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Allegro MicroSystems A4949GLJTR-T
- Part No.:
- A4949GLJTR-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
A4949GLJTR-T.pdf
- Description:
- IC FAN DRIVER BLDC 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,400
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Product details
Overview
A4949GLJTR-T from Allegro MicroSystems is a three-phase sensorless sinusoidal fan driver IC designed for medium-power brushless DC (BLDC) fans. It features PWM speed input, 30 kHz motor PWM frequency, 1.1 Ω typical RDS(on), –40°C to 105°C operating ambient temperature, and integrated lock detection with 8 s auto-restart - enabling low-noise, high-efficiency thermal management in server cooling and industrial enclosures.
For engineers reviewing the A4949GLJTR-T datasheet, A4949GLJTR-T pinout, A4949GLJTR-T application, or A4949GLJTR-T equivalent, this page delivers verified package mapping (8-pin SOICN with exposed thermal pad), confirmed functional parameters (PWM input threshold 10% typ, IOCL = 1.6 A typ), protection behavior (TSD at 165°C), and real-world design context for fan control system integration.
Technical Context
The A4949GLJTR-T implements a proprietary sensorless sinusoidal drive algorithm that dynamically adapts motor current waveforms to minimize audible noise and vibration. It uses BEMF detection on phase A with a 300 mV hysteresis window during startup and operation, switching automatically from trapezoidal to sinusoidal mode as rotor speed increases.
Speed demand is derived from a 9-bit resolution PWM duty cycle measurement (10%–100% valid range, 0.1–100 kHz input frequency), converted internally to modulate three-phase outputs with 120° phase offset. The FG open-drain output provides one pulse per electrical revolution for closed-loop speed monitoring.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Motor PWM Frequency | 30 kHz typical - enables high-frequency switching to reduce audible noise and EMI in fan applications. |
| Speed Input Type | PWM (duty cycle) - supports 0.1–100 kHz input with 10% ON threshold and 7.5% OFF threshold for robust noise immunity. |
| Total Driver RDS(on) | 1.1 Ω typical at 12 V, 25°C - determines conduction loss and thermal rise under 1 A load conditions. |
| Overcurrent Limit (OCL) | 1.6 A typical - triggers cycle-by-cycle current limiting to protect MOSFETs and motor windings during stall or overload. |
| Thermal Shutdown (TSD) | 165°C typical with 20°C hysteresis - disables output until junction cools to ~145°C, preventing permanent damage. |
| Supply Voltage Range | 4–18 V - supports wide-input legacy and modern 12 V fan systems, including brownout resilience down to 4 V. |
| FG Output | Open-drain, 10 mA sink capability - provides scalable speed feedback signal compatible with microcontroller GPIO or comparator inputs. |
Pinout & Package
Package: 8-pin SOICN with exposed thermal pad (LJ package), RoHS-compliant, 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 return path for logic, gate drive, and thermal pad connection - must be tied to large copper pour for thermal dissipation. |
| 2 OUTA | Motor phase A output | High-side/low-side half-bridge output driving BLDC motor winding A - connects directly to motor terminal. |
| 3 VBB | Power supply input | 4–18 V main supply for internal regulators and gate drivers - requires CVBB capacitor (4.7–47 µF) near pin. |
| 4 PWM | Speed demand input | PWM duty cycle interface (0.1–100 kHz); internal 100 kΩ pulldown ensures safe-off state if disconnected. |
| 5 VREF | Analog reference output | 3.3 V ±3% regulated output - used for external circuit biasing or as ADC reference; requires 0.1 µF X5R ceramic decoupling. |
| 6 FG | Speed feedback output | Open-drain pulse output (1 pulse/electrical revolution); requires external pullup (e.g., 20 kΩ to VBB) for logic-level signaling. |
| 7 OUTC | Motor phase C output | High-side/low-side half-bridge output driving BLDC motor winding C - symmetrical with OUTA/OUTB for 3-phase commutation. |
| 8 OUTB | Motor phase B output | High-side/low-side half-bridge output driving BLDC motor winding B - completes 3-phase drive topology with 120° phase shift. |
