Allegro MicroSystems A3984SLP-T

Overview

A3984SLP-T 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. It enables precise microstepping control in compact motion systems such as industrial automation actuators and medical lab equipment.

For engineers reviewing the A3984SLP-T datasheet, A3984SLP-T pinout, A3984SLP-T application, or A3984SLP-T equivalent, key selection criteria include its fixed off-time PWM current regulation (20–40 µs), synchronous rectification for low power dissipation, thermal shutdown at 165°C, and 24-pin TSSOP-LP package with exposed thermal pad.

Technical Context

The A3984SLP-T integrates dual DMOS full-bridge drivers, a DAC-based translator, and fixed off-time PWM current regulators per phase. Its decay mode logic automatically selects slow decay for increasing phase current and mixed decay (31.25% fast + remainder slow) for decreasing current, minimizing back-EMF distortion and audible noise.

Internal circuitry includes charge pump (CP1/CP2) for high-side gate drive, VREG-regulated sink-side bias, ROSC-timed off-time control, and blanking circuitry (1 µs) to suppress false overcurrent detection during switching transients.

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 PCB thermal vias under exposed pad for thermal performance.

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 A3984SLP-T uniquely combines automatic decay mode selection with translator-based simplicity and robust thermal protection - making it optimal for space-constrained, low-software-overhead motion control where step accuracy and acoustic noise matter.

Availability

A3984SLP-T is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pump actuation, and automated retail kiosk printers requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for A3984SLP-T 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 automotive-grade semiconductor solutions.

The A3984 product line delivers integrated stepper drivers with on-chip translators for simplified microstepping implementation in cost-sensitive, space-constrained motion systems - targeting industrial automation, medical devices, and precision instrumentation.

FAQ

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

The A3984SLP-T supports a load supply voltage (VBB) up to 35 V, with absolute maximum rating of 35 V. Operation is specified from 8 V to 35 V. Exceeding 35 V risks permanent damage to the DMOS output stages, even briefly. For reliable 24 V stepper systems, the A3984SLP-T provides sufficient headroom while maintaining low R_DS(ON) efficiency.

How does the A3984SLP-T determine current decay mode during stepping?

The A3984SLP-T compares DAC output levels before and after each STEP pulse. If the new DAC value is higher, it selects Slow decay; if lower, it selects Mixed decay (31.25% fast decay followed by slow decay). This real-time decision occurs independently per full-bridge and is fully automatic - no configuration registers or external control signals are required for decay mode selection in the A3984SLP-T.

Can the A3984SLP-T operate with only one motor supply rail?

Yes. Although VBB1 and VBB2 are separate pins, they may be connected to a common 8–35 V supply. The A3984SLP-T does not require independent rails; using a shared VBB simplifies power design and is validated in Allegro reference layouts. Ensure total current draw (≤4 A combined) and PCB trace width support the summed load.

What is the purpose of the exposed thermal pad on the A3984SLP-T package?

The exposed thermal pad on the A3984SLP-T's 24-pin TSSOP-LP package is electrically connected to internal GND and serves as the primary heat dissipation path. It must be soldered to a PCB copper area with ≥4 thermal vias to an internal ground plane. Without proper thermal pad connection, junction temperature exceeds 150°C at rated current, triggering thermal shutdown and limiting continuous output to <1 A.

Is the A3984SLP-T compatible with 3.3 V microcontrollers?

Yes. The A3984SLP-T logic inputs (STEP, DIR, ENABLE, etc.) accept 3.3 V CMOS levels: V_IN(1) minimum is VDD × 0.7, and VDD operates from 3.0 V to 5.5 V. With VDD = 3.3 V, a 3.3 V MCU output meets the high-level input requirement. Input hysteresis (150–500 mV) further ensures noise immunity in mixed-voltage systems using the A3984SLP-T.