Allegro MicroSystems A3964SLBTR

Overview

A3964SLBTR from Allegro MicroSystems is a dual full-bridge PWM motor driver IC designed for bipolar stepper motor current control via fixed off-time PWM. It delivers ±800 mA continuous output current per bridge, supports up to 30 V load supply voltage, and integrates a precision 2.5 V reference for accurate peak-current regulation in motion control systems.

For engineers reviewing the A3964SLBTR datasheet, A3964SLBTR pinout, A3964SLBTR application, or A3964SLBTR equivalent, key selection considerations include its internal PWM current control architecture, RC-tunable off-time (27–33 μs typical), crossover-current protection, thermal shutdown at 165°C, and SOIC-20 LB package with internally fused power pins.

Technical Context

The A3964SLBTR implements two independent full-bridge drivers with saturated sink/source output stages, each controlled by dedicated PHASE and ENABLE inputs. Its internal fixed off-time PWM circuit compares sensed current against a user-set VREF(IN) threshold, using external RS and resistor divider (RA/RB) to define ITRIP ≈ VREF(IN)/RS.

RC timing networks (RT/CT) set both the PWM off-time (tOFF = RT × CT) and comparator blanking window-eliminating need for external filtering on SENSE inputs. The device operates in slow-decay (2-quadrant) PWM mode and includes integrated clamp diodes, UVLO (4.40 V disable threshold), and 15°C thermal hysteresis.

Key Specifications

Pinout & Package

Package: 20-pin SOICW (suffix LB), lead-free with 100% matte tin plating; internally fused pins 5, 6, 15, and 16 enhance thermal dissipation from batwing power terminals.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TB6600HG and DRV8825, the A3964SLBTR offers unique integration of RC-tunable PWM timing, internal 2.5 V reference, and fused SOIC-20 LB packaging-making it optimal for cost-sensitive, thermally constrained bipolar stepper systems requiring ±800 mA and deterministic current regulation without microstepping.

Availability

A3964SLBTR is available at Aetrix Electronics and suitable for industrial motion control, medical device actuation, automated test equipment, and lab automation platforms requiring stable component supply and long-term manufacturability.

Supply support for A3964SLBTR 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.

The A3964SLBTR belongs to Allegro's legacy motor driver product line, engineered specifically for robust, low-component-count bipolar stepper and brushed DC motor control in industrial and medical environments.

FAQ

What is the maximum continuous output current supported by the A3964SLBTR?

The A3964SLBTR supports ±800 mA continuous output current per bridge under specified thermal conditions (TA ≤ 85°C, adequate PCB copper). This rating assumes proper heatsinking-exceeding 150°C junction temperature triggers thermal shutdown. Peak transient current may reach ±1.0 A for short durations (tw = 10 μs), but sustained operation above ±800 mA risks thermal violation. The A3964SLBTR's fused SOIC-20 LB package improves thermal dissipation versus standard SOIC.

How does the A3964SLBTR implement current regulation without an external PWM controller?

The A3964SLBTR uses an internal fixed off-time PWM current-control circuit that compares voltage across external sense resistors (RS) to a user-defined VREF(IN) threshold. When sensed current reaches ITRIP ≈ VREF(IN)/RS, the source driver turns off for a duration set by RT×CT. The A3964SLBTR then recirculates current through the sink driver and internal diode, repeating the cycle to maintain peak current. No external clock or PWM signal is required-the A3964SLBTR self-generates regulation.

Can the A3964SLBTR drive unipolar stepper motors?

No, the A3964SLBTR is designed exclusively for bipolar stepper motors and brushed DC motors. Its dual full-bridge topology requires four-terminal connection per winding and relies on PHASE/ENABLE sequencing to reverse current direction. Unipolar steppers use center-tapped windings and require different drive schemes (e.g., single-pole switching). Using the A3964SLBTR with unipolar motors would result in incorrect excitation and potential damage due to improper current paths.

What is the purpose of the RC timing network on pins RC1 and RC2 of the A3964SLBTR?

The RC network (RT and CT) on A3964SLBTR pins RC1 and RC2 serves two simultaneous functions: it sets the fixed PWM off-time (tOFF = RT × CT) and defines the comparator blanking window. During switching transitions-including PHASE changes, ENABLE toggles, or internal PWM reset-the A3964SLBTR blanks the current-sense comparator output to prevent false trips caused by diode reverse-recovery transients. This dual role eliminates need for separate timing and filtering components, reducing BOM count and layout complexity.

Does the A3964SLBTR require special power-up sequencing?

No, the A3964SLBTR does not require special power-up sequencing. Its internal circuitry ensures safe initialization regardless of VBB and VCC ramp order. The device incorporates UVLO protection that holds outputs disabled until VCC exceeds 4.375 V (typical), and thermal shutdown activates only if junction temperature exceeds 165°C. This makes the A3964SLBTR suitable for simple power-rail designs without complex supervisor ICs-ideal for cost-sensitive industrial and medical applications where the A3964SLBTR is deployed.