3973SB-T

Overview

A3973SB-T from Allegro MicroSystems is a dual DMOS full-bridge PWM motor driver designed for bipolar microstepping stepper motor control, delivering ±1 A continuous output current at up to 35 V supply, with two independent 6-bit linear DACs (1.56% resolution) and programmable mixed/fast/slow current-decay modes for precise torque control in motion systems.

For engineers reviewing the A3973SB-T datasheet, A3973SB-T pinout, A3973SB-T application, or A3973SB-T equivalent, this device supports serial-interface configuration of bridge phase, decay mode, synchronous rectification, blank time, and fixed off-time - critical for optimizing microstepping smoothness, thermal performance, and EMI in industrial automation and precision positioning.

Technical Context

The A3973SB-T integrates two independent H-bridges, each controlled by a dedicated 6-bit DAC and PWM timer with programmable fixed off-time (1.75–63.75 μs) and fast-decay portion (1.75–31.75 μs), enabling fine-grained current regulation per phase. Its internal 4 MHz oscillator (±25% typical accuracy) or external clock input provides timing flexibility.

Synchronous rectification operates in four configurable modes (Active, Passive, Disabled, Low-Side Only) using low R_DS(on) DMOS drivers (0.54 Ω typ.) to minimize power loss during current decay; internal VREG (5 V) powers sink-side drivers, while UVLO (4.2 V typ.) and thermal shutdown (165°C, 15°C hysteresis) ensure robust fault protection.

Key Specifications

Pinout & Package

Package: 24-pin DIP (Package B) with two copper batwing power tabs (pins 11, 12, 23, 24 internally connected to GROUND); power tabs are at ground potential and require no electrical isolation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-bridge microstepping PWM motor driver applications.

Compared with TB6600HG and DRV8825, the A3973SB-T uniquely combines serial programmability of decay timing, dual independent 6-bit DACs, and synchronous rectification in a through-hole DIP package - making it optimal for industrial motion systems requiring field-configurable microstepping behavior and thermal reliability at ±1 A.

Availability

A3973SB-T is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory equipment, and 3D printer extruder control requiring stable component supply, long-term lifecycle support, and through-hole manufacturability.

Supply support for A3973SB-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 of high-performance magnetic sensing and power ICs, founded in 1989 and headquartered in Worcester, Massachusetts.

The A3973SB-T belongs to Allegro's motor driver product line, engineered specifically for precision bipolar stepper motor control in industrial automation, medical devices, and instrumentation where reliability, programmability, and thermal robustness are critical.

FAQ

What is the maximum continuous output current supported by the A3973SB-T?

The A3973SB-T supports ±1.0 A continuous output current per bridge under specified thermal conditions (T_A ≤ 85°C, adequate heat sinking). This rating assumes use of the 24-pin DIP package with its two batwing ground tabs for thermal conduction. Exceeding this current may trigger thermal shutdown at 165°C junction temperature, and sustained operation above 1 A requires verification of PCB copper area and ambient airflow per Allegro Application Note AN29319.34.

Does the A3973SB-T require external Schottky diodes for flyback protection?

No, the A3973SB-T does not require external Schottky diodes in most applications due to its integrated synchronous rectification circuitry. When enabled (default Active mode), the device uses low R_DS(on) DMOS transistors to recirculate current during decay, bypassing body diodes and reducing power loss. External diodes are only needed if synchronous rectification is disabled via serial command - a configuration typically reserved for specific EMI or safety requirements.

How is microstepping resolution achieved with the A3973SB-T's 6-bit DAC?

The A3973SB-T achieves microstepping resolution through two independent 6-bit linear DACs (64 steps each), setting peak current per bridge as I_TRIP = V_DAC/(Range × R_S). With 1.56% per-step increment and programmable decay modes, it supports smooth current waveforms for 1/2-, 1/4-, 1/8-, 1/16-, and 1/32-step microstepping when paired with external indexer logic. The DAC code '0' disables the bridge, enabling true zero-current hold states.

Can the A3973SB-T operate with a 3.3 V logic supply?

Yes, the A3973SB-T accepts 3.3 V logic signals on its digital inputs (CLOCK, DATA, STROBE, SLEEP) as they are compatible with both 3.3 V and 5 V CMOS levels (V_IN(1) ≥ 2.0 V, V_IN(0) ≤ 0.8 V). However, the VDD pin must be supplied with 4.5–5.5 V to power internal regulators and reference circuitry - a level-shifter or separate 5 V rail is required if the host MCU runs at 3.3 V only.

What is the function of the MUX and REF pins on the A3973SB-T?

The MUX pin selects between internal and external reference sources based on the D17 bit in Word 0 of the serial interface; the REF pin accepts an external reference voltage (0.5–2.6 V) when D17 = 1, or connects to the internal 2.0 V bandgap reference when D17 = 0. This dual-reference architecture allows flexible current scaling - for example, using a precision 2.5 V reference with a 0.1 Ω sense resistor yields 3.125 A full-scale trip current, while the internal 2 V reference with 0.2 Ω gives 1.25 A.