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Allegro MicroSystems A3977SEDTR-T
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- Part No.:
- A3977SEDTR-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 44-LCC (J-Lead)
- Datasheet:
-
A3977SEDTR-T.pdf
- Description:
- IC MTR DRVR BIPOLR 3-5.5V 44PLCC
- Quantity:
- Payment:
- Shipping:
Inventory:2,975
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Product details
Overview
A3977SEDTR-T from Allegro MicroSystems is a complete bipolar stepper motor driver IC with integrated translator, supporting full-, half-, quarter-, and eighth-step microstepping modes. It delivers ±2.5 A output current at up to 35 V supply, features fixed off-time PWM current regulation with automatic mixed/fast/slow decay selection, and operates across 3.0–5.5 V logic supply - enabling precise motion control in compact industrial positioning systems.
For engineers reviewing the A3977SEDTR-T datasheet, A3977SEDTR-T pinout, A3977SEDTR-T application, or A3977SEDTR-T equivalent, key selection considerations include its 28-pin TSSOP-LP package with exposed thermal pad, synchronous rectification for reduced power dissipation, HOME output for position initialization, and step-resolution control via MS1/MS2 logic inputs without external sequencing logic.
Technical Context
The A3977SEDTR-T integrates dual N-channel DMOS H-bridges with on-chip translator and fixed off-time PWM current regulation. Its DAC-based current profiling enables precise microstep current waveforms per Table 2, while PFD input dynamically selects decay mode (slow/fast/mixed) based on step direction and voltage thresholds (0.21×VDD and 0.6×VDD).
Internal charge pump (CP1/CP2/VCP) generates gate drive above VBB for high-side N-MOSFETs; synchronous rectification (controlled by SR pin) replaces body diode conduction during decay, reducing power loss. Protection includes thermal shutdown (165°C, 15°C hysteresis), UVLO (2.7 V threshold), and crossover-current prevention.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Current | ±2.5 A continuous - supports high-torque bipolar stepper motors without external current amplification |
| Load Supply Voltage | 8–35 V - compatible with common industrial DC bus voltages including 12 V, 24 V, and 32 V systems |
| Logic Supply Range | 3.0–5.5 V - interoperable with 3.3 V and 5 V microcontrollers without level shifting |
| Microstep Resolution | Full / Half / Quarter / Eighth - selected via MS1/MS2 pins; eliminates need for external step-table memory or firmware sequencing |
| RDS(on) | 0.28 Ω source / 0.22 Ω sink typical - minimizes conduction loss and thermal rise at rated current |
| Fixed Off-Time | 38 µs typical (Rt=56 kΩ, Ct=680 pF) - sets minimum current decay duration for stable PWM regulation |
| Thermal Resistance | RθJA = 28 °C/W (4-layer PCB) - enables ≥4 W power dissipation with standard layout and thermal vias under exposed pad |
Pinout & Package
Package: 28-pin TSSOP with exposed thermal pad (LP suffix), thickness <1.2 mm, lead-free with 100% matte tin plating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SENSE1, SENSE2 | Current sense inputs | Connect to low-side sense resistors for phase 1 and phase 2; max 0.5 V input limits trip accuracy and thermal margin |
| OUT1A/OUT1B, OUT2A/OUT2B | H-bridge outputs | Drive bipolar stepper motor windings; each bridge handles ±2.5 A with N-MOSFET topology |
| STEP, DIR, MS1, MS2 | Translator control inputs | STEP advances one microstep; DIR sets rotation direction; MS1/MS2 configure resolution per truth table |
| PFD | Decay mode select | Voltage level (0.21×VDD to 0.6×VDD) determines fast/mixed/slow decay behavior during current reduction |
| HOME | Position indicator output | Active-low logic signal indicating translator home state - used for homing sequence validation |
| SLEEP, ENABLE | Power management inputs | SLEEP reduces quiescent current to 20 µA; ENABLE disables all bridges while preserving translator state |
| VCP, CP1, CP2 | Charge pump network | Generate gate drive >VBB for high-side N-MOSFETs; requires 0.22 µF ceramic capacitors per datasheet layout |
| AGND, PGND | Analog & power ground | Must be connected externally at single point near exposed thermal pad - critical for current-sense accuracy and thermal performance |
Key Features
| Feature | Design Value |
|---|---|
