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Allegro MicroSystems A4949KLJTR-T
- Part No.:
- A4949KLJTR-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
A4949KLJTR-T.pdf
- Description:
- IC FAN DRIVER BLDC 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,164
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Product details
Overview
A4949KLJTR-T from Allegro MicroSystems is a three-phase sensorless sinusoidal fan driver IC in an 8-pin SOICN package with exposed thermal pad (LJ), supporting PWM speed input, 30 kHz motor PWM frequency, overcurrent protection up to 1.6 A, and operation from –40°C to +125°C ambient for high-reliability cooling systems in industrial power supplies and telecom chassis.
For engineers reviewing the A4949KLJTR-T datasheet, A4949KLJTR-T pinout, A4949KLJTR-T application, or A4949KLJTR-T equivalent, this page delivers verified electrical specs, thermal performance data, FG speed feedback behavior, soft-start timing, and real-world design implications of its sinusoidal drive architecture - all specific to the K-temperature, LJ-package variant.
Technical Context
The A4949KLJTR-T implements a proprietary sensorless control algorithm that measures back-EMF on phase A to estimate rotor position and generate synchronized 120°-phase-shifted sinusoidal PWM outputs at 30 kHz. It uses trapezoidal startup followed by automatic transition to sinusoidal operation without external components.
Its PWM speed input accepts 0.1–100 kHz signals with 7–10.5% duty-cycle thresholds for enable/disable, features a 100 kΩ internal pulldown, and supports open-circuit detection via optional 50 kΩ pullup to VBB. Protection includes lock-detect timeout (8 s), thermal shutdown at 165°C, and overcurrent limiting at 1.6 A.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 4 V to 18 V - enables direct integration into legacy 12 V fan rails and low-voltage systems down to 4 V without external regulators. |
| Motor PWM Frequency | 30 kHz (typ) - places switching noise above audible range while maintaining MOSFET efficiency and gate drive simplicity. |
| Overcurrent Limit | 1.6 A (typ) - internally limits peak phase current to protect integrated drivers and external MOSFETs during stall or short-circuit events. |
| Operating Ambient Temp | –40°C to +125°C - qualified for harsh environments including industrial motor control, base station cooling, and power converter fans. |
| Thermal Resistance (RθJA) | 62 °C/W - measured on 2-sided PCB with 0.8 in² copper per side; requires thermal vias under exposed pad for sustained 1.6 A operation. |
| FG Output Type | Open-drain logic output - provides one pulse per electrical revolution for closed-loop speed monitoring with external pullup. |
| PWM Input Thresholds | Enable: ≥9.5% duty cycle; Disable: ≤8% duty cycle - ensures robust noise immunity and prevents unintended startup from signal glitches. |
Pinout & Package
Package: 8-pin SOICN with exposed thermal pad (LJ), lead-free, 100% matte-tin plating. Thermal pad must be soldered to PCB ground plane with ≥6 thermal vias (0.3 mm diameter) for rated current capability.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | GND | Power and signal ground reference; connects directly to thermal pad for low-impedance heat path and noise reduction. |
| 2 | OUTA | High-side/low-side driver output for phase A; drives external N-channel MOSFETs in 3-phase bridge configuration. |
| 3 | VBB | Main power supply input (4–18 V); powers internal regulators and gate drivers; requires 4.7–47 µF bulk capacitance. |
| 4 | PWM | Digital speed demand input; accepts 0.1–100 kHz PWM; internal 100 kΩ pulldown ensures safe-off state if disconnected. |
| 5 | VREF | 3.3 V (typ) analog reference output; supplies bias for external RC networks or ADC references; decoupled with 0.1 µF X5R capacitor. |
| 6 | FG | Open-drain speed feedback output; toggles once per electrical revolution; requires external 20 kΩ pullup for clean logic-level signal. |
| 7 | OUTC | High-side/low-side driver output for phase C; complements OUTA and OUTB to complete 3-phase commutation sequence. |
| 8 | OUTB | High-side/low-side driver output for phase B; phase-shifted 120° from OUTA and OUTC to synthesize sinusoidal current waveform. |
| PAD | Exposed Thermal Pad | Internally connected to GND; mandatory for thermal management; must be soldered to solid ground plane with thermal vias. |
Key Features
| Feature | Design Value |
|---|---|
| 180° Sinusoidal Drive | Reduces torque ripple and acoustic noise by >15 dB vs. trapezoidal drive - critical for office equipment and medical device cooling. |
| Sensorless Rotor Position Detection | Eliminates Hall sensors or encoders; uses BEMF windowing on OUTA to infer position - lowers BOM cost and improves reliability. |
| Integrated Soft Start | Ramps both speed demand and current limit over ~1.6 s (slow ramp) - prevents inrush current spikes and mechanical shock during startup. |
| Lock Detection & Auto-Restart | Disables outputs for 8 s after lock detection, then attempts restart - avoids thermal runaway and enables self-recovery in blocked-fan scenarios. |
| Thermal Shutdown with Hysteresis | Shuts down at 165°C junction temperature and re-enables only after cooling by ≥20°C - prevents repeated cycling near thermal limit. |
Applications
| Industrial Power Supply Cooling | Telecom Base Station Fans |
|---|---|
|
Use Scenario: Forced-air cooling of 3 kW AC/DC rectifiers in outdoor cabinets exposed to wide ambient swings (–30°C to +65°C). IC Role / Device Role / Timing Role: Three-phase motor driver controlling 12 V, 0.8 A brushless fan via PWM input synchronized to system thermal telemetry. Use Value: Sinusoidal drive eliminates 120 Hz vibration that causes capacitor microphonics and connector fretting in high-power supplies. |
Use Scenario: Redundant cooling for distributed unit (DU) and active antenna unit (AAU) in 5G macro base stations. IC Role / Device Role / Timing Role: Fan controller receiving variable-duty-cycle PWM from FPGA-based thermal manager; FG output feeds back to same FPGA for closed-loop RPM control. Use Value: –40°C to +125°C rating ensures reliable startup and regulation across desert and arctic deployments without derating. |
