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Allegro MicroSystems A3955SLB-T
- Part No.:
- A3955SLB-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 16-PowerSOIC (0.295", 7.50mm Width)
- Datasheet:
-
A3955SLB-T.pdf
- Description:
- IC MTR DRV BIPLR 4.5-5.5V 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,663
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Product details
Overview
A3955SLB-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 for CNC equipment and precision positioning stages.
For engineers reviewing the A3955SLB-T datasheet, A3955SLB-T pinout, A3955SLB-T application, or A3955SLB-T equivalent, key selection considerations include its SOICW-16 (LB) package with internally fused pins, mixed/fast/slow current-decay mode selection via analog PFD input, thermal shutdown at 165°C, and discontinuation status requiring legacy design support or migration planning.
Technical Context
The A3955SLB-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. Its internal 3-bit nonlinear DAC sets eight discrete current ratios (19.5%–100%) by scaling VREF/3RS, enabling quarter- and eighth-step microstepping without external DACs.
Current decay behavior is user-selectable via analog PFD voltage: ≥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 initiates then transitions to slow decay-to balance ripple, regulation fidelity, and motor losses during bidirectional current slewing.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Current | ±1.5 A continuous - supports NEMA 17–23 stepper motors with adequate heatsinking |
| Load Voltage | 50 V max - compatible with 24 V and 48 V industrial motor supplies |
| Microstep Resolution | Eighth-step (1/8) - achieved via 3-bit nonlinear DAC with 8 discrete current ratios |
| PWM Off-Time | 18.2–22.3 μs (typ.) - set by external RT/CT; determines switching frequency and ripple |
| Current-Decay Modes | Slow, fast, or mixed - selected by analog PFD voltage; critical for torque smoothness and back-EMF handling |
| Junction Temp Limit | 165°C thermal shutdown - protects against sustained overload or poor PCB thermal design |
| Package Type | SOICW-16 (LB) - thermally enhanced 16-pin wide-body SOIC with internally fused pins |
Pinout & Package
Package: SOICW-16 (LB), 16-pin wide-body SOIC with internally fused pins 4–5 and 12–13; exposed thermal pad at ground potential; Pb-free matte tin plating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (PFD) | Analog current-decay mode control | Voltage input (0.8–3.5 V range) selects fast/mixed/slow decay; directly impacts torque ripple and regulation stability |
| 2 (REF) | Reference voltage input | Combined with RS and DAC bits to set ITRIP ≈ VREF / 3RS; defines peak winding current |
| 3 (RC) | RC timing node | Connects external RT and CT to set PWM off-time and comparator blanking duration |
| 4–5, 12–13 (GROUND) | Power return | Internally fused ground paths for logic (VCC) and load (VBB); shared reference for all measurements |
| 6 (VCC) | Logic supply | 4.5–5.5 V input powering internal logic; requires local 47 µF decoupling |
| 7 (PHASE) | Winding polarity control | Digital input determining current direction (H = OUTA high/OUTB low; L = reverse) |
| 8–9, 14 (D2, D1, D0) | DAC data inputs | 3-bit nonlinear code selecting one of eight current ratios (0%–100%) for microstepping |
| 10 (OUTA), 15 (OUTB) | Full-bridge outputs | High-side and low-side drive terminals connecting to stepper motor winding ends |
| 11 (SENSE) | Current-sense return | Connects to low-side of external sense resistor RS; feeds current-sense comparator |
| 16 (VBB) | Load supply | 5–50 V motor power input; routed separately from logic ground to minimize noise coupling |
Key Features
| Feature | Design Value |
|---|---|
| Internal PWM current control | Fixed-off-time architecture eliminates need for external current-sense amplifier or PWM generator |
| 3-bit nonlinear DAC | Provides eight precisely stepped current ratios (19.5%–100%) matching sinusoidal microstepping profiles |
| Selectable current-decay modes | Slow/fast/mixed decay via single analog PFD input enables optimization for torque smoothness vs. regulation fidelity |
| Integrated protection | Thermal shutdown (165°C), UVLO (3.7 V threshold), crossover-current delay (1 µs), and clamp diodes reduce BOM count |
| SOICW-16 (LB) package | Thermally enhanced layout with fused ground pins simplifies PCB layout and improves thermal resistance (RθJA = 67°C/W) |
Applications
| Industrial CNC Positioning | Medical Infusion Pumps |
|---|---|
Use Scenario: High-precision linear actuation in multi-axis CNC milling machines requiring sub-micron repeatability and minimal vibration. IC Role / Device Role / Timing Role: Full-bridge driver controlling one phase of a bipolar stepper motor; regulates sinusoidal winding current using eighth-step microstepping and mixed-decay mode. Use Value: Reduces resonance and torque variation at low speeds, enabling smooth feed rates below 10 RPM without step loss. |
Use Scenario: Accurate, quiet fluid delivery in portable infusion pumps where audible noise and mechanical jitter must be minimized. IC Role / Device Role / Timing Role: Motor phase controller implementing quarter-step microstepping with slow-decay mode during current ramp-up to limit EMI and acoustic noise. Use Value: Achieves <25 dB(A) acoustic output and <0.1% flow rate error over battery life by suppressing current ripple and commutation spikes. |
| Laboratory Automation Stages | 3D Printer Extruder Control |
Use Scenario: Sub-micron sample positioning in automated microscopy stages requiring zero missed steps during acceleration/deceleration. IC Role / Device Role / Timing Role: Winding driver using dynamic PFD voltage modulation to switch between slow decay (ramp-up) and mixed decay (ramp-down) per microstep. Use Value: Maintains position accuracy within ±0.05° over 10⁶ cycles by preventing back-EMF-induced current tailing during direction reversal. |
