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Allegro MicroSystems A4945KLJTR-T
- Part No.:
- A4945KLJTR-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
A4945KLJTR-T.pdf
- Description:
- IC FAN DRIVER BLDC 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,353
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Product details
Overview
A4945KLJTR-T from Allegro MicroSystems is a three-phase sensorless sinusoidal fan driver IC in an 8-pin SOICN package with exposed thermal pad (LJ), designed for medium-power brushless DC fans. It features analog speed control via VSP pin, 180° sinusoidal drive (28–32 kHz PWM output), overcurrent protection (1.6 A typical), and operates across –40°C to +125°C ambient temperature.
For engineers reviewing the A4945KLJTR-T datasheet, A4945KLJTR-T pinout, A4945KLJTR-T application, or A4945KLJTR-T equivalent, key selection considerations include its K-temperature grade, LJ thermal-pad package, analog speed input architecture, FG tachometer output, and discontinuation status requiring transition planning.
Technical Context
The A4945KLJTR-T implements a proprietary sensorless commutation algorithm that uses back-EMF detection on phase A during a narrow window to estimate rotor position and generate synchronized 120°-phase-shifted sinusoidal modulation profiles. Its trapezoidal startup sequence transitions automatically to sinusoidal operation once motor speed reaches ~50% target.
Speed demand is digitized as a 9-bit value from the analog VSP input (0.45–1.2 V threshold, ±6 LSB accuracy), then mapped to internal PWM duty cycle generation. Protection includes lock detection (7–9 s auto-restart timeout), thermal shutdown (150–180°C trip), and supply UVLO (3.85–3.98 V with 150–450 mV hysteresis).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 4 V to 18 V - supports legacy 5 V/12 V systems and enables voltage-mode speed control down to 4 V without external regulators. |
| Operating Ambient Temperature | –40°C to +125°C - qualified for high-temperature industrial and automotive under-hood fan applications. |
| Motor PWM Frequency | 28–32 kHz - ultrasonic switching minimizes audible noise and EMI in fan systems. |
| Overcurrent Limit (OCL) | 1.4–1.8 A - internally sensed high-side current limiting protects MOSFETs and motor windings during stall or overload. |
| VSP Input Threshold | 0.45–1.2 V (on), 194–264 mV (off) - precise analog speed command with hysteresis prevents oscillation near turn-on/off points. |
| Total RDS(on) | 1.1–1.4 Ω @ 12 V, 25°C - low conduction loss improves efficiency and reduces thermal load in continuous fan operation. |
| FG Output Type | Open-drain logic-level signal - provides one pulse per electrical revolution for accurate tachometer feedback to host controller. |
Pinout & Package
Package: 8-pin SOICN with exposed thermal pad (LJ), Pb-free with 100% matte-tin leadframe plating. Thermal resistance RθJA = 62°C/W on 2-layer PCB with 0.8 in² copper per side.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 GND | Ground reference | Primary power and signal return; must be connected to thermal pad for optimal heat dissipation. |
| 2 OUTA | Motor phase A output | High- and low-side gate-driven terminal for 3-phase BLDC motor winding connection. |
| 3 VBB | Main power supply input | Accepts 4–18 V DC; powers internal regulators, drivers, and logic; requires CVBB capacitor (4.7–47 µF). |
| 4 VSP | Analog speed command input | 0–3.05 V analog input; internal 100 kΩ pulldown ensures safe disable if floating; enables system-level speed control without variable PSU. |
| 5 VREF | Analog reference output | 3.2–3.4 V regulated output; supplies bias for external components and serves as precision reference for VSP scaling. |
| 6 FG | Fan speed feedback output | Open-drain tachometer signal - one pulse per electrical revolution; requires external pullup (e.g., 20 kΩ to VBB). |
| 7 OUTC | Motor phase C output | High- and low-side gate-driven terminal; complements OUTA/OUTB for full 3-phase drive. |
| 8 OUTB | Motor phase B output | High- and low-side gate-driven terminal; completes 3-phase output set with 120° phase relationship. |
| PAD | Exposed thermal pad | Internally connected to GND; must be soldered to PCB ground plane with thermal vias for reliable thermal performance. |
Key Features
| Feature | Design Value |
|---|---|