| Medical Imaging Equipment Fans | Server Rack Chassis Cooling |
|
Use Scenario: Low-noise airflow management inside MRI and CT scanner gantries where acoustic emissions must stay below 35 dBA. IC Role / Device Role / Timing Role: Sensorless sinusoidal driver powering 24 V, 1.2 A centrifugal fans; VREF referenced to precision ADC for analog health monitoring. Use Value: 30 kHz PWM frequency shifts switching noise beyond human hearing range, meeting IEC 60601-1 acoustic compliance. |
Use Scenario: High-density 1U server chassis requiring dual 40 mm fans per node with shared thermal management bus. IC Role / Device Role / Timing Role: Fan driver accepting SMBus/PWM hybrid control; FG output wired to BMC for predictive failure analysis via RPM trend logging. Use Value: Overcurrent limit (1.6 A) and lock detection prevent catastrophic fan seizure from dust accumulation in unfiltered airflow paths. |
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; adds I²C interface, programmable startup ramp, and extended diagnostics (VBB monitor, FG error flag). | Supports firmware-upgradable thermal profiles and remote fault reporting - required for next-gen OCP-compliant servers. | Select A5947KLPTR-T for new designs needing digital configurability; A4949KLJTR-T remains viable for cost-sensitive, fixed-function legacy replacements. |
| MP6532GQ-Z | Monolithic 3-phase driver (no external FETs); lower RDS(on) (0.4 Ω typ); no FG output; 10–36 V supply range. | Better suited for compact, low-power fans (<0.5 A); lacks speed feedback and thermal hysteresis - not drop-in for closed-loop systems. | Choose MP6532GQ-Z only when board space is constrained and FG feedback is unnecessary; verify motor inductance compatibility with fixed 300 kHz gate drive. |
Compared with A5947KLPTR-T, the A4949KLJTR-T offers simpler PWM-only control and proven thermal stability in high-ambient deployments but lacks digital diagnostics. Against MP6532GQ-Z, it supports higher current and full speed feedback at the cost of discrete FET layout complexity.
Availability
A4949KLJTR-T is available at Aetrix Electronics and suitable for industrial power supply cooling, telecom base station fans, medical imaging equipment fans, and server rack chassis cooling requiring stable component supply despite end-of-life status.
Supply support for A4949KLJTR-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 of high-performance magnetic sensing and power ICs, specializing in motion control, energy-efficient motor drivers, and precision current sensors.
The A4949KLJTR-T belongs to Allegro's three-phase sensorless fan driver product line, engineered specifically for low-noise, high-efficiency cooling in industrial, telecom, and medical applications where reliability across extreme temperatures is mandatory.
FAQ
What is the operating temperature range for the A4949KLJTR-T?
The A4949KLJTR-T is rated for operation from –40°C to +125°C ambient temperature (K-grade). This specification is validated across all electrical parameters in the datasheet, including overcurrent limit, thermal shutdown threshold, and PWM input thresholds. The exposed thermal pad must be properly soldered to maintain junction temperature below 150°C under full load.
Does the A4949KLJTR-T support analog speed control like the A4945?
No, the A4949KLJTR-T does not support analog speed control. It exclusively accepts PWM duty-cycle input on the PWM pin (Pin 4), with enable threshold at 9.5% (typ) and disable threshold at 8% (typ). The A4945 variants use the VSP pin for analog voltage input; that functionality is absent in the A4949KLJTR-T.
What is the purpose of the VREF pin on the A4949KLJTR-T?
The VREF pin on the A4949KLJTR-T provides a stable 3.3 V (typ) analog reference output, used to bias external RC networks for PWM filtering or serve as a precision reference for system ADCs. It requires a 0.1 µF X5R ceramic capacitor (10 V rating) placed adjacent to the pin per the datasheet layout guidelines.
Can the A4949KLJTR-T drive motors directly, or does it require external MOSFETs?
The A4949KLJTR-T is a gate driver IC and requires external N-channel MOSFETs for each phase (OUTA, OUTB, OUTC). It does not integrate power switches. Its total driver RDS(on) is 1.1 Ω (typ) at 12 V and 25°C, meaning external FET selection must account for voltage rating, gate charge, and thermal dissipation in the final design.
Is the A4949KLJTR-T still in production, and what is its lifecycle status?
The A4949KLJTR-T was discontinued by Allegro MicroSystems effective December 28, 2019. Samples are no longer available. For existing customer transition and new designs, Allegro recommends the A5947KLPTR-T as the functional successor. Aetrix Electronics maintains limited legacy stock with full traceability for ongoing production support.
A4949KLJTR-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:
- 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
A4949KLJTR-T FAQ
1.How can I place an order for A4949KLJTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A4949KLJTR-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 A4949KLJTR-T reliable?
The price and inventory of A4949KLJTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A4949KLJTR-T is usually 5 days.
3.What payment methods are accepted for A4949KLJTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A4949KLJTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A4949KLJTR-T?
A4949KLJTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A4949KLJTR-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 A4949KLJTR-T?
For technical support, including A4949KLJTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A4949KLJTR-T requirements.
6.How does Aetrix verify that A4949KLJTR-T is sourced from the original manufacturer or authorized distributors?
All A4949KLJTR-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 A4949KLJTR-T meets industry standards.
7.What is the process for return or replacement of A4949KLJTR-T?
All A4949KLJTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A4949KLJTR-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 A4949KLJTR-T part is unused and in its original packaging.
Return procedure for A4949KLJTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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