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

Allegro MicroSystems A3977KLP

Name: A3977KLP
Brand: Allegro MicroSystems
SKU: A3977KLP
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: A3977KLP

Manufacturer:: Allegro MicroSystems

Category:: Motor Drivers, Controllers

Package:: 28-TSSOP (0.173", 4.40mm Width) Exposed Pad

Datasheet:: A3977KLP.pdf

Description:: IC MTR DRV BIPOLR 3-5.5V 28TSSOP

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Product details

Overview

A3977KLP from Allegro MicroSystems is a complete microstepping bipolar stepper motor driver IC with integrated translator, rated for 35 V and ±2.5 A output, supporting full-, half-, quarter-, and eighth-step modes. It features fixed off-time PWM current regulation, mixed/fast/slow decay control, and synchronous rectification to reduce audible noise and power dissipation in precision motion control systems.

For engineers reviewing the A3977KLP datasheet, A3977KLP pinout, A3977KLP application, or A3977KLP equivalent, key selection considerations include its 28-pin TSSOP-LP package with exposed thermal pad, logic supply range of 3.0–5.5 V, automatic decay mode detection, HOME output for position initialization, and R_DS(on) of 0.28 Ω (source) / 0.22 Ω (sink).

Technical Context

The A3977KLP implements dual N-channel DMOS H-bridges with fixed off-time PWM current regulation per phase, where trip current I_TRIP is set by external sense resistor R_S and reference voltage V_REF via I_TRIPmax = V_REF/8 × R_S. Decay mode (slow/fast/mixed) is dynamically selected based on step direction and PFD input voltage level relative to V_DD.

Its translator eliminates need for phase-sequence tables or high-frequency control lines: a single STEP pulse advances one microstep, with resolution determined by MS1/MS2 logic inputs. Internal charge pump (CP1/CP2/VCP) enables high-side N-MOSFET gate drive above V_BB, while synchronous rectification (controlled by SR pin) replaces body diode conduction to minimize power loss.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Current Rating	±2.5 A continuous per bridge - supports high-torque bipolar stepper motors up to 35 V supply
Logic Supply Range	3.0–5.5 V - compatible with 3.3 V and 5 V microcontrollers without level shifting
R_DS(on) (Source/Sink)	0.28 Ω / 0.22 Ω typical - reduces conduction loss and thermal load during PWM operation
Microstep Resolution	Full, half, quarter, eighth - selectable via MS1/MS2 pins; enables 1.8° motor to achieve 0.225° step accuracy
Fixed Off-Time	30–46 µs (typ. 38 µs with 56 kΩ/680 pF) - sets minimum current decay duration and regulates average current
Thermal Shutdown	165°C with 15°C hysteresis - protects against sustained overload or poor heatsinking without external circuitry
V_SENSE Max	0.5 V DC - defines maximum allowable sense voltage; limits peak current to prevent comparator saturation

Pinout & Package

The A3977KLP is supplied in a thin (≤1.2 mm) 28-pin TSSOP package with exposed thermal pad (suffix LP), optimized for surface-mount assembly and thermal performance on multilayer PCBs with thermal vias under the pad.

Pin/Terminal	Circuit Role	Design Meaning
SENSE1, SENSE2	Current sense inputs	Connect to low-side sense resistors for each H-bridge; 0.5 V max rating defines I_TRIP scaling
OUT1A/OUT1B, OUT2A/OUT2B	H-bridge outputs	Drive bipolar stepper motor windings; support bidirectional current flow up to ±2.5 A
STEP, DIR, MS1, MS2	Translator control inputs	STEP pulses advance microsteps; DIR sets rotation direction; MS1/MS2 select resolution per truth table
PFD	Percent fast-decay control	Voltage level (0.21×V_DD to 0.6×V_DD) selects slow/fast/mixed decay for improved current waveform fidelity
HOME	Logic output indicator	Active-low signal indicates translator home state at power-up/reset - used for mechanical homing verification
SLEEP, ENABLE	Power/control enable	SLEEP disables internal regulators and charge pump for <20 µA quiescent current; ENABLE overrides all outputs
VCP, CP1, CP2	Charge pump network	VCP is reservoir node; CP1/CP2 require 0.22 µF ceramic caps to generate >V_BB gate drive for high-side N-MOSFETs
AGND, PGND	Analog & power ground	Must be connected externally at star point under thermal pad - separates noise-sensitive analog references from high-current return paths

