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Allegro MicroSystems A3955SB-T
- Part No.:
- A3955SB-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 16-PowerDIP (0.300", 7.62mm)
- Datasheet:
-
A3955SB-T.pdf
- Description:
- IC MTR DRV BIPOLR 4.5-5.5V 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,953
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Product details
Overview
A3955SB-T from Allegro MicroSystems is a discontinued full-bridge PWM microstepping motor driver IC designed to control one winding of a bipolar stepper motor in eighth-step microstepping mode, delivering ±1.5 A continuous output current at up to 50 V load supply, with internal 3-bit nonlinear DAC, selectable fast/slow/mixed current-decay modes, and integrated thermal shutdown - used in precision motion control for industrial automation and medical positioning systems.
For engineers reviewing the A3955SB-T datasheet, A3955SB-T pinout, A3955SB-T application, or A3955SB-T equivalent, this page delivers verified technical context, exact pin functions, confirmed microstepping step resolution (eighth-step), real-world decay-mode trade-offs, and two validated alternative drivers for legacy design migration.
Technical Context
The A3955SB-T implements fixed-off-time PWM current regulation using an external RT/CT network to set tOFF (18.2–22.3 μs typical), with blanking time synchronized to CT charging. Its 3-bit nonlinear DAC sets eight discrete output current ratios (19.5% to 100%) via D0–D2 inputs, enabling quarter- and eighth-step microstepping without external DAC circuitry.
Current decay behavior is user-configured via analog PFD input: ≥3.5 V enables slow decay (recirculating), ≤0.8 V enables fast decay (regenerative), and 1.1–3.1 V enables mixed decay - where fast decay occupies a user-determined percentage of tOFF before switching to slow decay, optimizing ripple vs. regulation in sinusoidal drive profiles.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Current | ±1.5 A continuous - defines maximum winding current capability without forced cooling under specified thermal conditions. |
| Load Supply Voltage | 50 V max - supports stepper motors requiring high-voltage operation while maintaining safe margin over typical 24–48 V industrial rails. |
| Microstepping Resolution | Eighth-step - achieves 8× finer angular resolution than full-step mode, reducing low-speed resonance and torque ripple. |
| PWM Off-Time Range | 18.2–22.3 μs (RT=43 kΩ, CT=470 pF) - directly sets minimum current-regulation cycle period and influences audible noise and EMI profile. |
| Current-Decay Modes | Slow, fast, and mixed - selectable via analog PFD voltage to balance current regulation accuracy, motor losses, and back-EMF compensation. |
| DAC Architecture | 3-bit nonlinear - provides non-uniform current steps (19.5%, 38.2%, 55.5%, 70.7%, 83.1%, 92.4%, 100%) optimized for sinusoidal microstepping fidelity. |
| Thermal Shutdown | 165°C activation with 15°C hysteresis - protects die during overload or inadequate heatsinking; resumes operation only after junction cools to ~150°C. |
Pinout & Package
Package: 16-pin DIP with exposed thermal tabs (suffix 'B'), lead-free matte tin plating, thermally enhanced pins electrically tied to ground.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (PFD) | Analog decay-mode selector | Voltage level (≤0.8 V / 1.1–3.1 V / ≥3.5 V) configures fast / mixed / slow current decay for optimal microstepping waveform fidelity. |
| 2 (REF) | Reference voltage input | Combined with RS and DAC bits, sets ITRIP ≈ VREF/(3 × RS) - primary analog control for peak winding current calibration. |
| 3 (RC) | Timing network node | Connects external RT and CT to define PWM off-time (tOFF ≈ RTCT) and comparator blanking duration. |
| 4–5, 12–13 (GROUND) | Power return | Common reference for logic (VCC) and load (VBB) supplies; thermally enhanced pins require no isolation as they are at ground potential. |
| 6 (VCC) | Logic supply | 4.5–5.5 V input powering internal logic, DAC, comparators, and gate drivers - must be decoupled locally. |
| 7 (PHASE) | Winding polarity control | Digital input selecting current direction in the motor winding (H = OUTA high/OUTB low; L = OUTA low/OUTB high). |
| 8–9, 14 (D2, D1, D0) | DAC data inputs | 3-bit parallel interface setting nonlinear current ratio (19.5%–100%) - all low disables outputs. |
| 10 (OUTA), 15 (OUTB) | Full-bridge outputs | High-current terminals connecting to one stepper motor winding; rated for ±1.5 A and 50 V with integrated clamp diodes. |
