Allegro MicroSystems A3984SLP

Overview

A3984SLP from Allegro MicroSystems is a DMOS bipolar stepper motor driver IC with integrated step translator, supporting full-, half-, quarter-, and sixteenth-step modes. It delivers ±2 A output current per bridge at up to 35 V supply, features automatic mixed/slow decay selection, synchronous rectification, and operates from a 3.0–5.5 V logic supply. It is used in precision motion control systems such as industrial automation actuators and medical fluid pumps.

For engineers reviewing the A3984SLP datasheet, A3984SLP pinout, A3984SLP application, or A3984SLP equivalent, key selection considerations include its fixed off-time PWM current regulation (20–40 µs), 24-pin TSSOP-LP package with exposed thermal pad, microstep resolution control via MS1/MS2 inputs, and built-in protection including thermal shutdown (165°C) and UVLO (2.7 V typical).

Technical Context

The A3984SLP integrates dual N-channel DMOS full-bridge drivers with independent current-sense regulation per phase, controlled by an on-chip DAC-driven translator. Its fixed off-time PWM circuit uses external ROSC (25 kΩ typical) to set t_OFF ≈ 30 µs and internal blanking (~1 µs) to suppress false overcurrent detection during switching transients.

Decay mode selection is fully automatic: slow decay for increasing phase current, mixed decay (31.25% fast + 68.75% slow) for decreasing current - minimizing audible noise and improving step accuracy. Synchronous rectification replaces body-diode conduction with low-R_DS(ON) FET paths, reducing power dissipation without requiring external Schottky diodes.

Key Specifications

Pinout & Package

Package: 24-pin TSSOP with exposed thermal pad (LP suffix), 1.2 mm max height, lead-free with 100% matte tin plating. Requires external 0.1 µF CP1–CP2, 0.1 µF VCP–VBB, and 0.22 µF VREG–GND capacitors.

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 A3984SLP uniquely combines translator-based simplicity, automatic decay adaptation, and robust thermal/UVLO protection in a single 24-pin LP package - reducing BOM count and firmware overhead for embedded motion control.

Availability

A3984SLP is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory analyzers, and ATM cash dispensers requiring stable component supply and long-term production continuity.

Supply support for A3984SLP 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 IC solutions, founded in 1985 and headquartered in Manchester, NH.

The A3984SLP belongs to Allegro's DMOS stepper driver product line, engineered specifically for compact, high-efficiency bipolar stepper control in space-constrained industrial and medical equipment.

FAQ

What is the maximum motor supply voltage supported by the A3984SLP?

The A3984SLP supports a load supply voltage (VBB) range of 8 V to 35 V. Absolute maximum rating is 35 V - exceeding this may cause permanent damage. Operation below 8 V is not guaranteed due to internal charge pump and regulator constraints. The A3984SLP is commonly used with 12 V or 24 V stepper motor supplies in industrial motion systems.

How does the A3984SLP determine current decay mode during stepping?

The A3984SLP automatically selects decay mode based on the direction of DAC output change at each STEP pulse: slow decay is used when phase current increases; mixed decay (31.25% fast + 68.75% slow) is used when phase current decreases. This behavior is intrinsic to the A3984SLP's internal control logic and requires no external configuration - improving microstep smoothness and reducing audible noise.

Can the A3984SLP operate with a 3.3 V logic supply?

Yes, the A3984SLP accepts a logic supply (VDD) from 3.0 V to 5.5 V, making it fully compatible with 3.3 V microcontrollers. All logic inputs (STEP, DIR, MS1, MS2, ENABLE, RESET, SLEEP) have thresholds referenced to VDD, with 150–500 mV hysteresis. No level-shifting circuitry is needed when interfacing the A3984SLP to 3.3 V systems.

What external components are mandatory for stable A3984SLP operation?

Four external capacitors are mandatory: 0.1 µF between CP1–CP2, 0.1 µF between VCP–VBB, 0.22 µF between VREG–GND, and a resistor (e.g., 25 kΩ) from ROSC to GND. Additionally, two current-sense resistors (RS1, RS2) must be placed between SENSE1/SENSE2 and GND. Failure to install these components will result in improper charge pump operation, unstable regulation, or current limit malfunction in the A3984SLP.

Does the A3984SLP require special PCB layout considerations?

Yes - the A3984SLP's 24-pin TSSOP-LP package includes an exposed thermal pad that must be soldered to a large copper ground plane with ≥4 thermal vias (0.3 mm diameter, spaced ≤1.2 mm apart). The GND pins (13 and 24) must be shorted externally to this pad. Poor thermal layout risks exceeding the 150°C junction limit under ±2 A load, triggering thermal shutdown and disrupting motor operation.