Key Features

Feature	Design Value
Integrated translator	Eliminates need for external sequencer or microcontroller firmware to manage phase currents - STEP/DIR interface simplifies system design
Automatic decay mode selection	Dynamically chooses slow/fast/mixed decay per step transition to maintain sinusoidal current waveform and reduce BEMF-induced distortion
Synchronous rectification	Replaces body diode conduction with low-R_DS(on) MOSFET paths during decay, cutting power loss and enabling higher efficiency without external Schottky diodes
Home output (HOME)	Provides hardware-verified position reference at power-up or RESET - critical for repeatable mechanical initialization in closed-loop or open-loop systems
Comprehensive protection	Includes thermal shutdown (165°C), UVLO (2.7 V enable threshold), crossover-current prevention, and fault-latched outputs - reduces need for external supervision circuits

Applications

Industrial CNC Positioning	Medical Infusion Pumps
Use Scenario: Precise linear actuation of tool carriages using 1.8° hybrid stepper motors with 1/8-step resolution. IC Role / Device Role / Timing Role: A3977KLP serves as the full-bridge driver and microstep sequencer, translating STEP pulses into accurate bipolar winding currents while managing decay dynamics. Use Value: Enables sub-micron positioning repeatability and low-vibration motion via eighth-step mode and mixed-decay control, reducing mechanical resonance in lead-screw systems.	Use Scenario: Controlled delivery of IV fluids using small-form-factor stepper-driven peristaltic pumps in portable medical devices. IC Role / Device Role / Timing Role: A3977KLP drives the bipolar stepper motor with precise current regulation and sleep-mode power gating to extend battery life. Use Value: Achieves ±2% flow rate accuracy across temperature via stable R_DS(on) and internal reference, while HOME output ensures consistent start position after power cycling.
Automated Test Equipment (ATE)	3D Printer Extruder Control
Use Scenario: High-speed indexing of probe cards or wafer handlers requiring rapid, jitter-free stepping at 200 kHz STEP rate. IC Role / Device Role / Timing Role: A3977KLP acts as the timing-critical motor interface, accepting STEP commands from FPGA-based motion controller and delivering clean current waveforms. Use Value: Supports 500 kHz maximum STEP frequency with 1 µs pulse width, enabling sub-millisecond move-and-settle cycles without microcontroller bottlenecks.	Use Scenario: Fine-grained filament feed control in desktop FDM printers using NEMA 17 stepper motors. IC Role / Device Role / Timing Role: A3977KLP provides eighth-step microstepping and synchronous rectification to minimize heat buildup in enclosed print heads. Use Value: Reduces motor heating by >30% versus discrete drivers due to 0.22 Ω sink R_DS(on) and active rectification, improving long-duration print reliability.

Industrial CNC Positioning

Medical Infusion Pumps

Use Scenario: Precise linear actuation of tool carriages using 1.8° hybrid stepper motors with 1/8-step resolution.

IC Role / Device Role / Timing Role: A3977KLP serves as the full-bridge driver and microstep sequencer, translating STEP pulses into accurate bipolar winding currents while managing decay dynamics.

Use Value: Enables sub-micron positioning repeatability and low-vibration motion via eighth-step mode and mixed-decay control, reducing mechanical resonance in lead-screw systems.

Use Scenario: Controlled delivery of IV fluids using small-form-factor stepper-driven peristaltic pumps in portable medical devices.

IC Role / Device Role / Timing Role: A3977KLP drives the bipolar stepper motor with precise current regulation and sleep-mode power gating to extend battery life.

Use Value: Achieves ±2% flow rate accuracy across temperature via stable R_DS(on) and internal reference, while HOME output ensures consistent start position after power cycling.

Automated Test Equipment (ATE)

3D Printer Extruder Control

Use Scenario: High-speed indexing of probe cards or wafer handlers requiring rapid, jitter-free stepping at 200 kHz STEP rate.

IC Role / Device Role / Timing Role: A3977KLP acts as the timing-critical motor interface, accepting STEP commands from FPGA-based motion controller and delivering clean current waveforms.

Use Value: Supports 500 kHz maximum STEP frequency with 1 µs pulse width, enabling sub-millisecond move-and-settle cycles without microcontroller bottlenecks.

Use Scenario: Fine-grained filament feed control in desktop FDM printers using NEMA 17 stepper motors.

IC Role / Device Role / Timing Role: A3977KLP provides eighth-step microstepping and synchronous rectification to minimize heat buildup in enclosed print heads.

Use Value: Reduces motor heating by >30% versus discrete drivers due to 0.22 Ω sink R_DS(on) and active rectification, improving long-duration print reliability.