| Integrated translator | Eliminates need for microcontroller-based phase sequencing - STEP/DIR interface reduces firmware overhead in resource-constrained systems |
| Automatic decay mode selection | Dynamically chooses slow/fast/mixed decay per step transition to minimize BEMF-induced current distortion and audible noise |
| Synchronous rectification | Replaces body diodes with low-RDS(on) MOSFETs during decay, cutting power loss by >30% vs. passive rectification |
| Home output | Provides hardware-verified reference position at power-up/reset - enables deterministic startup without encoder feedback |
| Thermal & UVLO protection | Shuts down bridges at 165°C junction temp (15°C hysteresis) and disables operation below 2.7 V VDD - prevents latch-up and parametric failure |
Applications
| Industrial CNC Positioning | Medical Infusion Pumps |
|---|---|
Use Scenario: Precision linear actuation in multi-axis CNC tool changers requiring sub-0.9° step resolution and repeatable stall detection. IC Role / Device Role / Timing Role: Full-bridge driver with translator manages bipolar stepper phase currents and microstep sequencing independent of host controller timing. Use Value: Eighth-step mode (0.1125°/step) + ±2.5 A drive enables high-resolution motion with torque retention at low speeds - critical for smooth feed-rate transitions. | Use Scenario: Controlled syringe displacement in portable infusion pumps where silent operation and battery efficiency are mandatory. IC Role / Device Role / Timing Role: Translator-driven microstepping IC regulates motor current waveform shape to suppress mechanical resonance and audible coil whine. Use Value: Mixed-decay mode + synchronous rectification reduces audible noise by >15 dB(A) and extends battery life by lowering I²R losses during PWM decay cycles. |
| Automated Test Equipment (ATE) | 3D Printer Extruder Control |
Use Scenario: High-speed wafer prober stage indexing requiring rapid acceleration/deceleration with minimal positional overshoot. IC Role / Device Role / Timing Role: Fixed off-time current regulator maintains consistent phase current amplitude across 500 kHz STEP frequency range. Use Value: 500 kHz maximum STEP rate + HOME output allows sub-millisecond homing and synchronized multi-axis moves without host CPU intervention. | Use Scenario: Filament feed control in desktop 3D printers where compact board area and thermal management constrain design. IC Role / Device Role / Timing Role: TSSOP-LP packaged driver delivers ±2.5 A into stepper windings while dissipating heat through exposed thermal pad to PCB copper. Use Value: RθJA = 28 °C/W enables sustained 2.5 A operation on 4-layer boards with thermal vias - avoids derating or heatsinks in space-constrained extruder modules. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar stepper motor driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| TB6600HG | Higher voltage rating (44 V), but no integrated translator; requires external step/direction sequencer | Used where microcontroller has dedicated GPIO for phase control and higher bus voltage is needed | Select when system already implements translation logic and needs extended VBB range beyond 35 V |
| DRV8825 | Lower current rating (±1.5 A), same microstep modes, integrated translator, but no HOME output or PFD-controlled decay | Suitable for low-torque applications where position initialization and decay optimization are not required | Choose for cost-sensitive designs with ≤1.5 A load and no need for hardware homing or advanced decay tuning |
Compared with TB6600HG and DRV8825, the A3977SEDTR-T uniquely combines ±2.5 A drive, translator-based simplicity, HOME output for deterministic startup, and PFD-adjustable decay - making it optimal for industrial motion systems demanding both precision and robustness without added controller complexity.
Availability
A3977SEDTR-T is available at Aetrix Electronics and suitable for industrial CNC positioning, medical infusion pumps, automated test equipment, and 3D printer extruder control requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for A3977SEDTR-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 A3977 product line was designed specifically for cost-effective, high-accuracy bipolar stepper motor control in industrial automation and precision instrumentation - integrating translator, current regulation, and protection in a thermally optimized package.
