Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

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

Allegro MicroSystems A3955SLBTR

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

Compare

Part No.:: A3955SLBTR

Manufacturer:: Allegro MicroSystems

Category:: Motor Drivers, Controllers

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

Datasheet:: A3955SLBTR.pdf

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

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:4,082

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

A3955SLBTR 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 its internal 3-bit nonlinear DAC. It operates in slow, fast, or mixed current-decay modes to optimize torque smoothness and low-speed resonance suppression in precision motion systems.

For engineers reviewing the A3955SLBTR datasheet, A3955SLBTR pinout, A3955SLBTR application, or A3955SLBTR equivalent, this page delivers verified technical context, validated pin functions, confirmed microstepping step sequencing, thermal shutdown behavior, and documented alternative options for legacy design continuity and migration planning.

Technical Context

The A3955SLBTR implements fixed-off-time PWM current regulation using an external RT/CT network (e.g., RT = 43 kΩ, CT = 470 pF yields t_OFF ≈ 20.2 μs), with comparator blanking synchronized to RC terminal voltage transitions to suppress false overcurrent trips from diode reverse recovery. Its nonlinear DAC sets eight discrete current ratios (19.5%–100%) by scaling V_REF/3R_S, enabling precise sinusoidal current profiling without external DACs.

Current decay mode is selected analogically via the PFD input: ≥3.5 V enables slow decay (recirculation through sink path), ≤0.8 V enables fast decay (regenerative flyback), and 1.1–3.1 V enables mixed decay-where fast decay dominates the initial portion of t_OFF, then switches to slow decay-balancing regulation fidelity and ripple-induced losses.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Current	±1.5 A continuous - supports bipolar stepper windings up to 1.5 A without external heatsinking under specified thermal conditions.
Load Supply Voltage	50 V max - enables direct drive of industrial stepper motors requiring high-voltage operation (e.g., 24–48 V systems).
Microstepping Resolution	Eighth-step (1/8-step) - achieves 8 discrete current levels per full step via 3-bit nonlinear DAC, reducing low-speed vibration and resonance.
PWM Off-Time Range	18.2–22.3 μs (typ. 20.2 μs with RT=43 kΩ, CT=470 pF) - user-adjustable via RC network to balance EMI, switching loss, and current regulation accuracy.
Current-Decay Modes	Slow, fast, and mixed - selectable via analog PFD voltage to adapt decay dynamics to back-EMF conditions and maintain sinusoidal current fidelity.
Junction Temp. Limit	165°C thermal shutdown with 15°C hysteresis - protects against sustained overload or inadequate PCB copper area (e.g., R_θJA = 67°C/W for LB package).
Logic Supply Range	4.5–5.5 V - compatible with standard 5 V microcontroller I/O without level shifting; UVLO threshold at 3.7 V typical.

Pinout & Package

Package: 16-pin SOICW (suffix 'LB') with internally fused pins 4–5 and 12–13; thermally enhanced ground pins at 0 V potential; lead-free matte tin plating.

Pin/Terminal	Circuit Role	Design Meaning
1 (PFD)	Analog current-decay mode selector	Voltage input (0.8–3.5 V range) that configures fast/mixed/slow decay - critical for maintaining current waveform integrity during direction reversal or deceleration.
2 (REF)	Reference voltage input	Sets peak current threshold with RS and DAC bits; V_REF = 0.5–2.5 V range defines I_TRIP ≈ (SRCR × V_REF) / 3R_S.
3 (RC)	RC timing network node	Connects external RT and CT to set PWM off-time and comparator blanking duration - blanking prevents false trips during PHASE transitions or power-up.
4–5, 12–13 (GROUND)	Common return path	Internally fused ground pins provide low-inductance return for logic (V_CC) and load (V_BB) supplies; must be tied to PCB ground plane for thermal and noise performance.
6 (V_CC)	Logic supply input	Supplies internal logic and DAC; requires stable 4.5–5.5 V; draws 42–50 mA when active.
7 (PHASE)	Winding polarity control	Digital input determining current direction in motor winding (H = OUTA high/OUTB low; L = OUTA low/OUTB high); includes ~1 μs internal dead time to prevent shoot-through.
8–9, 14 (D2, D1, D0)	DAC data inputs	3-bit MSB-to-LSB control lines selecting one of eight current ratios (0% to 100%); all low disables outputs.
10 (OUTA), 15 (OUTB)	Full-bridge output terminals	High-current H-bridge outputs driving one stepper winding; rated for 50 V and ±1.5 A; include integrated clamp diodes.
11 (SENSE)	Current-sense return	Connects to low-side sense resistor (R_S); voltage at this pin compared to DAC output to trigger PWM turn-off at I_TRIP.
16 (V_BB)	Motor supply input	High-voltage supply for bridge outputs; accepts 5–50 V; internal transient-suppression diodes protect against inductive kickback.

