Allegro MicroSystems A3972SB

Overview

A3972SB from Allegro MicroSystems is a dual DMOS full-bridge PWM motor driver IC designed for bipolar microstepping stepper motor control, delivering ±1.5 A continuous output current at up to 50 V supply voltage, with internal 4 MHz oscillator, 6-bit linear DACs for torque resolution in 1.56% increments, and programmable mixed/fast/slow current-decay modes - used in precision motion control systems such as CNC stages and automated optical positioning.

For engineers reviewing the A3972SB datasheet, A3972SB pinout, A3972SB application, or A3972SB equivalent, key selection criteria include its 24-pin DIP package with fused power tabs, synchronous rectification eliminating external clamp diodes, serial 3-wire interface (clock/data/strobe), thermal shutdown at 165°C, and compatibility with both 3.3 V and 5 V logic inputs.

Technical Context

The A3972SB integrates two independent H-bridge drivers, each controlled by a dedicated 6-bit linear DAC and configurable PWM timer with fixed off-time architecture. Its internal oscillator operates at 4 MHz (±25% typical) and supports external clock input with selectable dividers (×1/2/4).

Current regulation uses either internal 2.0 V reference (±30 mV offset) or external reference up to 3 V, scaled by programmable gain (×4 or ×8) to set ITRIP = VDAC/(Range × RS). Synchronous rectification is configurable via two serial bits into Active, Passive, Disabled, or Low-Side-Only modes to optimize recirculation path efficiency.

Key Specifications

Pinout & Package

Package: 24-pin plastic DIP with two batwing power tabs (pins 6, 7, 18, 19 internally fused); power tabs are at ground potential and require no electrical isolation. Lead finish: 100% matte tin, Pb-free.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TB6600HG and DRV8825, the A3972SB uniquely provides two fully independent 6-bit DAC-controlled bridges with per-bridge decay mode selection, 4 MHz timing resolution, and synchronous rectification - making it the only option supporting simultaneous, differentially tuned microstepping on two axes without external logic.

Availability

A3972SB is available at Aetrix Electronics and suitable for industrial CNC positioning, automated optical alignment, medical infusion pumps, lab automation robotics, and precision motion control systems requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for A3972SB 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, founded in 1989 and headquartered in Worcester, Massachusetts.

The A3972SB belongs to Allegro's legacy motor driver product line focused on integrated, programmable stepper and BLDC solutions for industrial automation, medical equipment, and precision instrumentation - emphasizing thermal robustness, analog accuracy, and flexible digital control.

FAQ

What is the maximum operating voltage for the A3972SB?

The A3972SB supports a load supply voltage (VBB) range of 15 V to 50 V. This allows direct integration into common industrial DC bus systems such as 24 V and 48 V rails. Exceeding 50 V risks permanent damage to the DMOS output stages, and operation below 15 V may prevent proper current regulation due to insufficient headroom for the internal charge pump and VREG circuitry. The A3972SB datasheet specifies absolute maximum VBB as 50 V with no derating required within this range.

Does the A3972SB require external Schottky diodes for flyback protection?

No, the A3972SB does not require external Schottky diodes in most applications due to its integrated synchronous rectification feature. When enabled, the device actively turns on appropriate low-RDS(on) DMOS transistors during current decay to bypass body diode conduction, reducing power loss and eliminating the need for four external clamp diodes per bridge. External diodes are only necessary if synchronous rectification is disabled via serial control bits D14/D15.

How is microstepping resolution achieved in the A3972SB?

The A3972SB achieves microstepping resolution through two independent 6-bit linear DACs - one per H-bridge - that set reference currents in 64 discrete steps (1.56% increments of full-scale). These DAC outputs feed current comparators that regulate phase current via PWM. Combined with programmable decay modes (mixed/fast/slow), the A3972SB supports full-step through 1/16-step operation with smooth torque transitions and minimal resonance.

Can the A3972SB drive two independent stepper motors simultaneously?

Yes, the A3972SB integrates two fully independent DMOS full-bridge drivers (Bridge 1 and Bridge 2), each with dedicated DACs, sense inputs, and decay-mode controls. This allows simultaneous, asymmetric microstepping of two bipolar stepper motors - for example, running one motor at 1/8-step with mixed decay while the other operates at full-step with slow decay - all managed via a single serial interface.

What thermal protection features does the A3972SB include?

The A3972SB includes junction-temperature-based thermal shutdown triggered at 165°C (typical) with 15°C hysteresis, ensuring automatic recovery once temperature falls below 150°C. It also monitors VREG and VCP supply voltages, disabling outputs if either drops below safe thresholds. Unlike many competitors, the A3972SB requires no special power-up sequencing and incorporates crossover-current protection to prevent shoot-through during switching transitions.