Allegro MicroSystems A3984SLPTR

Overview

A3984SLPTR from Allegro MicroSystems is a DMOS bipolar stepper motor driver IC with integrated step translator, supporting full-, half-, quarter-, and sixteenth-step modes, 35 V load supply, ±2 A output current, and automatic mixed/slow decay selection for reduced audible noise and improved microstep accuracy in motion control systems.

For engineers reviewing the A3984SLPTR datasheet, A3984SLPTR pinout, A3984SLPTR application, or A3984SLPTR equivalent, this page delivers verified technical context, real-world design meaning of key specs, validated pin functions, and two confirmed alternative parts for motion control subsystems requiring compact, self-contained microstepping drive.

Technical Context

The A3984SLPTR integrates a digital translator that converts STEP/DIR inputs into precise phase current waveforms without external sequencing logic. Its fixed off-time PWM current regulation uses external ROSC (25 kΩ typical) to set t_OFF ≈ 30 µs and internal DACs to scale I_TRIP from 0% to 100% of I_TRIPMAX in 256 steps per phase.

Each of the two DMOS full-bridges features synchronous rectification, blanking (t_BLANK ≈ 1 µs), and crossover-current protection. Decay mode-Slow or Mixed (31.25% fast + 68.75% slow)-is selected automatically per step based on DAC output direction, minimizing back-EMF distortion and power dissipation.

Key Specifications

Pinout & Package

Package: 24-pin TSSOP with exposed thermal pad (LP suffix), 0.65 mm pitch, 7.8 × 4.4 mm body, 1.2 mm max height. Thermal pad must be soldered to PCB ground plane with ≥4 thermal vias (0.3 mm diameter) for reliable 2 A operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TB6600HG and DRV8825, the A3984SLPTR uniquely combines translator simplicity, automatic decay adaptation, and robust 2 A drive in a thermally enhanced TSSOP package-making it optimal for embedded motion systems where MCU resources are constrained and acoustic performance matters.

Availability

A3984SLPTR is available at Aetrix Electronics and suitable for 3D printer motion control, CNC milling axis drivers, and automated lab equipment requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for A3984SLPTR 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 motor driver solutions for industrial and automotive markets.

The A3984 product line delivers fully integrated stepper drivers with on-chip translators and adaptive current regulation-designed specifically for resource-constrained embedded systems needing plug-and-play microstepping without firmware development.

FAQ

What is the maximum motor supply voltage supported by the A3984SLPTR?

The A3984SLPTR supports a load supply voltage (VBB) up to 35 V, as specified in its Absolute Maximum Ratings. Operation above this voltage risks permanent damage to the DMOS output transistors. For reliable 2 A continuous current delivery, VBB should be maintained between 8 V and 35 V, with thermal design accounting for power dissipation at higher voltages and currents.

How does the A3984SLPTR determine whether to use Slow or Mixed decay mode?

The A3984SLPTR determines decay mode per step by comparing the new DAC output level against the previous level for each phase. If the DAC output increases (indicating higher target current), it selects Slow decay; if it decreases (lower target current), it selects Mixed decay-initially fast for 31.25% of t_OFF, then slow for the remainder. This logic is implemented entirely in hardware and requires no external configuration.

Can the A3984SLPTR operate with a 3.3 V logic supply?

Yes, the A3984SLPTR accepts VDD from 3.0 V to 5.5 V, making it fully compatible with 3.3 V microcontrollers and FPGA I/O banks. All logic inputs (STEP, DIR, MS1, MS2, RESET, ENABLE, SLEEP) have guaranteed switching thresholds referenced to VDD, with 150–500 mV hysteresis to ensure noise immunity in mixed-voltage systems.

What is the purpose of the ROSC pin on the A3984SLPTR?

The ROSC pin sets the fixed off-time (t_OFF) of the internal PWM current regulator. Connecting a resistor from ROSC to GND determines t_OFF ≈ ROSC / 825 (µs); a 25 kΩ resistor yields ~30 µs. If ROSC is tied to VDD (>3 V), t_OFF defaults to 30 µs. This timing directly affects current regulation stability and thermal performance at high step rates.

Is thermal vias required for the exposed pad on the A3984SLPTR LP package?

Yes-thermal vias under the exposed pad are strongly recommended for any application drawing ≥1.5 A per bridge. The datasheet specifies R_θJA = 28°C/W assumes a 4-layer PCB with thermal vias. Without them, junction temperature rise increases significantly, risking thermal shutdown during sustained 2 A operation. At least four 0.3 mm vias connected to a solid ground plane are advised.