Key Features

Feature	Design Value
Internal PWM current control	Fixed-off-time architecture eliminates need for external current-sense amplifier or PWM generator - reduces BOM count and layout complexity.
Nonlinear 3-bit DAC	Delivers non-uniform current steps (19.5%, 38.2%, 55.5%, 70.7%, 83.1%, 92.4%, 100%) matching sinusoidal microstepping requirements - minimizes torque ripple vs. linear DAC.
Mixed current-decay mode	Enables dynamic decay profile: fast decay initiates rapid current reduction, then switches to slow decay to limit ripple - preserves average current accuracy while avoiding back-EMF-induced current overshoot.
Integrated protection	Thermal shutdown (165°C), UVLO (3.7 V), crossover-current prevention, and internal clamp diodes eliminate need for external protection components in most stepper drive applications.
RC-based blanking	Comparator blanking time derived from same RC network used for off-time setting - ensures consistent noise immunity across operating conditions without additional timing components.

Applications

Industrial CNC Positioning	Medical Infusion Pumps
Use Scenario: Precision open-loop positioning of X/Y stages in benchtop CNC mills using 1.8° bipolar stepper motors. IC Role / Device Role / Timing Role: Full-bridge driver controlling single motor phase with eighth-step microstepping to achieve 0.225° effective step resolution and suppress 100–200 Hz mechanical resonance. Use Value: Nonlinear DAC and mixed-decay mode maintain sinusoidal current waveforms across speed ranges, reducing audible noise and positional error caused by torque variation.	Use Scenario: Low-vibration, repeatable syringe actuation in portable infusion pumps delivering precise drug dosages over extended periods. IC Role / Device Role / Timing Role: Motor winding controller implementing quarter- and eighth-step microstepping to minimize step-induced pulsation and ensure smooth fluid displacement. Use Value: Internal thermal shutdown and UVLO prevent unintended motor motion during brown-out or overheating, supporting Class II medical device safety requirements.
Lab Automation Robotics	3D Printer Extruder Control
Use Scenario: Multi-axis robotic arm end-effector movement in automated sample handling systems requiring silent, jitter-free motion between discrete positions. IC Role / Device Role / Timing Role: One of two A3955SLBTR drivers per motor (dual-winding control) executing microstepping sequences per Table 4 to generate coordinated sinusoidal phase currents. Use Value: Slow-decay mode during current ramp-up and mixed-decay during ramp-down preserve current waveform fidelity, eliminating position lag during acceleration/deceleration profiles.	Use Scenario: High-resolution filament feed control in FDM 3D printers where extruder stepper motor must respond rapidly to G-code velocity commands without skipping steps. IC Role / Device Role / Timing Role: Winding driver regulating current to ±1.5 A at 24 V supply, using fast-decay mode during rapid direction reversals to maintain closed-loop-like current tracking. Use Value: 50 V rating and integrated clamp diodes tolerate inductive kickback from fast PWM transitions, improving reliability in compact, thermally constrained printer enclosures.

Industrial CNC Positioning

Medical Infusion Pumps

Use Scenario: Precision open-loop positioning of X/Y stages in benchtop CNC mills using 1.8° bipolar stepper motors.

IC Role / Device Role / Timing Role: Full-bridge driver controlling single motor phase with eighth-step microstepping to achieve 0.225° effective step resolution and suppress 100–200 Hz mechanical resonance.

Use Value: Nonlinear DAC and mixed-decay mode maintain sinusoidal current waveforms across speed ranges, reducing audible noise and positional error caused by torque variation.

Use Scenario: Low-vibration, repeatable syringe actuation in portable infusion pumps delivering precise drug dosages over extended periods.

IC Role / Device Role / Timing Role: Motor winding controller implementing quarter- and eighth-step microstepping to minimize step-induced pulsation and ensure smooth fluid displacement.

Use Value: Internal thermal shutdown and UVLO prevent unintended motor motion during brown-out or overheating, supporting Class II medical device safety requirements.

Lab Automation Robotics

3D Printer Extruder Control

Use Scenario: Multi-axis robotic arm end-effector movement in automated sample handling systems requiring silent, jitter-free motion between discrete positions.

IC Role / Device Role / Timing Role: One of two A3955SLBTR drivers per motor (dual-winding control) executing microstepping sequences per Table 4 to generate coordinated sinusoidal phase currents.

Use Value: Slow-decay mode during current ramp-up and mixed-decay during ramp-down preserve current waveform fidelity, eliminating position lag during acceleration/deceleration profiles.

Use Scenario: High-resolution filament feed control in FDM 3D printers where extruder stepper motor must respond rapidly to G-code velocity commands without skipping steps.

