Allegro MicroSystems A3973SLB

Overview

A3973SLB from Allegro MicroSystems is a dual DMOS full-bridge PWM motor driver designed for bipolar microstepping stepper motors, supporting ±1 A continuous output current at up to 35 V supply, with two 6-bit linear DACs for precise torque control and programmable mixed/fast/slow current-decay modes in industrial motion control systems.

For engineers reviewing the A3973SLB datasheet, A3973SLB pinout, A3973SLB application, or A3973SLB equivalent, this page provides verified electrical parameters, SOICW package details, synchronous rectification behavior, thermal shutdown thresholds, and serial interface timing constraints critical for motor driver layout and firmware integration.

Technical Context

The A3973SLB integrates two independent H-bridges with fixed-off-time PWM current regulation, each controlled by a dedicated 6-bit DAC and selectable decay mode (mixed/fast/slow) via serial configuration. Its internal 4 MHz oscillator or external clock input drives programmable blank time (4–12/f_OSC) and off-time (1.75–63.75 μs).

Synchronous rectification is configurable across four modes (active/passive/disabled/low-side-only) using two serial bits, enabling optimized power dissipation during current decay. The device uses internal 2 V reference (±10 mV offset) or external reference (≤3 V), with gain scaling of ×4 or ×8 selected by D18 to set I_TRIP = V_DAC/(Range × R_S).

Key Specifications

Pinout & Package

The A3973SLB is housed in a 24-pin SOICW (Small Outline Integrated Circuit Wide) package with internally fused leads at pins 6, 7, 18, and 19 for enhanced thermal dissipation. Power tabs are grounded and require no electrical isolation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TB6600HG and DRV8825, the A3973SLB uniquely delivers dual-bridge coordination, on-chip 6-bit DACs, and serial programmability in a single SOICW package-enabling synchronized microstepping across two axes without additional timing logic or external DACs.

Availability

A3973SLB is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory analyzers, and 3D printer extruder control requiring stable component supply and long-term production continuity.

Supply support for A3973SLB 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, headquartered in Worcester, Massachusetts, with global manufacturing and support infrastructure.

The A3973SLB belongs to Allegro's motor driver product line engineered specifically for precision bipolar stepper motor control in industrial automation, medical equipment, and instrumentation-emphasizing integrated current regulation, thermal robustness, and programmable decay timing.

FAQ

What is the maximum continuous output current supported by the A3973SLB?

The A3973SLB supports ±1.0 A continuous output current per bridge at ambient temperatures up to +85°C with adequate PCB copper area. This rating assumes use of the LB package's fused leads and proper thermal layout per Allegro's recommended footprint. Exceeding this current without enhanced heatsinking risks triggering thermal shutdown at 165°C junction temperature.

Does the A3973SLB require external Schottky diodes for clamp protection?

No, the A3973SLB does not require external Schottky diodes due to its integrated synchronous rectification circuitry. When configured in active or low-side-only mode, the device uses its own low-R_DS(on) DMOS transistors to recirculate current during decay, eliminating body-diode conduction losses. External diodes are only needed if synchronous rectification is explicitly disabled via serial control bits.

How is current level programmed on the A3973SLB?

Current level on the A3973SLB is programmed via two independent 6-bit linear DACs accessible through its 3-wire serial interface. Each DAC sets the reference voltage for one H-bridge using the formula I_TRIP = V_DAC/(Range × R_S), where Range is ×4 or ×8 selected by D18, and R_S is the external sense resistor value. DAC codes 1–63 yield 1.56% incremental steps from minimum to full-scale current.

What are the key timing requirements for the A3973SLB serial interface?

The A3973SLB serial interface requires minimum 15 ns data setup time before CLOCK rising edge, 10 ns data hold time after CLOCK rising edge, and 150 ns minimum STROBE pulse width. STROBE must be held high except during write cycles, and the 19-bit word (MSB first) is latched on the falling edge of STROBE. These constraints ensure reliable register updates without corruption during high-speed MCU communication.

Can the A3973SLB operate with a 3.3 V logic supply?

Yes, the A3973SLB accepts 3.3 V or 5 V logic supply voltages on VDD, with input thresholds defined as VIN(1) ≥ 2.0 V and VIN(0) ≤ 0.8 V. Its logic inputs are fully compatible with 3.3 V CMOS levels, enabling direct connection to ARM Cortex-M or ESP32 microcontrollers without level shifters. The internal UVLO circuit activates at 3.9 V, ensuring stable operation across the full 3.3–5.5 V VDD range.