Allegro MicroSystems A3959SLPTR

Overview

A3959SLPTR from Allegro MicroSystems is a DMOS full-bridge PWM motor driver IC designed for bidirectional DC motor control with ±3 A output current and 50 V load supply capability. It implements internal fixed off-time current regulation, synchronous rectification, and selectable slow/fast/mixed decay modes via PFD1/PFD2 inputs. Used in precision speed/direction control of brushed DC motors in industrial actuators and automated equipment.

For engineers reviewing the A3959SLPTR datasheet, A3959SLPTR pinout, A3959SLPTR application, or A3959SLPTR equivalent, key selection criteria include thermal performance on 2-layer PCBs (R_θJA = 40°C/W), TSSOP-28 exposed-pad thermal management, external sense-resistor-based current trip setting (I_TRIP = V_REF/10R_S), and compatibility with 4 MHz internal oscillator timing (ROSC = 51 kΩ).

Technical Context

The A3959SLPTR integrates dual DMOS H-bridge outputs with independent gate drive for source/sink paths, regulated by an internal 4.25 MHz oscillator (±15% tolerance) and fixed 24 µs off-time counter. Current regulation uses a precision 10× reference divider and comparator with ±5 mV offset to set I_TRIP via external V_REF and R_S.

Thermal protection activates at 165°C junction temperature with 15°C hysteresis; undervoltage lockout engages below 3.9 V on V_DD. Synchronous rectification reduces power loss by enabling low-r_DS(on) (270 mΩ typical) recirculation paths during decay, eliminating need for external Schottky diodes.

Key Specifications

Pinout & Package

Package: 28-pin TSSOP (suffix 'LP') with exposed thermal pad (pin 28). All ground pins (7, 8, 28) must be connected together at the exposed pad for optimal thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar full-bridge PWM motor driver applications.

Compared with TB6612FNG and DRV8876N, the A3959SLPTR delivers higher voltage capability (50 V), lower conduction loss (270 mΩ), and deterministic fixed off-time current regulation - making it optimal for thermally constrained industrial actuators where reliability across wide V_BB ranges is critical.

Availability

A3959SLPTR is available at Aetrix Electronics and suitable for industrial actuators, automated valves, medical infusion pumps, robotic joint controllers, and precision DC motor control systems requiring stable component supply across extended production lifecycles.

Supply support for A3959SLPTR 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 sensors and power ICs, specializing in motion control, energy-efficient power conversion, and robust automotive-grade semiconductors.

The A3959SLPTR belongs to Allegro's DMOS full-bridge motor driver product line, engineered for reliable, thermally efficient brushed DC motor control in harsh industrial environments with minimal external components.

FAQ

What is the maximum continuous output current supported by the A3959SLPTR?

The A3959SLPTR supports ±3.0 A continuous output current under specified thermal conditions: 2-layer PCB with 1 in² copper area (R_θJA = 40°C/W), ambient temperature ≤85°C, and proper decoupling. Peak current up to ±6.0 A is allowed for pulses <3 µs. Exceeding these limits risks thermal shutdown activation at 165°C junction temperature.

How does the A3959SLPTR implement current regulation without an external controller?

The A3959SLPTR uses an internal fixed off-time PWM circuit that compares the voltage across an external sense resistor (RS) to a divided reference (V_REF/10). When current reaches I_TRIP = V_REF/10R_S, the source driver turns off for a fixed 24 µs period. This autonomous regulation eliminates need for external microcontroller-based current loop control in basic speed/torque applications.

Can the A3959SLPTR operate with a 3.3 V logic supply?

No - the A3959SLPTR requires a 4.5–5.5 V logic supply (V_DD) per its absolute maximum ratings and electrical characteristics table. Operation below 4.5 V may cause unreliable ENABLE/PHASE input recognition and premature UVLO activation. For 3.3 V systems, level-shifting circuitry or a dedicated 5 V LDO is required before connecting to A3959SLPTR logic inputs.

What is the purpose of the exposed thermal pad on the A3959SLPTR TSSOP package?

The exposed thermal pad (pin 28) on the A3959SLPTR TSSOP package serves as the primary thermal path to the PCB. It must be soldered to a solid copper ground plane with thermal vias to achieve the specified R_θJA = 40°C/W. Leaving it unconnected degrades thermal resistance to ~100°C/W, limiting usable power dissipation to <1.2 W and risking thermal shutdown under load.

Does the A3959SLPTR support regenerative braking?

The A3959SLPTR does not support true regenerative braking (energy return to supply). Its slow-decay braking mode shorts the motor terminals via both sink drivers, dissipating kinetic energy as heat in the MOSFETs and motor winding. Since braking current bypasses the sense resistor, internal current limiting is inactive - designers must ensure peak brake current (≈V_BEMF/R_L) stays within ±6 A peak and 150°C junction limits.