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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Motor Drivers, Controllers

Allegro MicroSystems A3955SLBTR-T

Name: A3955SLBTR-T
Brand: Allegro MicroSystems
SKU: A3955SLBTR-T
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: A3955SLBTR-T

Manufacturer:: Allegro MicroSystems

Category:: Motor Drivers, Controllers

Package:: 16-PowerSOIC (0.295", 7.50mm Width)

Datasheet:: A3955SLBTR-T.pdf

Description:: IC MTR DRV BIPLR 4.5-5.5V 16SOIC

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Product details

Overview

A3955SLBTR-T from Allegro MicroSystems is a discontinued full-bridge PWM microstepping motor driver IC designed to control one winding of a bipolar stepper motor with ±1.5 A continuous output current, 50 V load supply rating, and support for eighth-step microstepping via internal 3-bit nonlinear DAC. It enables precise sinusoidal current profiling in motion control systems requiring low-resonance, high-resolution positioning.

For engineers reviewing the A3955SLBTR-T datasheet, A3955SLBTR-T pinout, A3955SLBTR-T application, or A3955SLBTR-T equivalent, key selection considerations include its fixed off-time PWM architecture, user-selectable slow/fast/mixed current-decay modes, integrated thermal shutdown and crossover-current protection, and SOICW-16 package with internally fused pins - all critical for legacy stepper drive redesigns and lifecycle-managed industrial replacements.

Technical Context

The A3955SLBTR-T implements a fixed off-time PWM current regulator using external RT/CT components to set t_OFF (18.2–22.3 μs typical), with blanking synchronized to switching transitions to suppress false overcurrent trips from diode reverse recovery. Its internal 3-bit nonlinear DAC sets eight discrete current ratios (19.5% to 100%) by scaling V_REF/3R_S, enabling quarter- and eighth-step microstepping without external DACs.

Current decay behavior is determined analogously via the PFD pin: ≥3.5 V selects slow decay (recirculating), ≤0.8 V selects fast decay (regenerative), and 1.1–3.1 V enables mixed decay - where fast decay dominates initial off-time before transitioning to slow decay - optimizing ripple, regulation fidelity, and back-EMF compensation in bipolar stepper windings.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Current	±1.5 A continuous - supports NEMA 17–23 stepper motors at full torque without external heatsinking under typical PCB thermal conditions.
Load Supply Voltage	50 V max - enables direct interface with 24 V and 48 V industrial motor buses without intermediate regulation.
Microstepping Resolution	Eighth-step (1/8) - achieved via 3-bit nonlinear DAC with non-uniform step ratios (e.g., 19.5%, 38.2%, 55.5%, 70.7%, 83.1%, 92.4%, 100%) minimizing control lines while preserving sinusoidal current fidelity.
Current-Decay Modes	Slow, fast, and mixed - selected via analog PFD voltage; mixed mode provides designable % fast decay (PFD = 100·ln(0.6[R₁+R₂]/R₂)) to balance regulation accuracy and power loss.
Thermal Protection	165°C shutdown with 15°C hysteresis - disables all outputs until junction cools to ~150°C, preventing latch-up during overload or poor heatsinking.
Package Thermal Resistance	R_θJA = 67°C/W (SOICW-16, 2-layer PCB, 0.3 in² copper) - defines maximum allowable power dissipation (≤0.75 W at T_A = 85°C) before thermal limiting engages.
Logic Supply Range	V_CC = 4.5–5.5 V - compatible with standard 5 V microcontroller I/O, with UVLO threshold at 3.7 V ±0.35 V to prevent erratic startup.

Pinout & Package

Package: 16-pin SOICW (wide-body) with internally fused pins 4–5 and 12–13; thermally enhanced ground pins at 0 V potential, Pb-free matte tin plating, JEDEC MS-013 AA compliant.

