Allegro MicroSystems A3953SLB

Overview

A3953SLB from Allegro MicroSystems is a discontinued 16-pin SOIC full-bridge PWM motor driver IC designed for bidirectional current control of brushed DC and stepper motors. It delivers ±1.3 A continuous output current at up to 50 V load supply, features internal fixed off-time PWM current regulation, thermal shutdown with 8°C hysteresis, and supports fast/slow current-decay modes via MODE input - used in industrial motion control and automotive HVAC actuators.

For engineers reviewing the A3953SLB datasheet, A3953SLB pinout, A3953SLB application, or A3953SLB equivalent, key selection considerations include its SOIC-LB package with fused pins, RC-timed off-time configuration (t_OFF ≈ R_T × C_T), brake-mode override behavior, and discontinuation status requiring legacy design support or migration planning.

Technical Context

The A3953SLB implements a transconductance-based current-sense comparator that compares voltage across an external sense resistor (R_S) against a user-set reference (V_REF) to trigger PWM latch reset. Its fixed off-time one-shot circuit uses an external RC network on the RC pin to determine driver disable duration, with blanking synchronized to PHASE/ENABLE/BRAKE transitions to suppress false trips from clamp diode reverse recovery.

Operation includes three primary functional states: forward/reverse mode (controlled by PHASE and MODE), brake mode (BRAKE = low, overriding ENABLE/PHASE), and sleep mode (ENABLE = MODE = BRAKE = high). Crossover dead time (~0.3–3.0 μs) prevents shoot-through, while internal 1.2–1.6 V clamp diodes handle flyback energy without external components.

Key Specifications

Pinout & Package

Package: 16-pin SOICW (Package LB) with internally fused pins and exposed ground tab (R_θJT = 6°C/W); power tab is at ground potential and requires no electrical isolation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with A3953SLB, the A4973 offers higher current capacity and modern packaging for long-term supply, while the TB6612FNG trades integrated current control for lower system cost and simpler logic interface - making it viable only where external current regulation is already implemented.

Availability

A3953SLB is available at Aetrix Electronics and suitable for industrial valve actuation, automotive HVAC damper control, stepper motor microstepping, and brushed DC servo positioning requiring stable component supply for legacy system maintenance and repair.

Supply support for A3953SLB 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 sensing and power IC solutions, specializing in motion control, current sensing, and motor driver technologies.

The A3953 product line was developed specifically for robust, cost-effective full-bridge motor control in automotive and industrial environments - emphasizing integrated protection, flexible decay-mode selection, and ease of implementation in thermally constrained layouts.

FAQ

Is the A3953SLB still in production?

No, the A3953SLB is a discontinued product. Allegro MicroSystems ceased production effective January 30, 2012. It is not recommended for new designs, and samples are no longer available. Aetrix Electronics maintains limited legacy stock for repair and maintenance of existing systems, with full traceability and documentation support for A3953SLB.

What is the difference between A3953SLB and A3953SB?

The A3953SLB (SOICW package) and A3953SB (16-pin DIP) are electrically identical and share the same pin numbering and functional behavior. The only differences are mechanical: A3953SLB uses a surface-mount SOIC package with internally fused pins and a ground-exposed thermal tab, while A3953SB uses a through-hole DIP with copper heat-sink tabs. Both have R_θJT = 6°C/W but differ in R_θJA (67°C/W vs. 43°C/W).

Can the A3953SLB be used without an external sense resistor?

No. The A3953SLB requires an external current-sense resistor (R_S) connected between SENSE and ground to implement its internal PWM current-control function. The peak trip current I_TRIP is set by V_REF/R_S, and omitting R_S disables current limiting - risking device failure under overload. The SENSE pin has no internal sensing element and must see the voltage drop across R_S.

How does the BRAKE input interact with ENABLE and PHASE on the A3953SLB?

When BRAKE is driven low, it overrides both ENABLE and PHASE inputs: both source drivers turn off and both sink drivers turn on, forcing motor terminals to ground - enabling dynamic braking regardless of other control signals. This priority behavior is hardwired and cannot be disabled. When BRAKE is high, normal PHASE/ENABLE/MODE operation resumes.

What thermal management is required for reliable A3953SLB operation at ±1.3 A?

At ±1.3 A continuous, the A3953SLB requires PCB copper area connected to its exposed ground tab to maintain junction temperature below 125°C. With R_θJT = 6°C/W, a 2-layer board with ≥0.3 in² (≈2 cm²) of 2-oz copper per side achieves R_θJA ≈ 67°C/W. For ambient temperatures above 60°C or duty cycles >50%, additional copper area (6–18 cm²) or forced air cooling is recommended to prevent thermal shutdown activation.