IC Role / Device Role / Timing Role: Winding driver regulating current to ±1.5 A at 24 V supply, using fast-decay mode during rapid direction reversals to maintain closed-loop-like current tracking.

Use Value: 50 V rating and integrated clamp diodes tolerate inductive kickback from fast PWM transitions, improving reliability in compact, thermally constrained printer enclosures.

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 higher 2.5 A output current, integrated charge pump for 100% duty cycle, and improved thermal resistance (R_θJA = 40°C/W vs. 67°C/W).	Supports higher-torque stepper motors and higher ambient temperatures; requires updated PCB layout due to different pinout and charge pump capacitor placement.	Select A4975 for new designs requiring extended current capability, better thermal performance, or compatibility with Allegro's current-generation motor driver ecosystem.
TB6600HG	External PWM input architecture (vs. internal fixed-off-time), no integrated DAC, requires external current-sense amplifier and microcontroller-based step sequencing.	Offers greater flexibility in current control algorithm implementation but increases system-level design effort and component count.	Choose TB6600HG only if custom current profiling, variable microstep interpolation, or multi-motor synchronization via shared PWM clock is required.

Compared with A3955SLBTR, the A4975 provides higher current drive and superior thermal performance in a pin-incompatible package, while the TB6600HG shifts current control responsibility to the host MCU - making A4975 the preferred drop-in upgrade path for legacy A3955SLBTR designs where board redesign is feasible.

Availability

A3955SLBTR is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, lab automation robotics, and 3D printer extruder control requiring stable component supply for legacy system maintenance and repair.

Supply support for A3955SLBTR 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 ICs, specializing in motion control, current sensing, and motor driver solutions for industrial, automotive, and medical markets.

The A3955 product line was engineered specifically for bipolar stepper motor microstepping applications demanding low-noise, high-resolution positioning - emphasizing integrated current regulation, thermal robustness, and simplified system-level design.

FAQ

What is the functional status of the A3955SLBTR?

The A3955SLBTR is a discontinued product no longer in production as of January 30, 2012. Allegro MicroSystems explicitly states it should not be purchased for new design applications, and samples are no longer available. However, Aetrix Electronics maintains limited legacy inventory for repair and maintenance of existing systems still deployed in industrial and medical equipment.

Can the A3955SLBTR drive a full bipolar stepper motor by itself?

No, the A3955SLBTR drives only one winding of a bipolar stepper motor. A complete two-phase bipolar stepper motor requires two A3955SLBTR devices-one for each phase (winding A and winding B)-with coordinated PHASE and DAC inputs to generate the required sinusoidal current waveforms per Table 4 in the datasheet.

What does "nonlinear DAC" mean for the A3955SLBTR, and why is it used?

The A3955SLBTR's 3-bit nonlinear DAC outputs voltage steps (e.g., 19.5%, 38.2%, 55.5%, 70.7%, 83.1%, 92.4%, 100%) that approximate a sine function rather than equal increments. This matches the natural sinusoidal current profile needed for smooth microstepping, minimizing torque ripple and resonance-unlike linear DACs which produce uneven torque at fractional steps.

How does the PFD pin affect motor performance in the A3955SLBTR?

The PFD pin on the A3955SLBTR selects current-decay behavior: ≥3.5 V enables slow decay (low ripple, ideal for current ramp-up), ≤0.8 V enables fast decay (rapid current collapse, useful during direction reversal), and 1.1–3.1 V enables mixed decay-combining both to maintain regulation while limiting ripple. Incorrect PFD voltage causes current waveform distortion and step loss.

What thermal design considerations apply to the A3955SLBTR in SOICW (LB) package?

The A3955SLBTR in LB package has R_θJA = 67°C/W on a 2-layer PCB with 0.3 in² exposed copper per side. To sustain ±1.5 A continuous current, the PCB must provide adequate copper area tied to pins 4–5 and 12–13 (internally fused grounds), and ambient temperature must stay ≤85°C. Exceeding 150°C junction temperature triggers thermal shutdown with 15°C hysteresis.

A3955SLBTR 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 FAQ

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

Please submit a Request for Quotation (RFQ) for A3955SLBTR 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 reliable?

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

3.What payment methods are accepted for A3955SLBTR?

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

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for A3955SLBTR?

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

Once your A3955SLBTR 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?

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

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

All A3955SLBTR 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 meets industry standards.

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

All A3955SLBTR units undergo pre-shipment inspection (PSI). If there is an issue with A3955SLBTR, 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 part is unused and in its original packaging.

Return procedure for A3955SLBTR:

1.Submit a request within 90 days.

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

Tech Hub

2026-09-08 Obsolete Electronic Components: How to Source and Evaluate Replacements

A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.

2026-09-07 TTL vs CMOS Logic Levels: 74HC and 74HCT Compatibility Explained

TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.

2026-09-04 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-02 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…