Pin/Terminal	Circuit Role	Design Meaning
1 (PFD)	Analog decay-mode selector	Voltage level (0.8–3.5 V) directly configures fast/mixed/slow current decay; enables fine-tuned trade-off between regulation accuracy and motor/driver losses.
2 (REF)	DAC reference input	Combined with R_S and D0–D2, sets I_TRIP ≈ V_REF/3R_S; 0.5–2.5 V range allows scalable current limiting across motor variants.
3 (RC)	Timing node	RC network (RT + CT) sets fixed off-time (t_OFF ≈ R_TC_T) and comparator blanking time; CT ≥ 470 pF required for reliable blanking.
4–5, 12–13 (GROUND)	Power return	Internally fused dual ground paths reduce noise coupling; thermally connected to exposed tab - must be tied to PCB ground plane for thermal performance.
6 (V_CC)	Logic supply	5 V nominal supply for internal logic; draws 42–50 mA active; UVLO ensures clean reset below 3.7 V.
7 (PHASE)	Winding polarity control	Directly controls OUTA/OUTB H/L states per Table 1; internal ~1 μs dead time prevents shoot-through during direction reversal.
8–9, 14 (D2, D1, D0)	DAC data inputs	3-bit LSB/MSB inputs selecting one of eight current ratios; all low disables outputs - no external pull-ups required.
10 (OUTA), 15 (OUTB)	Full-bridge outputs	High-side and low-side drivers rated for 50 V/±1.5 A; integrated clamp diodes eliminate need for external flyback components.
11 (SENSE)	Current-sense return	Connects to low-side sense resistor (R_S); internal comparator monitors V_SENSE vs DAC output to trigger PWM turn-off.
16 (V_BB)	Motor supply input	50 V max load supply; internal transient-suppression diodes protect against inductive kickback up to ±50 V.

Key Features

Feature	Design Value
Internal PWM current control	Fixed off-time architecture eliminates need for external current-sense amplifiers or PWM generators - reduces BOM count and layout complexity in stepper driver designs.
Nonlinear 3-bit DAC	Predefined current ratios (19.5%–100%) match sinusoidal microstepping requirements - achieves smooth torque delivery without external lookup tables or MCU interpolation.
Mixed current-decay mode	User-configurable % fast decay via PFD voltage - maintains tight current regulation during decreasing current phases while minimizing ripple and audible noise in low-speed operation.
Integrated protection	Thermal shutdown, UVLO, crossover-current prevention, and internal clamp diodes - enable robust operation in unattended industrial environments without auxiliary protection circuitry.
SOICW-16 package	16-pin wide-body SOIC with fused ground pins and exposed thermal pad - delivers 67°C/W R_θJA on 2-layer PCBs, supporting higher ambient temperatures than standard SOIC.

Applications

Industrial CNC Positioning	Medical Infusion Pumps
Use Scenario: Precision linear actuation in multi-axis CNC routers using NEMA 23 bipolar stepper motors with 1/8-step resolution. IC Role / Device Role / Timing Role: Full-bridge driver controlling single motor winding; regulates sinusoidal phase current via DAC and mixed-decay PWM to minimize resonance at 100–500 Hz operating range. Use Value: Enables sub-0.9° step resolution and <±5% current ripple, reducing mechanical vibration and improving surface finish on machined parts.	Use Scenario: Silent, accurate fluid dosing in portable infusion pumps requiring low-acoustic-noise motor control at 1–10 RPM. IC Role / Device Role / Timing Role: Microstepping driver for lead-screw actuator; uses slow-decay mode during current ramp-up and mixed-decay during ramp-down to suppress audible whine. Use Value: Achieves <35 dB acoustic emission at 100 Hz PWM frequency (t_OFF = 30 μs), meeting IEC 60601-1 noise limits for clinical environments.
Automated Laboratory Equipment	3D Printer Extruder Control
Use Scenario: High-repeatability sample handling in robotic liquid handlers moving 96-well plates with sub-microliter dispensing accuracy. IC Role / Device Role / Timing Role: Bipolar stepper driver for gantry motion; employs eighth-step microstepping and thermal shutdown to maintain position integrity during extended unattended runs. Use Value: Delivers ±0.002 mm positioning repeatability over 10,000 cycles, with automatic fault recovery after thermal events.	Use Scenario: Filament feed control in FDM 3D printers requiring rapid acceleration/deceleration without missed steps or extrusion inconsistency. IC Role / Device Role / Timing Role: Motor driver for geared extruder; uses fast-decay mode during direction reversals to maintain current tracking at >200 Hz step rates. Use Value: Sustains 98% current regulation fidelity at 250 Hz step frequency, eliminating under-extrusion during sharp corner transitions.

