My Inquiry
My Account
Allegro MicroSystems A4945GLTR-T
- Part No.:
- A4945GLTR-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- -
- Datasheet:
-
A4945GLTR-T.pdf
- Description:
- IC FAN DRIVER BLDC SOT89-3
- Quantity:
- Payment:
- Shipping:
Inventory:3,886
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
A4945GLTR-T from Allegro MicroSystems is a three-phase sensorless sinusoidal fan driver IC designed for medium-power brushless DC (BLDC) fans. It delivers 180° sinusoidal drive, supports analog speed control via VSP pin (0.45–3.05 V), provides FG speed feedback output, and integrates overcurrent protection (1.6 A typ), thermal shutdown (165°C), and soft-start functionality - enabling low-noise, high-efficiency cooling in server and telecom chassis applications.
For engineers reviewing the A4945GLTR-T datasheet, A4945GLTR-T pinout, A4945GLTR-T application, or A4945GLTR-T equivalent, key selection considerations include its 8-pin SOICN package without exposed thermal pad, analog speed input interface, –40°C to 105°C operating range, and discontinued status requiring legacy design support or transition planning.
Technical Context
The A4945GLTR-T implements a proprietary sensorless commutation algorithm that dynamically adapts sinusoidal current waveforms to motor back-EMF characteristics across speeds from startup to full operation. Its trapezoidal startup phase transitions automatically to sinusoidal drive without external components.
Speed demand is converted from analog voltage on the VSP pin into a 9-bit value driving an internal PWM generator with 30 kHz (28–32 kHz) motor output frequency and 120° phase-shifted outputs (OUTA/OUTB/OUTC). BEMF detection occurs within a narrow window on phase A to minimize waveform distortion while maintaining precise rotor position tracking.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 4 V to 18 V - supports wide-input legacy power rails and enables direct integration into 5 V, 12 V, or 15 V fan systems without external regulators. |
| Motor Output Frequency | 30 kHz (28–32 kHz) - high-frequency PWM minimizes audible noise and reduces EMI filtering requirements in fan subsystems. |
| VSP Analog Input Range | 0.45 V to 3.05 V - maps linearly to 7.5%–100% speed demand; below 228 mV disables motor, enabling safe low-speed cutoff. |
| Total RDS(on) | 1.1 Ω (typ) at 12 V - ensures low conduction loss and thermal rise during continuous 1 A motor load operation. |
| Overcurrent Limit | 1.6 A (typ) - internally limits peak phase current to protect MOSFETs and motor windings during stall or overload conditions. |
| Thermal Shutdown Threshold | 165°C (typ) - triggers automatic shutdown before junction temperature reaches 150°C max rating, preventing permanent damage. |
| FG Output Type | Open-drain logic output - provides one pulse per electrical revolution for tachometer feedback; compatible with 3.3 V or 5 V microcontroller inputs. |
Pinout & Package
Package: 8-pin SOICN (L package), lead-free with 100% matte-tin plating; no exposed thermal pad - suitable for wave soldering but requires PCB copper area and thermal vias only if used near thermal limits.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | GND | Power and signal ground reference; must be connected to low-impedance PCB ground plane to ensure stable VREF and accurate BEMF sensing. |
| 2 | OUTA | High-side/low-side gate driver output for phase A; connects directly to motor winding terminal A. |
| 3 | VBB | Main power supply input (4–18 V); decoupled by CVBB capacitor (4.7–47 µF) placed adjacent to pin for transient suppression. |
| 4 | VSP | Analog speed demand input (0–3.05 V); internal 100 kΩ pulldown ensures motor disable on open-circuit condition. |
| 5 | VREF | Stable 3.3 V (3.2–3.4 V) analog reference output; powers external circuitry or serves as ADC reference; requires 0.1 µF X5R ceramic bypass. |
| 6 | FG | Open-drain tachometer output; pulses once per electrical revolution; requires external pullup resistor (e.g., 20 kΩ to 5 V). |
| 7 | OUTC | High-side/low-side gate driver output for phase C; connects directly to motor winding terminal C. |
| 8 | OUTB | High-side/low-side gate driver output for phase B; connects directly to motor winding terminal B. |
Key Features
| Feature | Design Value |
|---|---|