Equivalent & Alternatives

The following parts are listed as comparable options for similar bipolar stepper motor driver applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
TB6600HG	Higher voltage rating (45 V), but no integrated translator; requires external step/direction sequencing logic	Lacks HOME output and automatic decay selection - demands more MCU resources and tuning effort	Choose when higher bus voltage or discrete control architecture is required; not drop-in for A3977KLP's translator-based interface
DRV8825	Lower current rating (±2.2 A), same 28-pin TSSOP package; includes indexer but no HOME output or PFD-controlled mixed decay	Missing hardware homing signal and advanced decay optimization - less suitable for safety-critical or low-noise applications	Consider for cost-sensitive designs where 2.2 A suffices and homing is handled externally; verify thermal margin at full load

Compared with TB6600HG and DRV8825, the A3977KLP uniquely combines translator-based simplicity, hardware HOME signaling, and PFD-adjustable mixed-decay control - making it optimal for applications demanding deterministic initialization, low acoustic noise, and minimal MCU overhead.

Availability

A3977KLP 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 A3977KLP 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 magnetic sensing, power ICs, and motion control solutions, with design centers in North America and manufacturing partnerships worldwide.

The A3977 product line delivers highly integrated stepper motor drivers with on-chip translators and intelligent current control, targeting applications needing precise, quiet, and reliable open-loop motion without complex firmware.

FAQ

What is the maximum STEP input frequency supported by the A3977KLP?

The A3977KLP supports a minimum guaranteed STEP frequency of 500 kHz, with electrical timing specifications requiring ≥1.0 µs pulse width and ≥1.0 µs low time. Operation above this value is possible but not warranted across temperature and voltage ranges. For robust 200 kHz operation common in CNC and printer applications, the A3977KLP provides ample timing margin and stable microstepping performance.

How does the A3977KLP handle thermal protection, and what happens when it triggers?

The A3977KLP incorporates thermal shutdown that activates at approximately 165°C junction temperature, with 15°C hysteresis. When triggered, all DMOS outputs are disabled, the translator resets to home state, and the HOME output goes low. Normal operation resumes only after junction temperature falls below ~150°C. This protection is internal and requires no external components, safeguarding the device during overload or inadequate heatsinking conditions.

Can the A3977KLP drive unipolar stepper motors?

No, the A3977KLP is designed exclusively for bipolar stepper motors. Its dual full-bridge architecture delivers bidirectional current through each winding, which is incompatible with the center-tapped configuration of unipolar motors. Attempting to connect a unipolar motor will result in improper phase excitation and potential damage. For unipolar applications, a dedicated unipolar driver or external H-bridge reconfiguration is required.

What is the purpose of the PFD pin on the A3977KLP, and how should it be configured?

The PFD (Percent Fast Decay) pin on the A3977KLP sets the decay mode behavior during current reduction steps. A voltage <0.21×V_DD selects fast decay; >0.6×V_DD selects slow decay; values between enable mixed decay. It must be decoupled with a 0.1 µF capacitor to ground. Proper PFD configuration minimizes current waveform distortion caused by motor back-EMF, directly improving step accuracy and reducing audible noise in the A3977KLP.

Is the A3977KLP RoHS-compliant and lead-free?

Yes, the A3977KLP is lead (Pb) free and fully RoHS-compliant. It features 100% matte tin plating on the leadframe and meets JEDEC J-STD-020 moisture sensitivity level 3 requirements. The device is qualified for reflow soldering per standard Pb-free profiles, and its TSSOP-LP package is compatible with automated SMT assembly processes used in high-reliability industrial and medical electronics manufacturing.

A3977KLP Specifications

Product attributes: Attribute value

Manufacturer:: Allegro MicroSystems

Series:: -

Package/Case:: 28-TSSOP (0.173", 4.40mm Width) Exposed Pad

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 (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:: -40°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 28-TSSOP-EP

A3977KLP FAQ

1.How can I place an order for A3977KLP through Aetrix?

Please submit a Request for Quotation (RFQ) for A3977KLP 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 A3977KLP reliable?

The price and inventory of A3977KLP are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3977KLP is usually 5 days.

3.What payment methods are accepted for A3977KLP?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3977KLP transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for A3977KLP?

A3977KLP orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your A3977KLP 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 A3977KLP?

For technical support, including A3977KLP datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3977KLP requirements.

6.How does Aetrix verify that A3977KLP is sourced from the original manufacturer or authorized distributors?

All A3977KLP 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 A3977KLP meets industry standards.

7.What is the process for return or replacement of A3977KLP?

All A3977KLP units undergo pre-shipment inspection (PSI). If there is an issue with A3977KLP, 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 A3977KLP part is unused and in its original packaging.

Return procedure for A3977KLP:

1.Submit a request within 90 days.

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

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