Allegro MicroSystems A3964SLB

Overview

A3964SLB from Allegro MicroSystems is a dual full-bridge PWM motor driver IC designed for bipolar stepper and bidirectional DC motor control, delivering ±800 mA continuous output current per bridge at up to 30 V load supply, with internal 2.5 V precision reference and user-configurable fixed off-time PWM current regulation via external RC networks.

For engineers reviewing the A3964SLB datasheet, A3964SLB pinout, A3964SLB application, or A3964SLB equivalent, this device supports precise peak-current control in motion systems requiring thermal robustness, crossover-current protection, and logic-level interface compatibility with 4.75–5.25 V supplies.

Technical Context

The A3964SLB implements two independent full-bridge outputs with saturated sink drivers and internal transconductance-based current sensing, where peak trip current (ITRIP) is set by VREF(IN)/RS and regulated via fixed off-time PWM with t_OFF = R_TC_T. Each bridge uses PHASE input to select current polarity and ENABLE to disable all drivers simultaneously.

Its functional block includes integrated 2.5 V reference (±50 mV accuracy), comparator blanking synchronized to PHASE/ENABLE transitions and RC timing, UVLO (4.40 V disable threshold), thermal shutdown (165°C, 15°C hysteresis), and internal clamp diodes - all operating without power-up sequencing requirements.

Key Specifications

Pinout & Package

A3964SLB is housed in a 20-lead wide-body plastic SOIC package with copper heat sink tabs at ground potential - no electrical isolation required; tab thermal resistance θ_JA = 60°C/W (unmounted), reduced by PCB copper area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with A3964SLB, A3966SLB offers identical footprint and interface but reduced current capability and no internal reference, while TB6600HG delivers higher current at the cost of increased design complexity and no integrated blanking or reference - making A3964SLB optimal for mid-power, space-constrained motion control.

Availability

A3964SLB is available at Aetrix Electronics and suitable for stepper positioning systems, bidirectional DC motor drives, industrial valve actuators, and medical infusion pump designs requiring stable component supply with long-term industrial lifecycle support.

Supply support for A3964SLB 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 semiconductor company specializing in high-performance magnetic sensing and power ICs, with over 40 years of motion control innovation.

The A3964SLB belongs to Allegro's dual full-bridge PWM motor driver product line, engineered specifically for bipolar stepper and reversible DC motor applications demanding integrated current regulation, thermal resilience, and minimal external component count.

FAQ

What is the maximum continuous output current supported by the A3964SLB?

The A3964SLB supports ±800 mA continuous output current per bridge at ambient temperatures up to +85°C with adequate PCB copper heatsinking. This rating assumes proper RC timing selection, 30 V VBB, and adherence to thermal limits - exceeding ±800 mA continuously risks triggering thermal shutdown or degrading long-term reliability. The A3964SLB datasheet specifies 1.0 A pulsed (10 µs) as absolute maximum.

Does the A3964SLB require external current-sense resistors, and how are they configured?

Yes, the A3964SLB requires two external current-sense resistors (RS1 and RS2), one per bridge, placed between each SENSE pin and ground. Peak current ITRIP is calculated as VREF(IN)/RS, where VREF(IN) is set via a resistor divider from the internal 2.5 V reference (VREF(OUT)). The A3964SLB datasheet recommends RS values that keep SENSE voltage ≤1.0 V and divider impedance between 3 kΩ and 15 kΩ for optimal accuracy.

Can the A3964SLB operate without an external RC timing network?

No - the A3964SLB requires external RC networks on RC1 and RC2 pins to define fixed off-time (t_OFF) and comparator blanking duration. Without these, PWM current regulation fails: the internal latch cannot reset, causing uncontrolled current rise and immediate thermal shutdown. Typical values are 30 kΩ and 1000 pF per channel, yielding ~30 µs t_OFF, as confirmed in the A3964SLB electrical characteristics table.

What thermal management considerations apply to the A3964SLB in SOIC-20 package?

The A3964SLB SOIC-20 package has θ_JA = 60°C/W (unmounted). To maintain TJ < 125°C at ±800 mA, at least 6 cm² of 2-oz copper connected to the ground and heat sink tabs is recommended. Thermal shutdown activates at 165°C (typical), with 15°C hysteresis. Direct thermocouple measurement on the copper tab (TTAB) allows junction estimation via TJ ≈ TTAB + (2 × ILOAD × VF × 6°C/W), where VF is from the A3964SLB datasheet.

Is the A3964SLB pin-compatible with the A3964SB DIP variant?

No - the A3964SLB (20-lead SOIC) and A3964SB (24-lead DIP) have different pin counts, layouts, and signal mappings. For example, A3964SLB uses pins 15–16 for ENABLE2/ENABLE1 and pins 4–5 for RC2/RC1, whereas A3964SB dedicates pins 23–24 to ENABLE1/ENABLE2 and pins 1–2 to RC1/RC2. PCB redesign is required for substitution; the A3964SLB datasheet explicitly states "different package styles" with distinct drawings PP-047-1 and PP-005-2.