Use Scenario: Filament feed control in desktop 3D printers where compact size and thermal robustness are critical in enclosed enclosures. IC Role / Device Role / Timing Role: Compact SOICW-16 stepper driver operating at 24 V with thermal shutdown and internal clamp diodes eliminating external TVS components. Use Value: Enables board-level integration without heatsinks while sustaining 1.5 A continuous current at 60°C ambient via fused ground thermal path. |
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 current rating, integrated charge pump, and improved thermal performance (RθJA = 40°C/W); supports same microstepping modes. | Designed for new designs requiring higher torque density and extended temperature operation (–40°C to 125°C). | Recommended for all new designs; pinout differs, requiring PCB revision but offering superior thermal headroom and current capability. |
| TB6600HG | External oscillator-based PWM; no integrated DAC; requires external current-sense amplifier and microcontroller-driven step/direction interface. | Targeted at cost-sensitive, lower-precision applications where microcontroller handles all sequencing and current profiling. | Appropriate when existing firmware already manages microstepping waveforms and external sensing is acceptable; lacks A3955SLB-T's analog PFD flexibility and integrated protection. |
Compared with A3955SLB-T, the A4975 delivers higher current and better thermal metrics in a pin-different package, while the TB6600HG shifts complexity to the MCU but reduces BOM cost-making A4975 ideal for performance upgrades and TB6600HG suitable for firmware-flexible, cost-driven implementations.
Availability
A3955SLB-T is available at Aetrix Electronics and suitable for legacy industrial motion control, medical device repair, and laboratory equipment maintenance requiring stable component supply despite end-of-life status.
Supply support for A3955SLB-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 semiconductor company specializing in high-performance magnetic sensing and power ICs for motion control and energy-efficient systems.
The A3955 product line was engineered for precision bipolar stepper motor microstepping in industrial automation and medical instrumentation, emphasizing analog current control fidelity and integrated protection.
FAQ
Is the A3955SLB-T still in production?
No, the A3955SLB-T is a discontinued product. Allegro MicroSystems ceased production on January 30, 2012. It is not recommended for new designs. Aetrix Electronics maintains limited legacy stock for repair and maintenance of existing equipment, with full traceability and documentation support for the A3955SLB-T.
What is the difference between A3955SLB-T and A3955SB-T?
The A3955SLB-T uses a 16-pin SOICW (LB) package with internally fused ground pins, while the A3955SB-T uses a 16-pin DIP (B) package with exposed copper thermal tabs. Both share identical electrical specifications, pin numbering, and functional behavior-the only differences are mechanical form factor and thermal characteristics (RθJA = 67°C/W vs. 43°C/W).
Can the A3955SLB-T drive a full bipolar stepper motor?
No-the A3955SLB-T drives only one winding (phase) of a bipolar stepper motor. A complete two-phase bipolar stepper motor requires two A3955SLB-T devices-one for each winding-configured with coordinated PHASE and DAC inputs to generate sinusoidal current waveforms as shown in the official step sequencing table.
What does "mixed decay" mean for the A3955SLB-T?
Mixed decay in the A3955SLB-T refers to a user-configurable current-decay mode where the off-time is split: an initial fast-decay period (both source and sink drivers off) followed by slow-decay recirculation (sink driver on). This balances regulation accuracy-especially during current decrease-with reduced ripple and motor losses, and is selected by applying 1.1–3.1 V to the PFD pin.
Does the A3955SLB-T require external current-sense resistors?
Yes-the A3955SLB-T requires an external sense resistor (RS) connected between SENSE (pin 11) and ground. The value of RS, combined with VREF and DAC inputs, determines the peak output current via ITRIP ≈ VREF / 3RS. Typical values range from 0.25 Ω to 1.0 Ω depending on desired current and thermal constraints.
A3955SLB-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 16-PowerSOIC (0.295", 7.50mm Width)
- 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:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
A3955SLB-T FAQ
1.How can I place an order for A3955SLB-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A3955SLB-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 A3955SLB-T reliable?
The price and inventory of A3955SLB-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3955SLB-T is usually 5 days.
3.What payment methods are accepted for A3955SLB-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3955SLB-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A3955SLB-T?
A3955SLB-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A3955SLB-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 A3955SLB-T?
For technical support, including A3955SLB-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3955SLB-T requirements.
6.How does Aetrix verify that A3955SLB-T is sourced from the original manufacturer or authorized distributors?
All A3955SLB-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 A3955SLB-T meets industry standards.
7.What is the process for return or replacement of A3955SLB-T?
All A3955SLB-T units undergo pre-shipment inspection (PSI). If there is an issue with A3955SLB-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 A3955SLB-T part is unused and in its original packaging.
Return procedure for A3955SLB-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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