Allegro MicroSystems A3958SLB-T

Overview

A3958SLB-T from Allegro MicroSystems is a DMOS full-bridge PWM motor driver IC designed for bidirectional DC motor control with programmable current regulation. It delivers ±2 A continuous output current at up to 50 V supply voltage, supports serial-programmable slow/fast/mixed current-decay modes, and integrates synchronous rectification to reduce power dissipation in H-bridge motor drive applications such as industrial actuators and precision positioning systems.

For engineers reviewing the A3958SLB-T datasheet, A3958SLB-T pinout, A3958SLB-T application, or A3958SLB-T equivalent, key selection criteria include its 24-pin SOICW package with internally fused pins, fixed-off-time PWM timing architecture, 270 mΩ typical r_DS(on), thermal shutdown at 165°C, and 3-wire serial interface (CLOCK/DATA/STROBE) for real-time decay-mode and blank-time configuration.

Technical Context

The A3958SLB-T implements a fixed-off-time PWM current-control architecture with programmable blank time (4–24/f_OSC) and off-time (1.75–63.75 μs at 4 MHz), enabling precise motor winding current regulation via external sense resistor and VREF. Its serial interface configures decay mode (slow/mixed/fast), synchronous rectification (active/passive/disabled), and sleep mode-directly affecting recirculation path efficiency and braking behavior.

Internally, it integrates charge pump (CP/CP1/CP2) for high-side gate drive, VREG regulator for sink-side drivers, and fault protection including UVLO (4.2 V enable threshold), thermal shutdown (165°C, 15°C hysteresis), and crossover-current protection. All power pins operate at ground potential, eliminating need for electrical isolation in PCB layout.

Key Specifications

Pinout & Package

Package: 24-pin SOICW (suffix 'LB') with internally fused pins 6/7 and 18/19; lead-free, 100% matte tin leadframe; R_θJA = 77°C/W (minimal copper).

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 A3958SLB-T uniquely combines ±2 A continuous rating, serial-programmable decay modes, integrated charge pump for 50 V operation, and ground-referenced power architecture - making it optimal for thermally constrained, medium-power industrial motion systems requiring field-configurable motor dynamics.

Availability

A3958SLB-T is available at Aetrix Electronics and suitable for industrial actuators, medical pump drives, automated test equipment, and lab instrument positioning requiring stable component supply and long-term lifecycle support.

Supply support for A3958SLB-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 IC solutions, specializing in motion control, current sensing, and motor driver technology since 1989.

The A3958 product line was developed specifically for robust, programmable DC motor control in industrial and medical applications where thermal resilience, current accuracy, and flexible decay-mode tuning are critical system requirements.

FAQ

What is the maximum continuous output current supported by the A3958SLB-T?

The A3958SLB-T supports ±2 A continuous output current under specified thermal conditions (TA = 25°C, adequate PCB copper). This rating assumes proper heatsinking and adherence to the 77°C/W junction-to-ambient thermal resistance for the SOICW package. Exceeding this current without derating risks thermal shutdown activation at 165°C junction temperature.

Does the A3958SLB-T require an external oscillator, or does it include an internal clock source?

The A3958SLB-T requires an external square-wave oscillator signal applied to the OSC pin (pin 5 in SOICW), with frequency ranging from 2.9 to 6.1 MHz. It does not contain an internal oscillator; the external clock directly sets PWM timing resolution, blank time, and off-time intervals via the formula toff = (8[1 + N]/f_OSC) − 1/f_OSC.

How does synchronous rectification function in the A3958SLB-T, and how is it configured?

In the A3958SLB-T, synchronous rectification replaces lossy body-diode conduction during current decay with low-r_DS(on) DMOS paths. It is configured via serial port bits D11 (mode: active/passive) and D12 (enable/disable), allowing optimization for torque ripple, braking efficiency, or reverse-current suppression - all without changing hardware.

Can the A3958SLB-T be used with a 3.3 V microcontroller for its serial interface and logic inputs?

No - the A3958SLB-T logic supply (VDD) requires 4.5–5.5 V, and its digital inputs (PHASE, ENABLE, DATA, CLOCK, STROBE, MODE, RANGE, OSC) are TTL/CMOS-compatible with VDD = 5 V. Driving inputs from a 3.3 V MCU requires level-shifting circuitry to meet the VIN(1) ≥ 2.0 V and VIN(0) ≤ 0.8 V thresholds under all operating conditions.

What protection features are integrated into the A3958SLB-T, and how do they respond to fault conditions?

The A3958SLB-T integrates UVLO (disables drivers below 4.2 V VDD), thermal shutdown (turns off all outputs at 165°C, re-enables after 15°C hysteresis), and crossover-current protection (prevents shoot-through during switching transitions). All faults disable outputs until cleared - no latch-up occurs, and serial register contents persist across UVLO events.