Allegro MicroSystems A3973SLBTR

Overview

A3973SLBTR from Allegro MicroSystems is a dual DMOS full-bridge PWM motor driver designed for bipolar microstepping stepper motor control, supporting ±1 A continuous output current at up to 35 V supply, with two independent 6-bit linear DACs for precise current regulation and programmable mixed/fast/slow decay modes.

For engineers reviewing the A3973SLBTR datasheet, A3973SLBTR pinout, A3973SLBTR application, or A3973SLBTR equivalent, this page provides verified technical context, real-world design meanings of key specs, validated pin functions, confirmed alternative options, and supply-ready procurement details - all grounded in Allegro's official documentation and electrical characterization data.

Technical Context

The A3973SLBTR integrates two independent H-bridges, each controlled by a dedicated 6-bit linear DAC (1.56% resolution steps) and programmable fixed-off-time PWM timer, enabling microstepping down to 1/64-step via external sequencing logic. Its internal 4 MHz oscillator (±25% typical accuracy) or external clock input supports configurable blank time (4–12/fOSC), off-time (1.75–63.75 μs), and fast-decay duration (1.75–31.75 μs).

Synchronous rectification operates in four selectable modes (active, passive, disabled, low-side-only) using low R_DS(on) DMOS outputs (0.54 Ω typ.), eliminating need for external clamp diodes in most configurations. Internal thermal shutdown (165°C, 15°C hysteresis), UVLO (4.2 V enable threshold), and crossover-current protection ensure robust operation without special power-up sequencing.

Key Specifications

Pinout & Package

Package: 24-pin SOICW (LB) with internally fused leads at pins 6, 7, 18, and 19 for enhanced thermal dissipation (2.2 W max). 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 H-bridge microstepping motor driver applications.

Compared with TB6600HG and DRV8825, the A3973SLBTR uniquely delivers dual independent microstepping bridges with serial-programmable DACs, decay modes, and synchronous rectification in a single SOICW package - making it optimal for compact, multi-axis systems demanding quiet, thermally efficient, and software-tunable motor control.

Availability

A3973SLBTR is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory equipment, and 3D printer axis control requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for A3973SLBTR 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 sensors and power ICs, headquartered in Worcester, Massachusetts, with over 40 years of analog/mixed-signal expertise.

The A3973SLBTR belongs to Allegro's motor driver product line, engineered specifically for precision bipolar stepper motor control in industrial automation, medical devices, and instrumentation where microstepping fidelity, thermal efficiency, and configurability are critical.

FAQ

What is the maximum continuous output current supported by the A3973SLBTR?

The A3973SLBTR supports ±1.0 A continuous output current per H-bridge at up to 35 V supply voltage. This rating assumes proper PCB thermal design with the SOICW package's fused leads (pins 6, 7, 18, 19) connected to a low-thermal-resistance ground plane. Exceeding this current without adequate heatsinking risks triggering thermal shutdown at 165°C junction temperature.

Does the A3973SLBTR include an internal oscillator, and can it be overridden?

Yes, the A3973SLBTR features a 4 MHz internal oscillator with ±25% typical accuracy. It can be overridden by applying an external clock signal to the OSC pin and selecting external mode via serial control bits D12–D13. The internal divider supports external clock frequencies divided by 1, 2, or 4, allowing system-level clock synchronization while retaining full PWM timing programmability.

How does the A3973SLBTR implement current regulation for microstepping?

The A3973SLBTR uses two independent 6-bit linear DACs (one per bridge) to generate reference voltages that set peak current via I_TRIP = V_DAC/(Range × R_S). With 64 discrete levels and 1.56% step resolution, it enables precise torque control across microstepping waveforms. The DAC output is buffered and trimmed to ±½ LSB total error, referenced to either the internal 2.0 V bandgap or an external ≤3 V source.

What protection features are built into the A3973SLBTR?

The A3973SLBTR integrates thermal shutdown (165°C, 15°C hysteresis), undervoltage lockout (UVLO active below 4.2 V on VDD), crossover-current protection, and internal transient-suppression diodes. These operate autonomously without external components. Notably, no special power-up sequencing is required - the device resets safely on VDD ramp-up and disables outputs during fault conditions until cleared.

Is the A3973SLBTR pin-compatible with other packages in the A3973 family?

Yes, the A3973SLBTR (SOICW LB package) is electrically identical to the A3973SB-T (DIP B package); both share the same 24-pin pinout, functionality, and timing specifications. Mechanical differences - such as fused leads in the LB variant versus batwing tabs in the B variant - do not affect electrical interoperability, enabling drop-in replacement in layouts designed for thermal or assembly constraints.