| 180° sinusoidal drive | Reduces torque ripple and acoustic noise by generating smooth current waveforms instead of trapezoidal commutation. |
| Sensorless BEMF position detection | Eliminates Hall sensors or encoders - detects rotor position using back-EMF on phase A during controlled timing windows. |
| Soft-start current ramp | Gradually increases speed demand and current limit at startup to prevent inrush current and mechanical shock to fan assembly. |
| Integrated lock detection & auto-restart | Disables outputs for 7–9 seconds upon rotor lock detection, then attempts automatic recovery - avoids permanent fault latch-up. |
| Thermal shutdown with hysteresis | Shuts down at 150–180°C junction temperature and remains off until temperature drops ≥20°C below trip point. |
Applications
| Server Cooling Fan | Industrial HVAC Blower |
|---|---|
|
Use Scenario: High-reliability 48 V server rack cooling with variable-speed demand based on CPU thermal telemetry. IC Role / Device Role / Timing Role: Three-phase BLDC motor driver executing sensorless sinusoidal commutation with FG-based closed-loop speed regulation. Use Value: Enables quiet, efficient fan operation across wide thermal loads while meeting datacenter acoustic and energy-efficiency requirements. |
Use Scenario: Variable-air-volume (VAV) box in commercial HVAC system requiring robust fan control in dusty, high-temperature environments. IC Role / Device Role / Timing Role: Motor driver providing analog speed command interface, thermal protection, and tach feedback for building management system integration. Use Value: Supports extended operating range (–40°C to +125°C ambient) and withstands voltage transients common in industrial power distribution. |
| Medical Ventilator Air Pump | Automotive Cabin Fan |
|
Use Scenario: Precision airflow delivery in portable ventilators where audible noise and vibration must be minimized for patient comfort. IC Role / Device Role / Timing Role: Sinusoidal fan driver delivering smooth torque and low-noise operation via 30 kHz PWM switching and adaptive BEMF sensing. Use Value: Meets stringent acoustic specifications (<30 dBA) while maintaining speed accuracy and reliability under battery-powered conditions. |
Use Scenario: Climate control blower in passenger compartment, operating across vehicle battery voltage (9–16 V) and under-hood temperature extremes. IC Role / Device Role / Timing Role: Motor driver with UVLO, overcurrent, and thermal protection ensuring fail-safe behavior during cold cranking or thermal overload events. Use Value: Qualified for automotive-grade temperature range and integrates protection features eliminating need for discrete fault monitoring circuitry. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar three-phase sensorless fan driver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| A5947KLPTR-T | Successor device with enhanced thermal performance (RθJA = 48°C/W), wider VBB range (3.3–28 V), and integrated 5 V LDO for external logic. | Supports higher-power fans and direct connection to 24 V HVAC systems; replaces A4945KLJTR-T in new designs per Allegro's transition guidance. | Select for new designs requiring extended voltage range, improved thermal margin, or integrated regulator functionality. |
| A4945GLJTR-T | Same functional architecture and pinout, but rated for –40°C to +105°C ambient and discontinued as of September 2024. | Limited to lower-temperature industrial applications; not suitable for +125°C environments like under-hood automotive use. | Only acceptable for legacy repair or inventory burn-down; lacks K-temperature qualification and long-term supply assurance. |
Compared with A4945KLJTR-T, A5947KLPTR-T offers higher voltage tolerance, better thermal efficiency, and active production status, while A4945GLJTR-T shares identical drive topology but lacks extended temperature capability and is no longer available for new designs.
Availability
A4945KLJTR-T is available at Aetrix Electronics and suitable for server cooling, industrial HVAC, medical ventilator air pumps, and automotive cabin fan applications requiring stable component supply during end-of-life transition phases.
Supply support for A4945KLJTR-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 and manufacturer of high-performance magnetic sensing and power IC solutions, specializing in motion control and energy-efficient semiconductor devices.