| 180° sinusoidal drive | Reduces torque ripple and acoustic noise by >15 dB compared to trapezoidal drive, critical for datacenter and office environment fan applications. |
| Sensorless BEMF position detection | Eliminates Hall-effect sensors or encoder interfaces, reducing bill-of-materials cost and board space by ~30% in BLDC fan modules. |
| Integrated soft start | Ramps current limit and speed demand simultaneously to limit inrush current to ≤50 mA steps every 128 ms, avoiding power rail sag in multi-fan systems. |
| Lock detection with auto-restart | Disables outputs for 8 s (7–9 s) upon rotor lock detection, then attempts restart - prevents thermal runaway during fan obstruction events. |
| Supply undervoltage lockout (UVLO) | Enables operation only above 3.85 V and disables below 3.5 V (3.85 V – 0.3 V hysteresis), ensuring reliable startup and preventing erratic behavior at brownout. |
Applications
| Server Chassis Cooling | Telecom Power Shelf Fans |
|---|---|
|
Use Scenario: High-density 1U/2U servers requiring quiet, reliable airflow across ASICs and memory modules under variable thermal loads. IC Role / Device Role / Timing Role: Three-phase BLDC fan controller managing up to 15 W motor loads with closed-loop speed regulation via FG feedback. Use Value: Sinusoidal drive cuts audible noise by ≥12 dB(A) vs. square-wave drivers, meeting ASHRAE TC 90.1 acoustic compliance for enterprise data centers. |
Use Scenario: Forced-air cooling of rectifier modules and DC-DC converters in -48 V telecom power shelves operating continuously at 60°C ambient. IC Role / Device Role / Timing Role: Sensorless motor driver delivering stable 3,000–12,000 RPM control across 4–18 V input range with thermal foldback at 105°C. Use Value: Integrated OCL (1.6 A) and TSD (165°C) prevent field failures due to dust-clogged fans or blocked vents without external protection circuitry. |
| Industrial PC Ventilation | Medical Imaging Equipment Fans |
|
Use Scenario: Fan-cooled embedded controllers in factory automation cabinets exposed to vibration, dust, and 0–105°C ambient swings. IC Role / Device Role / Timing Role: Analog-controlled fan driver accepting 0–3.3 V speed command from PLC I/O or temperature sensor DAC output. Use Value: VSP input linearity (±6 LSB) and 9-bit resolution enable precise 1% speed granularity across full 7.5–100% range for thermal management algorithms. |
Use Scenario: Low-noise cooling for MRI gradient amplifier cabinets where EMI and acoustic interference must be minimized near sensitive RF receivers. IC Role / Device Role / Timing Role: EMI-optimized 30 kHz motor drive IC with filtered VSP input and clean FG tach output synchronized to motor electrical cycles. Use Value: 30 kHz PWM frequency places switching harmonics beyond 100 kHz, easing compliance with IEC 60601-1-2 Class B conducted emissions limits. |
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 extended –40°C to 125°C K-grade rating, integrated 5 V LDO, and enhanced lock-detection algorithm; uses 10-pin MLP package. | Supports higher ambient environments (e.g., outdoor base stations); requires PCB redesign due to different pin count and exposed pad layout. | Select when new designs require extended temperature range or improved thermal robustness; not pin-compatible with A4945GLTR-T. |
| A4949GLTR-T | PWM-speed-input variant (not analog); identical pinout, package, and protection features; same 8-pin SOICN L package and 30 kHz output frequency. | Requires PWM signal source instead of analog voltage; shares same thermal performance and FG feedback capability. | Choose for systems already using PWM-based speed control infrastructure; retains identical board layout but changes interface logic. |
Compared with A4945GLTR-T, A5947KLPTR-T offers broader temperature support and integrated regulation but demands layout revision, while A4949GLTR-T preserves mechanical compatibility and thermal behavior but replaces analog speed control with PWM - making it the only drop-in functional alternative for existing SOICN footprints.
Availability
A4945GLTR-T is available at Aetrix Electronics and suitable for legacy server chassis cooling, telecom power shelf ventilation, and industrial PC thermal management requiring stable component supply despite end-of-life status.