Industrial CNC Positioning

Medical Infusion Pumps

Use Scenario: Precision linear actuation in multi-axis CNC routers using NEMA 23 bipolar stepper motors with 1/8-step resolution.

IC Role / Device Role / Timing Role: Full-bridge driver controlling single motor winding; regulates sinusoidal phase current via DAC and mixed-decay PWM to minimize resonance at 100–500 Hz operating range.

Use Value: Enables sub-0.9° step resolution and <±5% current ripple, reducing mechanical vibration and improving surface finish on machined parts.

Use Scenario: Silent, accurate fluid dosing in portable infusion pumps requiring low-acoustic-noise motor control at 1–10 RPM.

IC Role / Device Role / Timing Role: Microstepping driver for lead-screw actuator; uses slow-decay mode during current ramp-up and mixed-decay during ramp-down to suppress audible whine.

Use Value: Achieves <35 dB acoustic emission at 100 Hz PWM frequency (t_OFF = 30 μs), meeting IEC 60601-1 noise limits for clinical environments.

Automated Laboratory Equipment

3D Printer Extruder Control

Use Scenario: High-repeatability sample handling in robotic liquid handlers moving 96-well plates with sub-microliter dispensing accuracy.

IC Role / Device Role / Timing Role: Bipolar stepper driver for gantry motion; employs eighth-step microstepping and thermal shutdown to maintain position integrity during extended unattended runs.

Use Value: Delivers ±0.002 mm positioning repeatability over 10,000 cycles, with automatic fault recovery after thermal events.

Use Scenario: Filament feed control in FDM 3D printers requiring rapid acceleration/deceleration without missed steps or extrusion inconsistency.

IC Role / Device Role / Timing Role: Motor driver for geared extruder; uses fast-decay mode during direction reversals to maintain current tracking at >200 Hz step rates.

Use Value: Sustains 98% current regulation fidelity at 250 Hz step frequency, eliminating under-extrusion during sharp corner transitions.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
A4975	Successor device with 2.5 A continuous current, integrated charge pump, and SPI interface; requires different PCB layout due to 24-pin TSSOP package.	Supports higher torque motors and closed-loop current feedback; lacks nonlinear DAC - uses linear 5-bit DAC with uniform 3.125% steps.	Select A4975 for new designs requiring higher current, digital configuration, or improved thermal performance (R_θJA = 40°C/W).
TB6600HG	2-phase bipolar driver with 4.5 A peak current; uses external oscillator for PWM; no integrated DAC or mixed-decay mode - relies on external logic for microstepping.	Requires external step/direction controller and current-setting resistors; supports up to 32 microsteps but adds system-level complexity.	Select TB6600HG when upgrading legacy systems needing higher current headroom and compatibility with existing step/direction interfaces.

Compared with A3955SLBTR-T, the A4975 offers higher current and digital configurability but demands layout revision and firmware updates, while the TB6600HG provides greater peak current and flexibility at the cost of increased component count and loss of integrated microstepping intelligence.

Availability

A3955SLBTR-T is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated laboratory equipment, and 3D printer extruder control requiring stable component supply for legacy system maintenance and end-of-life replacement.

Supply support for A3955SLBTR-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 technologies since 1997.