| 11 (SENSE) | Current-sense return | Connects to low-side sense resistor (RS) - voltage here (IOUT × RS) compared against DAC output to regulate current. |
| 16 (VBB) | Load supply | 5–50 V power input for motor winding; separate from logic supply to enable wide voltage range operation. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated transient-suppression diodes | Eliminates need for external flyback diodes across motor winding, reducing BOM count and PCB area in full-bridge layout. |
| User-selectable current-decay modes | Enables dynamic optimization of current regulation vs. motor/driver losses by configuring PFD voltage - critical for stable sinusoidal microstepping. |
| Nonlinear 3-bit DAC | Delivers precisely spaced current ratios matching sine-wave amplitude steps, minimizing quantization error in eighth-step microstepping profiles. |
| Internal thermal shutdown with hysteresis | Automatically disables outputs at 165°C and re-enables only after cooling to ~150°C - prevents thermal runaway while allowing recovery without system reset. |
| Crossover-current and UVLO protection | Prevents shoot-through during PHASE transitions and blocks operation below 3.35 V VCC, ensuring robust startup and fault-free switching. |
Applications
| Industrial CNC Positioning | Medical Infusion Pump Actuation |
|---|---|
|
Use Scenario: Precision open-loop positioning of linear stages in benchtop CNC mills using 1.8° bipolar stepper motors. IC Role / Device Role / Timing Role: Full-bridge driver controlling single motor winding in eighth-step microstepping mode, synchronized to step/direction pulses from motion controller. Use Value: Reduces low-speed vibration and resonance by increasing effective step resolution 8×, enabling smooth feed rates down to 0.1 mm/sec without closed-loop feedback. |
Use Scenario: Silent, accurate dosing control in portable IV infusion pumps requiring sub-milliliter per hour flow rates. IC Role / Device Role / Timing Role: Winding driver implementing sinusoidal current profiling to minimize audible motor noise and mechanical cogging during slow-speed operation. Use Value: Mixed-decay mode maintains tight current regulation during decreasing current phases, preventing back-EMF-induced current tailing that causes dosage inaccuracy. |
| Lab Automation Robotic Arms | Printed Circuit Board Router |
|
Use Scenario: Multi-axis articulated arm in automated test equipment moving optical sensors between measurement points on PCBs. IC Role / Device Role / Timing Role: One of two A3955SB-T devices per axis driving independent motor windings with coordinated PHASE and DAC sequencing. Use Value: Nonlinear DAC steps match theoretical sine-wave amplitudes, achieving >95% torque linearity across microstep positions - critical for repeatable endpoint accuracy. |
Use Scenario: High-speed X-Y gantry in desktop PCB milling machines routing traces with 0.2 mm feature resolution. IC Role / Device Role / Timing Role: Full-bridge driver operating in quarter-step mode with fast-decay selected during rapid direction reversals to maintain current regulation at 200+ steps/sec. Use Value: Fast current decay minimizes current lag during direction changes, preserving positional accuracy and preventing step loss under dynamic load. |
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 N-channel MOSFET gate drive, and improved thermal performance in SOIC package. | Supports higher-torque stepper motors and enables more compact board layouts due to reduced external component count. | Select A4975 for new designs requiring higher current, better efficiency, or SOIC footprint compatibility. |
| TB6600HG | 2-phase bipolar driver with built-in oscillator, 3.5 A rating, and 1/1 to 1/32 step resolution - lacks analog PFD control and uses digital decay-mode selection. | Offers wider microstepping range but requires external clock or step pulses; less flexible for custom sinusoidal waveform shaping. | Choose TB6600HG when standardized step resolution and integrated clock simplify system timing, and higher current headroom is needed. |
Compared with A3955SB-T, the A4975 provides higher current capability and modern gate-drive architecture for improved efficiency, while the TB6600HG offers broader step resolution and integrated clocking at the cost of analog decay-mode flexibility - both require PCB layout revision and firmware adaptation.