| PAD | Exposed thermal pad | Internally connected to GND - must be soldered to PCB ground plane with ≥4 thermal vias for effective heat transfer and RθJA optimization. |
Key Features
| Feature | Design Value |
|---|---|
| 180° sinusoidal drive | Reduces torque ripple and acoustic noise by generating smooth current waveforms without position sensors. |
| Sensorless BEMF detection | Enables rotor position estimation using back-EMF on phase A - eliminates Hall sensors and associated PCB routing complexity. |
| Soft-start ramp control | Gradually increases speed demand and current limit over ~1.6 s (slow ramp) to limit inrush current and prevent mechanical shock. |
| Integrated lock protection | Disables outputs for 8 s upon stalled-rotor detection (via FG timeout), then attempts auto-restart - prevents thermal runaway. |
| Short-circuit & overcurrent protection | Monitors high-side current and disables source drivers mid-PWM cycle when IOCL (1.6 A typ) is exceeded - protects MOSFETs and motor. |
Applications
| Server Rack Cooling Fans | Industrial Enclosure Ventilation |
|---|---|
|
Use Scenario: High-density 1U/2U server racks requiring silent, reliable airflow with dynamic thermal response. IC Role / Device Role / Timing Role: Three-phase BLDC fan controller managing speed via PWM command from BMC/IPMI, with FG feedback for health monitoring. Use Value: Sinusoidal drive cuts audible noise by >15 dB(A) vs. trapezoidal drivers, while 30 kHz PWM frequency avoids resonant frequencies in metal chassis. |
Use Scenario: Fan-cooled PLC cabinets and HMI enclosures operating continuously in dusty, high-temperature factory environments. IC Role / Device Role / Timing Role: Standalone fan driver receiving PWM speed setpoint from industrial MCU, delivering robust motor control across –40°C to 105°C ambient. Use Value: Integrated lock detection and 8 s auto-restart ensure uninterrupted cooling during dust-clogged or bearing-failure events without manual intervention. |
| Telecom Base Station Heat Sinks | Medical Imaging Equipment Cooling |
|
Use Scenario: Forced-air cooling of RF power amplifiers and baseband processing units in outdoor telecom cabinets. IC Role / Device Role / Timing Role: Fan controller interfacing with thermal sensor network via PWM bus, providing precise speed modulation to maintain component junction temperatures. Use Value: Wide 4–18 V supply range allows direct use of telecom -48 V DC/DC converter outputs (with appropriate regulation), simplifying power architecture. |
Use Scenario: Low-vibration cooling for MRI gradient coil housings and CT detector modules where mechanical resonance affects image fidelity. IC Role / Device Role / Timing Role: Sensorless sinusoidal driver eliminating EMI from Hall sensors near sensitive analog front-ends, with FG output feeding diagnostic firmware. Use Value: 180° sinusoidal current waveform reduces torque ripple-induced vibrations below 0.5 µm peak-to-peak - critical for motion artifact suppression. |
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 |
|---|---|---|---|
| A4945GLJTR-T | Analog (VSP) speed input instead of PWM; identical pinout, package, and protection features; same 30 kHz motor PWM frequency and RDS(on). | Requires external DAC or potentiometer for speed control - suitable for analog-centric legacy systems lacking PWM generation capability. | Select A4945GLJTR-T only if analog voltage interface is mandated; note it was discontinued September 2024 and not recommended for new designs. |
| A5947KLPTR-T | Higher temperature grade (–40°C to 125°C), enhanced thermal performance (RθJA = 52°C/W), and updated startup algorithm - replaces discontinued K-variant A4949KLJTR-T parts. | Targeted for extended-temperature industrial and automotive under-hood applications where ambient exceeds 105°C. | Choose A5947KLPTR-T for new designs requiring >105°C operation or improved thermal headroom; not drop-in compatible due to different pinout and package (QFN). |
Compared with A4949GLJTR-T, A4945GLJTR-T offers analog speed control but is obsolete, while A5947KLPTR-T provides extended temperature capability and better thermal metrics at the cost of non-pin-compatible QFN packaging and revised layout requirements.
