Allegro MicroSystems A3979SLP

Overview

A3979SLP from Allegro MicroSystems is a 28-pin TSSOP microstepping DMOS motor driver IC with integrated translator, designed for bipolar stepper motors in full-, half-, quarter-, and sixteenth-step modes. It delivers ±2.5 A output current at up to 35 V supply, features fixed off-time PWM current regulation with Slow/Fast/Mixed decay control, and includes synchronous rectification, thermal shutdown, UVLO, and crossover-current protection - used in precision motion control systems such as CNC stages and automated optical alignment.

For engineers reviewing the A3979SLP datasheet, A3979SLP pinout, A3979SLP application, or A3979SLP equivalent, this page provides verified technical context, validated pin functions, confirmed microstepping resolution behavior (1/16-step), real-world decay-mode selection logic (PFD-controlled), and alternative part comparisons grounded in Allegro's official documentation and functional specifications.

Technical Context

The A3979SLP implements a dual full-bridge DMOS driver architecture with independent current regulation per phase using external sense resistors (SENSE1/SENSE2) and a DAC-based translator that sequences step currents according to MS1/MS2 inputs. Its fixed off-time PWM timer (t_OFF = 30–46 μs, set by RC1/RC2) supports automatic decay mode selection based on step direction and PFD voltage level (0.21×VDD to 0.6×VDD).

Internal circuitry includes a charge pump (CP1/CP2) for high-side gate drive, VREG-regulated sink-side bias, synchronous rectification (SR-controlled), and fault protection with thermal shutdown (T_JSD = 165°C, hysteresis = 15°C) and UVLO (V_UVLO = 2.45–2.95 V). AGND and PGND must be externally connected at a single star ground point under the exposed thermal pad.

Key Specifications

Pinout & Package

Package: 28-pin TSSOP (LP suffix), low-profile (≤1.20 mm height), lead-free with exposed thermal pad requiring solder connection to PCB ground plane.

Key Features

Applications

Equivalent & Alternatives

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

Compared with A4988TJPTR-T and TMC2209-VQ, the A3979SLP offers superior decay-mode flexibility via PFD control and higher peak current (±2.5 A), making it optimal for applications demanding precise current waveform fidelity without MCU overhead - but requires external sense resistors and discrete timing components.

Availability

A3979SLP is available at Aetrix Electronics and suitable for laser positioning stages, medical infusion pumps, 3D printer extruders, and automated test equipment actuators requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for A3979SLP 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 sensors and power ICs, founded in 1989 and headquartered in Worcester, Massachusetts.

The A3979SLP belongs to Allegro's DMOS microstepping driver product line, engineered specifically for cost-sensitive, high-reliability motion control applications where minimal MCU intervention and robust thermal/electrical protection are essential.

FAQ

What is the maximum microstepping resolution supported by the A3979SLP?

The A3979SLP supports up to 1/16-step microstepping resolution, selected via the MS1 and MS2 logic inputs (both high). This mode delivers 256 steps per full revolution for a standard 1.8° stepper motor, enabling smoother motion and reduced resonance compared to full- or half-step operation. The translator automatically sequences current levels per Table 2 in the datasheet, and the decay mode adapts dynamically to maintain waveform integrity.

How does the PFD pin affect current decay behavior in the A3979SLP?

The PFD pin on the A3979SLP sets the decay mode (Slow, Fast, or Mixed) for each step transition based on its voltage relative to VDD: below 0.21×VDD selects Fast decay, above 0.6×VDD selects Slow decay, and voltages between them enable Mixed decay. This allows fine-tuning of current recirculation to minimize audible noise and distortion - especially critical during direction reversals or acceleration profiles in precision motion systems using the A3979SLP.

Can the A3979SLP operate with a 3.3 V logic supply?

Yes, the A3979SLP supports a logic supply voltage range of 3.0 V to 5.5 V, making it fully compatible with 3.3 V microcontrollers. All logic inputs (STEP, DIR, MS1, MS2, etc.) recognize 0.3×VDD as logic low and 0.7×VDD as logic high - so at 3.3 V, thresholds are ~1.0 V and ~2.3 V respectively. No level-shifting circuitry is required when interfacing the A3979SLP with 3.3 V control systems.

Why must AGND and PGND be connected externally on the A3979SLP?

AGND and PGND must be connected externally - typically at a single star point under the exposed thermal pad - to prevent IR drop errors in current sensing. SENSE1 and SENSE2 reference AGND, while high-current motor return paths flow through PGND. Separating these grounds internally avoids coupling switching noise into the precision current-regulation loop. Failure to tie them externally causes inaccurate ITRIP setting and potential thermal runaway in the A3979SLP.

What is the role of the RC1 and RC2 pins on the A3979SLP?

The RC1 and RC2 pins on the A3979SLP set the fixed off-time (t_OFF) for Bridges 1 and 2 respectively, using external resistor-capacitor networks (RTx/CTx). Typical values (e.g., 56 kΩ + 680 pF) yield t_OFF ≈ 38 μs, which determines minimum step rate and current regulation stability. Independent RC networks allow asymmetric tuning - for example, optimizing Bridge 1 for torque and Bridge 2 for smoothness - a key capability unique to the A3979SLP among Allegro's pin-compatible drivers.