Allegro MicroSystems A3973SB

Overview

A3973SB 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 integrated 6-bit linear DACs for precise torque control and programmable mixed/fast/slow current-decay modes. It operates with a 4 MHz internal oscillator and supports serial-interface configuration via CLOCK/DATA/STROBE lines.

For engineers reviewing the A3973SB datasheet, A3973SB pinout, A3973SB application, or A3973SB equivalent, key selection criteria include its dual-bridge architecture, 24-pin DIP package with batwing power tabs, synchronous rectification capability, thermal shutdown at 165°C, and compatibility with 3.3 V or 5 V logic inputs.

Technical Context

The A3973SB implements two independent PWM-controlled H-bridges, each with dedicated 6-bit linear DACs (0–63 steps, 1.56% resolution) referenced to an internal 2.0 V precision bandgap or external reference. Current regulation uses fixed-off-time PWM with programmable blank time (4–12/f_OSC) and off-time (1.75–63.75 μs at 4 MHz).

Its serial interface accepts two 19-bit words for full configuration: Word 0 sets DAC values, phase, decay mode, reference source, and Gm range (×4 or ×8); Word 1 configures blank time, off-time, fast-decay duration, oscillator control, and synchronous rectification mode (Active/Passive/Disabled/Low-side-only).

Key Specifications

Pinout & Package

Package: 24-pin DIP (Package B) with two copper batwing power tabs at ground potential - optimized for vertical mounting and direct PCB heatsinking without 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 uniquely delivers dual independent 6-bit DAC-controlled bridges in a single DIP package with synchronous rectification and 4 MHz self-timed PWM - enabling compact, low-noise, software-tunable microstepping without external analog support circuitry.

Availability

A3973SB is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory analyzers, and 3D printer extruder control requiring stable component supply and long-term production continuity.

Supply support for A3973SB 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 sensors and power ICs, headquartered in Worcester, Massachusetts, with focus on motion control, energy efficiency, and reliability-critical applications.

The A3973SB belongs to Allegro's dual-bridge stepper driver product line, engineered specifically for bipolar microstepping motors in space-constrained industrial and medical equipment where precision torque control and thermal efficiency are paramount.

FAQ

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

The A3973SB supports ±1.0 A continuous output current per bridge under specified thermal conditions (T_A ≤ 85°C, adequate heatsinking). This rating assumes use of the batwing power tabs in the 24-pin DIP package and adherence to the absolute maximum junction temperature of 150°C. Exceeding this current without enhanced cooling will trigger thermal shutdown at 165°C.

Does the A3973SB require an external clock source, or does it have an internal oscillator?

The A3973SB includes a 4 MHz internal oscillator that requires no external components - the OSC pin can be grounded for default operation. For higher frequency stability, an external clock (2.5–6.0 MHz) may be applied to the OSC pin, with internal dividers (÷1, ÷2, ÷4) selectable via serial interface bits D12–D13. The A3973SB datasheet confirms internal oscillator operation is fully functional without external parts.

How does the A3973SB implement microstepping current control?

The A3973SB implements microstepping via two independent 6-bit linear DACs (one per bridge), each setting current magnitude in 1.56% increments of full scale. DAC output feeds a precision current comparator referenced to either the internal 2.0 V bandgap or an external ≤3 V source. Combined with programmable decay modes and synchronous rectification, this enables smooth 1/2 to 1/64 microstepping without external DACs or op-amps.

What protection features are integrated into the A3973SB?

The A3973SB integrates thermal shutdown (165°C trip, 15°C hysteresis), undervoltage lockout (4.2 V VDD enable), crossover-current protection (300–900 ns dead time), and transient-suppression diodes. It also monitors VCP and VREG supply integrity - disabling outputs if either falls below safe operating thresholds. No special power-up sequencing is required.

Can the A3973SB drive two independent stepper motors, or is it limited to one 4-wire bipolar motor?

The A3973SB is designed to drive one standard 4-wire bipolar stepper motor using its two H-bridges (OUT1A/1B and OUT2A/2B), with independent current control per winding. While it cannot drive two *separate* motors due to shared logic supply, VBB rails, and serial interface, it fully supports advanced microstepping waveforms including full-step, half-step, and fractional microsteps up to 1/64 via coordinated DAC and phase programming.