Allegro MicroSystems A3967SLB

Overview

A3967SLB 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, employs fixed off-time PWM current regulation with automatic mixed/fast/slow decay selection, and targets motion control in compact industrial actuators, lab automation stages, and precision fluid handling systems.

For engineers reviewing the A3967SLB datasheet, A3967SLB pinout, A3967SLB application, or A3967SLB 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 selection, and built-in UVLO, thermal shutdown, and crossover-current protection.

Technical Context

The A3967SLB integrates a digital translator that converts STEP/DIR/MS1/MS2 logic commands into precise DAC-controlled phase currents without external sequencing tables. Its dual full-bridge output stage uses Satlington® sink drivers and supports independent RC timing (RC1/RC2) for fixed off-time control per bridge.

Current regulation relies on external sense resistors (SENSE1/SENSE2) and a reference voltage (REF), with ITRIPmax = VREF/(8 × RS). Decay mode is dynamically selected per step transition: slow decay for increasing current, and fast/mixed decay-governed by PFD voltage thresholds (0.21VCC and 0.6VCC)-for decreasing current, minimizing BEMF-induced waveform distortion.

Key Specifications

Pinout & Package

Package: 24-pin SOIC with internally fused thermal pins (6, 7, 18, 19) at ground potential - provides enhanced thermal dissipation (RθJA = 35°C/W on 4-layer PCB) without requiring insulated mounting.

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 uniquely combines translator simplicity, fused-pin thermal reliability, and analog PFD-based decay tuning - making it optimal for space-constrained, noise-sensitive industrial motion systems requiring minimal firmware integration.

Availability

A3967SLB is available at Aetrix Electronics and suitable for lab automation stages, industrial valve actuators, and desktop CNC routers requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for A3967SLB 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, specializing in motion control, current sensing, and automotive-grade interface solutions.

The A3967SLB belongs to Allegro's microstepping driver product line, engineered for embedded motion systems where ease of integration, thermal resilience, and silent operation outweigh raw current headroom.

FAQ

What microstep resolutions does the A3967SLB support, and how are they selected?

The A3967SLB supports full-, half-, quarter-, and eighth-step microstepping modes. Selection is performed exclusively via the logic states of MS1 and MS2 pins, as defined in the truth table (e.g., MS1=H/MS2=H enables eighth-step). The translator automatically sequences DAC outputs and adjusts decay mode per step - no firmware or external sequencing logic is required. This behavior is intrinsic to the A3967SLB silicon design and verified across all operating conditions.

How does the A3967SLB handle thermal management, and what is the role of pins 6, 7, 18, and 19?

The A3967SLB uses four internally fused pins (6, 7, 18, 19) connected directly to the exposed thermal pad of its 24-pin SOIC-LB package. These pins are at ground potential and must be soldered to a solid PCB ground plane to achieve RθJA = 35°C/W (4-layer JEDEC board). This fused-pin architecture reduces thermal resistance by ~40% versus standard SOIC, enabling sustained ±750 mA operation without external heatsinks - a key differentiator of the A3967SLB in thermally constrained designs.

Can the A3967SLB operate with a 3.3 V logic supply, and what are the implications for STEP signal timing?

Yes, the A3967SLB supports 3.0–5.5 V logic supply (VCC), fully compatible with 3.3 V microcontrollers. At 3.3 V, the minimum STEP pulse width remains 1.0 µs and data setup/hold times are 200 ns - all guaranteed per datasheet. The STEP input threshold is referenced to VCC (VIN(1) = 0.7VCC, VIN(0) = 0.3VCC), ensuring noise-immune switching. No level-shifting circuitry is needed, simplifying interface design for the A3967SLB in mixed-voltage systems.

What protection features are integrated into the A3967SLB, and how do they respond to fault conditions?

The A3967SLB integrates three hardware protections: undervoltage lockout (UVLO) triggers below 2.45 V (typ.), thermal shutdown activates at 165°C (typ.) with 15°C hysteresis, and crossover-current protection prevents shoot-through during H-bridge switching. During UVLO or thermal fault, all outputs disable and the translator resets to home state. These functions require no external components and are active at power-up - critical for reliable operation of the A3967SLB in unattended industrial equipment.

How does the PFD pin affect motor performance, and what voltage range yields mixed-decay operation on the A3967SLB?

The PFD pin on the A3967SLB sets the fast-decay portion of mixed-decay mode. When the PFD voltage is between 0.21VCC and 0.6VCC, the device enters mixed-decay - transitioning from fast decay (to quickly reduce current) to slow decay (to minimize ripple) within the fixed off-time window. This dynamic balance reduces audible noise and improves step accuracy. Voltages outside this range force pure fast (below 0.21VCC) or slow (above 0.6VCC) decay - a unique analog control feature of the A3967SLB not found in most competing drivers.