The A4945KLJTR-T belongs to Allegro's three-phase sensorless fan driver product line, engineered specifically to replace noisy, inefficient brushed DC fans in demanding thermal management systems with silent, high-efficiency BLDC alternatives.
FAQ
Is the A4945KLJTR-T still in production?
No, the A4945KLJTR-T has been officially discontinued by Allegro MicroSystems since December 28, 2019. Samples are no longer available, and it is designated as Last Time Buy with no future manufacturing planned. Aetrix Electronics maintains limited legacy stock for continuity support, but new designs should migrate to the recommended successor A5947KLPTR-T.
What is the function of the VSP pin on the A4945KLJTR-T?
The VSP pin on the A4945KLJTR-T is an analog speed input that accepts a 0–3.05 V signal to control fan speed. It features internal 100 kΩ pulldown, 0.45–1.2 V turn-on threshold, and ±6 LSB accuracy. The A4945KLJTR-T converts this voltage into a 9-bit demand value used to modulate the 30 kHz sinusoidal PWM outputs - enabling precise, low-noise speed regulation without external power supply adjustment.
Does the A4945KLJTR-T require external components for basic operation?
Yes, the A4945KLJTR-T requires two mandatory external capacitors: CVBB (4.7–47 µF) on VBB for supply stabilization and CVREF (0.1 µF X5R 10 V) on VREF for internal reference filtering. Optional components include RFG (20 kΩ pullup for FG), RPWM (1 kΩ noise isolation), and RPU (50 kΩ pullup to VBB for open-circuit speed override). Layout must include thermal vias under the exposed pad.
How does the A4945KLJTR-T achieve sensorless commutation?
The A4945KLJTR-T achieves sensorless commutation by sampling back-EMF voltage on phase A during precisely timed "detection windows" within the PWM cycle. Its internal algorithm interprets zero-crossing events to estimate rotor position and dynamically adjusts the 120°-phase-shifted sinusoidal modulation profiles applied to OUTA, OUTB, and OUTC - eliminating need for Hall sensors while maintaining smooth torque and low acoustic noise.
What protection features are integrated into the A4945KLJTR-T?
The A4945KLJTR-T integrates six core protections: (1) overcurrent limiting (1.4–1.8 A), (2) thermal shutdown (150–180°C with 20°C hysteresis), (3) VBB undervoltage lockout (3.85–3.98 V), (4) lock detection with 7–9 s auto-restart, (5) short-circuit detection on motor outputs, and (6) soft-start current ramping. These ensure robust operation in harsh thermal and electrical environments without external supervision circuitry.
A4945KLJTR-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Motor Type - Stepper:
- Multiphase
- Motor Type - AC, DC:
- Brushless DC (BLDC)
- Function:
- Fan Control
- Output Configuration:
- Half Bridge (3)
- Interface:
- Analog
- Technology:
- Power MOSFET
- Step Resolution:
- -
- Applications:
- Fan Motor Driver
- Current - Output:
- 1.8A
- Voltage - Supply:
- 4V ~ 18V
- Voltage - Load:
- -
- Operating Temperature:
- -40°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC-EP
A4945KLJTR-T FAQ
1.How can I place an order for A4945KLJTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A4945KLJTR-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 A4945KLJTR-T reliable?
The price and inventory of A4945KLJTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A4945KLJTR-T is usually 5 days.
3.What payment methods are accepted for A4945KLJTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A4945KLJTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A4945KLJTR-T?
A4945KLJTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A4945KLJTR-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 A4945KLJTR-T?
For technical support, including A4945KLJTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A4945KLJTR-T requirements.
6.How does Aetrix verify that A4945KLJTR-T is sourced from the original manufacturer or authorized distributors?
All A4945KLJTR-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 A4945KLJTR-T meets industry standards.
7.What is the process for return or replacement of A4945KLJTR-T?
All A4945KLJTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A4945KLJTR-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 A4945KLJTR-T part is unused and in its original packaging.
Return procedure for A4945KLJTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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