Availability
A4949GLJTR-T is available at Aetrix Electronics and suitable for server rack cooling, industrial enclosure ventilation, telecom base station heat sinks, and medical imaging equipment cooling requiring stable component supply, full traceability, and long-term lifecycle support.
Supply support for A4949GLJTR-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, power ICs, and motor driver solutions for automotive, industrial, and consumer markets.
The A4949GLJTR-T belongs to Allegro's three-phase sensorless fan driver product line, engineered specifically to replace noisy, inefficient brushed fans and trapezoidal BLDC drivers in thermally demanding, acoustically sensitive applications.
FAQ
What is the function of the PWM pin on the A4949GLJTR-T?
The PWM pin on the A4949GLJTR-T accepts a duty-cycle-modulated logic signal (0.1–100 kHz) to set fan speed. With a 10% typical ON threshold and 7.5% OFF threshold, it converts the measured duty cycle into a 9-bit speed demand value. An internal 100 kΩ pulldown resistor ensures the A4949GLJTR-T remains disabled if the PWM signal is disconnected, enhancing system safety during cable faults or connector unseating.
Does the A4949GLJTR-T require external position sensors?
No, the A4949GLJTR-T operates sensorlessly using back-EMF (BEMF) detection on the OUTA phase to estimate rotor position. It opens a narrow BEMF sampling window during the off-time of phase A, with 300 mV hysteresis to reject noise. This eliminates Hall-effect sensors or encoders, reducing bill-of-materials cost and PCB space while maintaining reliable startup and steady-state commutation for A4949GLJTR-T.
How does thermal management work on the A4949GLJTR-T?
The A4949GLJTR-T uses an exposed thermal pad (LJ package) electrically tied to GND and thermally coupled to PCB ground planes via ≥4 thermal vias. Its RθJA is specified at 62°C/W on a 2-layer board with 0.8 in² copper per side. Internal thermal shutdown activates at 165°C (typical), disabling outputs until junction temperature falls by 20°C - a safeguard explicitly defined in the A4949GLJTR-T datasheet for sustained reliability.
What protection features are built into the A4949GLJTR-T?
The A4949GLJTR-T integrates lock detection (8 s disable + auto-restart), overcurrent limiting (1.6 A typical), short-circuit protection, supply undervoltage lockout (3.91 V rising threshold), and thermal shutdown (165°C). Each feature acts autonomously: OCL disables source drivers mid-cycle; lock detection monitors FG timeout; UVLO holds the device in reset below threshold - all verified in the A4949GLJTR-T electrical characteristics table and functional description.
Can the A4949GLJTR-T drive fans at supply voltages below 12 V?
Yes, the A4949GLJTR-T supports 4–18 V supply operation. At 4 V, RDS(on) rises to 1.5 Ω (typ), increasing conduction loss but maintaining functionality. The 30 kHz motor PWM frequency and sinusoidal algorithm remain active, enabling low-speed, low-noise operation ideal for energy-efficient thermal throttling. This 4 V minimum is explicitly tested and guaranteed in the A4949GLJTR-T absolute maximum ratings and electrical characteristics sections.
A4949GLJTR-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:
- Active
- Motor Type - Stepper:
- Multiphase
- Motor Type - AC, DC:
- Brushless DC (BLDC)
- Function:
- Fan Control
- Output Configuration:
- Half Bridge (3)
- Interface:
- PWM
- 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
A4949GLJTR-T FAQ
1.How can I place an order for A4949GLJTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A4949GLJTR-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 A4949GLJTR-T reliable?
The price and inventory of A4949GLJTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A4949GLJTR-T is usually 5 days.
3.What payment methods are accepted for A4949GLJTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A4949GLJTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A4949GLJTR-T?
A4949GLJTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A4949GLJTR-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 A4949GLJTR-T?
For technical support, including A4949GLJTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A4949GLJTR-T requirements.
6.How does Aetrix verify that A4949GLJTR-T is sourced from the original manufacturer or authorized distributors?
All A4949GLJTR-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 A4949GLJTR-T meets industry standards.
7.What is the process for return or replacement of A4949GLJTR-T?
All A4949GLJTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A4949GLJTR-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 A4949GLJTR-T part is unused and in its original packaging.
Return procedure for A4949GLJTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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