Allegro MicroSystems A3967SLB-T

Overview

A3967SLB-T from Allegro MicroSystems is a bipolar stepper motor driver IC with integrated translator, supporting full-, half-, quarter-, and eighth-step microstepping modes. It delivers ±750 mA output current at up to 30 V supply, features fixed off-time PWM current regulation with automatic mixed/fast/slow decay selection, and is used in precision motion control systems such as industrial automation actuators and medical infusion pumps.

For engineers reviewing the A3967SLB-T datasheet, A3967SLB-T pinout, A3967SLB-T application, or A3967SLB-T equivalent, key selection criteria include its 24-pin SOIC-LB package with fused thermal pins, step resolution control via MS1/MS2 logic inputs, PFD-based decay mode configuration, and built-in UVLO, thermal shutdown, and crossover-current protection.

Technical Context

The A3967SLB-T integrates a digital translator that converts STEP/DIR/MS1/MS2 logic commands into precise DAC-controlled phase currents, eliminating need for external sequencing tables. Its dual full-bridge outputs use Satlington® sink drivers and support independent RC-timed fixed off-time (30–46 µs) and blanking (700–1200 ns) per bridge.

Current regulation relies on external sense resistors (RS) and a programmable VREF input (1.0–VCC), with ITRIPmax = VREF/(8×RS). Decay mode selection is dynamic: slow decay for increasing current steps, and PFD-voltage-dependent fast/mixed decay for decreasing steps-reducing BEMF-induced waveform distortion and audible noise.

Key Specifications

Pinout & Package

Package: 24-pin SOIC with internally fused thermal pins (6, 7, 18, 19) at ground potential-no insulation required. Leads are lead-free with 100% matte tin plating.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar stepper motor driver applications.

Compared with TB6600HG and DRV8825, the A3967SLB-T uniquely combines translator integration, PFD-based adaptive decay, and fused thermal grounding-making it optimal for noise-sensitive, thermally constrained, or resource-limited embedded motion systems.

Availability

A3967SLB-T is available at Aetrix Electronics and suitable for industrial automation actuators, medical infusion pumps, lab equipment positioners, and 3D printer extruder drives requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for A3967SLB-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 Manchester, NH.

The A3967 product line delivers fully integrated stepper motor drivers with on-chip translators-designed specifically for embedded motion control applications where MCU resources are limited and acoustic/thermal performance is critical.

FAQ

What microstepping resolutions does the A3967SLB-T support, and how are they selected?

The A3967SLB-T supports full-, half-, quarter-, and eighth-step microstepping. Resolution is selected using the MS1 and MS2 logic inputs per the truth table: MS1=L/MS2=L = full step; MS1=H/MS2=L = half step; MS1=L/MS2=H = quarter step; MS1=H/MS2=H = eighth step. These inputs are latched on the rising edge of the next STEP pulse, so changes take effect only after a new step command. The A3967SLB-T implements this entirely within its integrated translator-no external sequencing logic is required.

How does the A3967SLB-T manage current decay modes, and what is the role of the PFD pin?

The A3967SLB-T automatically selects current decay mode per step transition: slow decay for increasing current steps, and PFD-voltage-dependent decay for decreasing steps. The PFD (Percent Fast Decay) pin accepts a DC voltage between 0.21VCC and 0.6VCC to set mixed-decay ratio-below 0.21VCC forces fast decay, above 0.6VCC forces slow decay. This adaptive behavior minimizes BEMF-induced current distortion, directly improving step accuracy and reducing audible noise. The A3967SLB-T's PFD architecture is distinct from fixed-decay drivers and enables optimized performance across varying motor loads and speeds.

What thermal advantages does the A3967SLB-T's 24-pin SOIC-LB package provide?

The A3967SLB-T's SOIC-LB package fuses pins 6, 7, 18, and 19 internally to the power tab, creating low-impedance thermal paths to PCB ground planes. This reduces junction-to-ambient thermal resistance to 35°C/W on JEDEC-standard 4-layer boards-20°C/W lower than conventional SOIC packages. The fused pins operate at ground potential and require no insulation, simplifying layout. This design allows the A3967SLB-T to sustain ±750 mA output continuously at 85°C ambient without derating, unlike non-fused alternatives that require heatsinking or current reduction above 60°C.

Can the A3967SLB-T operate with a 3.3 V logic supply, and what is its minimum VCC requirement?

Yes, the A3967SLB-T operates with a 3.3 V logic supply-the specified VCC range is 3.0 V to 5.5 V. Its undervoltage lockout (UVLO) activates below 2.45 V (typical), ensuring reliable reset behavior during brown-out conditions. At 3.3 V, all logic inputs (STEP, DIR, MS1, MS2, etc.) meet valid thresholds: VIN(1) ≥ 2.31 V and VIN(0) ≤ 0.99 V. The A3967SLB-T's 3.3 V compatibility eliminates level-shifting requirements in modern low-voltage embedded systems, and its 20 µA sleep current further extends battery life in portable applications using the A3967SLB-T.

What protection features are built into the A3967SLB-T, and do they require external components?

The A3967SLB-T integrates thermal shutdown (165°C trigger, 15°C hysteresis), undervoltage lockout (2.7 V enable threshold), and crossover-current protection-all implemented internally with no external components required. Thermal shutdown disables all outputs until junction temperature falls below 150°C; UVLO holds the translator in home state and disables drivers until VCC rises above threshold; crossover protection prevents shoot-through during bridge switching. These functions operate autonomously-special power-up sequencing, external watchdogs, or discrete protection circuits are unnecessary. The A3967SLB-T's robustness makes it suitable for unattended industrial and medical deployments where reliability is paramount.