FAQ
What is the maximum step frequency supported by the A3977SEDTR-T?
The A3977SEDTR-T supports a maximum STEP input frequency of 500 kHz, as specified in the Electrical Characteristics table. This allows high-speed microstepping operation while maintaining accurate current regulation. The actual achievable step rate depends on motor inductance, supply voltage, and decay mode configuration - but the IC guarantees proper sequencing and current control up to this rated frequency. For reliable operation, ensure STEP pulse width and hold time meet minimum timing requirements (1.0 µs each) per Figure 1.
How does the A3977SEDTR-T handle thermal protection?
The A3977SEDTR-T incorporates thermal shutdown circuitry that disables all output drivers when junction temperature reaches 165°C, with 15°C hysteresis to prevent oscillation. This protection is independent of external components and activates automatically during overload or poor heatsinking. Once cooled below 150°C, the device resumes normal operation after reset. The exposed thermal pad in the TSSOP-LP package is essential for effective heat transfer - Allegro specifies RθJA = 28 °C/W on a 4-layer PCB with thermal vias under the pad.
Can the A3977SEDTR-T drive unipolar stepper motors?
No, the A3977SEDTR-T is designed exclusively for bipolar stepper motors. Its dual full-bridge architecture drives current bidirectionally through each winding, which is required for bipolar operation. Unipolar steppers require center-tapped windings and single-polarity drive per phase - incompatible with the A3977SEDTR-T's H-bridge topology and current-sense architecture. Attempting to connect a unipolar motor may result in improper commutation, excessive heating, or damage.
What is the function of the PFD pin on the A3977SEDTR-T?
The PFD (Percent Fast Decay) pin on the A3977SEDTR-T sets the decay mode behavior during current reduction steps. When the STEP command lowers the DAC output, the voltage on PFD determines whether the bridge enters slow decay (>0.6×VDD), fast decay (<0.21×VDD), or mixed decay (between thresholds). This dynamic control minimizes current waveform distortion caused by motor back-EMF, improving step accuracy and reducing audible noise. A 0.1 µF capacitor to ground is required for stable operation.
Does the A3977SEDTR-T require external Schottky diodes?
No, the A3977SEDTR-T does not require external Schottky diodes due to its integrated synchronous rectification feature. When the SR pin is low, the IC actively turns on appropriate MOSFETs during current decay to bypass body diodes - reducing conduction loss and eliminating reverse recovery issues. External diodes are only needed if synchronous rectification is disabled (SR = high), typically for specialized power-dissipation redistribution, but this forfeits the efficiency and noise benefits of the internal scheme.
A3977SEDTR-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 44-LCC (J-Lead)
- 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 (4)
- Interface:
- Logic
- Technology:
- DMOS
- Step Resolution:
- 1, 1/2, 1/4, 1/8
- Applications:
- General Purpose
- Current - Output:
- 2.5A
- Voltage - Supply:
- 3V ~ 5.5V
- Voltage - Load:
- 8V ~ 35V
- Operating Temperature:
- -20°C ~ 150°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 44-PLCC (16.59x16.59)
A3977SEDTR-T FAQ
1.How can I place an order for A3977SEDTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A3977SEDTR-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 A3977SEDTR-T reliable?
The price and inventory of A3977SEDTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3977SEDTR-T is usually 5 days.
3.What payment methods are accepted for A3977SEDTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3977SEDTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A3977SEDTR-T?
A3977SEDTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A3977SEDTR-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 A3977SEDTR-T?
For technical support, including A3977SEDTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3977SEDTR-T requirements.
6.How does Aetrix verify that A3977SEDTR-T is sourced from the original manufacturer or authorized distributors?
All A3977SEDTR-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 A3977SEDTR-T meets industry standards.
7.What is the process for return or replacement of A3977SEDTR-T?
All A3977SEDTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A3977SEDTR-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 A3977SEDTR-T part is unused and in its original packaging.
Return procedure for A3977SEDTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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