Availability
A3955SB-T is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pump actuation, lab automation robotic arms, and printed circuit board router applications requiring stable component supply for legacy system maintenance and repair.
Supply support for A3955SB-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 ICs, specializing in motion control, current sensing, and motor driver solutions since 1997.
The A3955SB-T belongs to Allegro's full-bridge PWM microstepping driver product line, engineered specifically for high-fidelity sinusoidal current control in bipolar stepper motor applications demanding low acoustic noise and minimal resonance.
FAQ
Is the A3955SB-T still in production?
No, the A3955SB-T is a discontinued product. Allegro officially ended production on January 30, 2012, and it is not recommended for new design applications. Aetrix Electronics maintains limited legacy stock for repair and maintenance of existing systems, with full traceability and documentation support for each unit shipped as A3955SB-T.
What package type does the A3955SB-T use?
The A3955SB-T uses a 16-pin dual-in-line plastic package (DIP) with exposed copper thermal tabs (suffix 'B'), compliant with JEDEC MS-001 BB. The thermally enhanced pins are internally connected to ground and require no electrical isolation - enabling direct mounting to heatsinks or copper pour areas on single-layer PCBs.
How does the A3955SB-T achieve eighth-step microstepping?
The A3955SB-T achieves eighth-step microstepping through its internal 3-bit nonlinear digital-to-analog converter, which generates seven precise current ratios (19.5%, 38.2%, 55.5%, 70.7%, 83.1%, 92.4%, 100%) plus zero - combined with PHASE input sequencing and external RC timing, enabling true sinusoidal current profiling across 8 discrete steps per full step.
Can the A3955SB-T drive a unipolar stepper motor?
No, the A3955SB-T is designed exclusively for bipolar stepper motors. Its full-bridge topology requires two leads per winding and relies on bidirectional current flow controlled by PHASE and DAC inputs - unipolar motors use center-tapped windings and require different switching topologies not supported by the A3955SB-T.
What is the function of the PFD pin on the A3955SB-T?
The PFD (Percent Fast Decay) pin on the A3955SB-T is an analog input that determines current-decay behavior: ≤0.8 V selects fast decay, 1.1–3.1 V selects mixed decay, and ≥3.5 V selects slow decay. This enables real-time optimization of current regulation accuracy, motor losses, and back-EMF compensation - a key differentiator for stable microstepping performance in the A3955SB-T.
A3955SB-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 16-PowerDIP (0.300", 7.62mm)
- Packaging:
- Tube
- 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:
- Through Hole
- Supplier Device Package:
- 16-DIP
A3955SB-T FAQ
1.How can I place an order for A3955SB-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A3955SB-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 A3955SB-T reliable?
The price and inventory of A3955SB-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3955SB-T is usually 5 days.
3.What payment methods are accepted for A3955SB-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3955SB-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A3955SB-T?
A3955SB-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A3955SB-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 A3955SB-T?
For technical support, including A3955SB-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3955SB-T requirements.
6.How does Aetrix verify that A3955SB-T is sourced from the original manufacturer or authorized distributors?
All A3955SB-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 A3955SB-T meets industry standards.
7.What is the process for return or replacement of A3955SB-T?
All A3955SB-T units undergo pre-shipment inspection (PSI). If there is an issue with A3955SB-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 A3955SB-T part is unused and in its original packaging.
Return procedure for A3955SB-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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