Allegro MicroSystems A3982SLBTR

Overview

A3982SLBTR from Allegro MicroSystems is a DMOS bipolar stepper motor driver IC with integrated translator, designed for full- and half-step excitation of bipolar stepper motors up to ±2 A per phase and 35 V supply. It features automatic mixed/slow current decay selection, synchronous rectification, and fixed off-time PWM current regulation. Used in precision motion control systems such as industrial automation actuators and medical infusion pumps.

For engineers reviewing the A3982SLBTR datasheet, A3982SLBTR pinout, A3982SLBTR application, or A3982SLBTR equivalent, key selection criteria include its 24-pin SOICW (LB) package with fused PGND leads, ±2 A output capability, 30 μs typical fixed off-time, and translator-based STEP/DIR interface requiring no phase sequencing logic.

Technical Context

The A3982SLBTR integrates two independent N-channel DMOS full-bridge drivers with dedicated current-sense inputs (SENSE1/SENSE2), reference-controlled DACs, and automatic decay-mode selection logic that evaluates step direction to assign slow or mixed decay per phase. Its translator interprets STEP/DIR/MS1 inputs to sequence microstep currents without external firmware.

Internal charge pump (CP1/CP2/VCP) enables high-side gate drive above VBB; VREG supplies sink-side logic; ROSC sets fixed off-time (~30 μs with 25 kΩ); and synchronous rectification reduces power dissipation by replacing body-diode conduction with low-R_DS(on) FET paths during decay.

Key Specifications

Pinout & Package

Package: 24-pin wide-body SOIC (suffix LB), with internally fused PGND leads (pins 6/7 and 18/19) for enhanced thermal dissipation and reduced ground impedance.

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 A3982SLBTR uniquely combines translator-based simplicity, ±2 A drive strength, and automatic decay adaptation-making it optimal for resource-constrained embedded systems needing reliable full/half-step motion without firmware complexity.

Availability

A3982SLBTR is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory analyzers, and 3D printer extruder control requiring stable component supply and long-term production continuity.

Supply support for A3982SLBTR 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 sensing and power ICs, founded in 1989 and headquartered in Worcester, Massachusetts.

The A3982 product line delivers integrated stepper motor drivers with on-chip translators for simplified motion control in cost-sensitive, space-constrained industrial and medical equipment where minimal MCU intervention is required.

FAQ

What is the maximum motor supply voltage supported by the A3982SLBTR?

The A3982SLBTR supports a maximum load supply voltage (VBB) of 35 V, as specified in its Absolute Maximum Ratings. This allows direct interfacing with common 24 V industrial power rails while retaining headroom for inductive kickback suppression. Operation above 35 V risks permanent damage to the DMOS output stages. The A3982SLBTR must be used with appropriate input capacitance and transient voltage suppression when deployed in noisy environments.

How does the A3982SLBTR determine whether to use Slow or Mixed decay mode?

The A3982SLBTR determines decay mode automatically per phase by comparing the DAC output level before and after each STEP pulse. If the new DAC level is higher than the previous, it selects Slow decay; if lower, it selects Mixed decay (31.25% fast decay followed by slow decay). This logic is implemented entirely within the A3982SLBTR's internal control block and requires no external configuration. The behavior is confirmed in the Functional Description section of the Allegro datasheet.

Can the A3982SLBTR operate with a 3.3 V logic supply?

Yes, the A3982SLBTR supports a logic supply voltage (VDD) range of 3.0 V to 5.5 V, making it fully compatible with 3.3 V microcontrollers. Input thresholds are referenced to VDD (e.g., VIN(1) ≥ 0.7×VDD), and input hysteresis (150–500 mV) ensures noise immunity. The A3982SLBTR maintains full functionality-including STEP, DIR, MS1, ENABLE, and RESET interpretation-at 3.3 V, with typical logic supply current of 5–8 mA depending on PWM frequency.

What is the purpose of the fused PGND pins on the A3982SLBTR package?

The A3982SLBTR's 24-pin SOICW (LB) package fuses PGND pins 6/7 and 18/19 internally to reduce ground path impedance and improve thermal conduction from the die to the PCB. This design lowers effective R_θJA to 35 °C/W on a 4-layer JEDEC board and supports continuous 2 A per phase operation without external heatsinking. The fused structure is a mechanical feature of the LB package-not a user-configurable option-and is documented in Allegro's package drawings and Selection Guide.

Does the A3982SLBTR require external Schottky diodes for flyback protection?

No, the A3982SLBTR does not require external Schottky diodes due to its integrated synchronous rectification feature. During current decay, the A3982SLBTR actively turns on low-R_DS(on) DMOS FETs instead of relying on body diodes, reducing power loss and eliminating reverse recovery issues. This capability is explicitly stated in the Features and Benefits section and Functional Description of the datasheet. External diodes may still be used for additional transient suppression but are not necessary for basic operation.