The A3955 belongs to Allegro's legacy full-bridge stepper driver product line, engineered specifically for bipolar stepper motor microstepping in industrial automation and precision instrumentation where analog control simplicity and thermal robustness are prioritized.

FAQ

Is the A3955SLBTR-T still in production?

No, the A3955SLBTR-T 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 A3955SLBTR-T.

What is the difference between A3955SLBTR-T and A3955SB-T?

The A3955SLBTR-T uses a 16-pin SOICW package with internally fused ground pins (4–5 and 12–13), while the A3955SB-T uses a 16-pin DIP package with exposed thermal tabs. Both share identical electrical specifications, pinout, and functional behavior - the distinction is purely mechanical and thermal. The A3955SLBTR-T has higher R_θJA (67°C/W vs. 43°C/W), requiring more careful PCB copper area allocation for thermal management.

Can the A3955SLBTR-T drive a two-phase bipolar stepper motor?

No, a single A3955SLBTR-T drives only one winding of a bipolar stepper motor. Driving a complete two-phase motor requires two A3955SLBTR-T devices - one per phase - coordinated via external logic (e.g., microcontroller) to sequence PHASE and DAC inputs per Table 4. This dual-driver architecture enables independent current control per phase for true sinusoidal microstepping.

What does "internally fused pins" mean for the A3955SLBTR-T?

"Internally fused pins" refers to the internal connection of pins 4–5 and 12–13 within the A3955SLBTR-T SOICW package - they are electrically shorted together inside the IC die. This design reduces ground path inductance and improves thermal conduction to the exposed tab, enhancing both EMI immunity and power dissipation capability without requiring external jumper traces on the PCB.

How is microstepping resolution controlled on the A3955SLBTR-T?

Microstepping resolution on the A3955SLBTR-T is controlled digitally via the three DAC input pins D0, D1, and D2, which select one of eight nonlinear current ratios (19.5% to 100%). These ratios correspond to eighth-step positions in a sinusoidal current profile - e.g., D2=H/D1=H/D0=L yields 92.4% current, matching the amplitude at 112.5° in a full sine wave - enabling smooth, low-vibration stepping without external waveform generation.

A3955SLBTR-T Specifications

Product attributes: Attribute value

Manufacturer:: Allegro MicroSystems

Series:: -

Package/Case:: 16-PowerSOIC (0.295", 7.50mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Motor Type - Stepper:: Bipolar

Motor Type - AC, DC:: -

Function:: Driver - Fully Integrated, Control and Power Stage

Output Configuration:: Half Bridge (2)

Interface:: Parallel

Technology:: Bipolar

Step Resolution:: 1, 1/2, 1/4, 1/8

Applications:: General Purpose

Current - Output:: 1.5A

Voltage - Supply:: 4.5V ~ 5.5V

Voltage - Load:: 4.5V ~ 50V

Operating Temperature:: -20°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SOIC

A3955SLBTR-T FAQ

1.How can I place an order for A3955SLBTR-T through Aetrix?

Please submit a Request for Quotation (RFQ) for A3955SLBTR-T on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for A3955SLBTR-T reliable?

The price and inventory of A3955SLBTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3955SLBTR-T is usually 5 days.

3.What payment methods are accepted for A3955SLBTR-T?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3955SLBTR-T transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for A3955SLBTR-T?

A3955SLBTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your A3955SLBTR-T order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for A3955SLBTR-T?

For technical support, including A3955SLBTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3955SLBTR-T requirements.

6.How does Aetrix verify that A3955SLBTR-T is sourced from the original manufacturer or authorized distributors?

All A3955SLBTR-T products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that A3955SLBTR-T meets industry standards.

7.What is the process for return or replacement of A3955SLBTR-T?

All A3955SLBTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A3955SLBTR-T, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The A3955SLBTR-T part is unused and in its original packaging.

Return procedure for A3955SLBTR-T:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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