Supply support for A4945GLTR-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 IC solutions, specializing in motion control, energy-efficient motor drivers, and precision current sensing.
The A4945 family was developed specifically for cost-sensitive, low-noise BLDC fan applications in computing and communications infrastructure, emphasizing analog speed control, sensorless operation, and integrated protection.
FAQ
Is A4945GLTR-T still in production?
No, A4945GLTR-T has been discontinued as of September 30, 2024. Allegro MicroSystems confirms this variant is no longer in production, samples are unavailable, and it should not be selected for new designs. Aetrix Electronics maintains limited legacy stock for ongoing maintenance and repair of deployed systems, with full traceability and documentation for each batch of A4945GLTR-T.
What is the difference between A4945GLTR-T and A4945GLJTR-T?
A4945GLTR-T uses the standard 8-pin SOICN (L) package without an exposed thermal pad, while A4945GLJTR-T uses the 8-pin SOICN with exposed thermal pad (LJ) package. Both share identical electrical specifications, pinout, and analog speed input functionality, but the LJ variant offers lower thermal resistance (62°C/W vs. 140°C/W) for higher-power or higher-ambient deployments. Both variants were discontinued simultaneously on September 30, 2024.
Can A4945GLTR-T be replaced with A4949GLTR-T on the same PCB?
Yes, A4945GLTR-T and A4949GLTR-T share identical 8-pin SOICN (L) packaging, pinout, and thermal characteristics - making them mechanically interchangeable. However, A4949GLTR-T accepts PWM speed commands on pin 4 instead of analog voltage, so firmware or upstream control circuitry must be modified to generate a 10–100 kHz PWM signal with 10–100% duty cycle. The A4949GLTR-T remains active in production as a functional alternative to A4945GLTR-T.
What is the purpose of the VREF pin on A4945GLTR-T?
The VREF pin on A4945GLTR-T provides a stable 3.3 V (3.2–3.4 V) analog reference output, internally regulated and buffered. It serves dual purposes: powering external circuitry such as temperature sensor signal conditioning, and acting as a precision reference for ADCs measuring fan speed or system temperature. A 0.1 µF X5R ceramic capacitor must be placed directly between VREF and GND to maintain stability and noise immunity for A4945GLTR-T operation.
Does A4945GLTR-T support closed-loop speed control?
A4945GLTR-T supports basic closed-loop speed regulation via its FG (tachometer) output, which delivers one open-drain pulse per electrical revolution - enabling microcontrollers to measure actual RPM and adjust the VSP analog input voltage accordingly. While A4945GLTR-T itself does not implement PID or digital loop compensation, its FG feedback path and linear VSP response (±6 LSB accuracy) provide the essential hardware foundation for external closed-loop control algorithms in host systems.
A4945GLTR-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- -
- 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 ~ 105°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
A4945GLTR-T FAQ
1.How can I place an order for A4945GLTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A4945GLTR-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 A4945GLTR-T reliable?
The price and inventory of A4945GLTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A4945GLTR-T is usually 5 days.
3.What payment methods are accepted for A4945GLTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A4945GLTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A4945GLTR-T?
A4945GLTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A4945GLTR-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 A4945GLTR-T?
For technical support, including A4945GLTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A4945GLTR-T requirements.
6.How does Aetrix verify that A4945GLTR-T is sourced from the original manufacturer or authorized distributors?
All A4945GLTR-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 A4945GLTR-T meets industry standards.
7.What is the process for return or replacement of A4945GLTR-T?
All A4945GLTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A4945GLTR-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 A4945GLTR-T part is unused and in its original packaging.
Return procedure for A4945GLTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
A4945GLTR-T Tags
-
DRV2603RUNR
Texas Instruments
-
DRV8837CDSGR
Texas Instruments
-
DRV8837DSGR
Texas Instruments
-
DRV8838DSGR
Texas Instruments
-
DRV8839DSSR
Texas Instruments
-
EMC2301-1-ACZL-TR
Microchip Technology
-
DRV8231ADSGR
Texas Instruments
-
EMC2302-2-AIZL-TR
Microchip Technology
-
DRV8800PWPR
Texas Instruments
-
DRV8835DSSR
Texas Instruments
-
EMC2303-1-KP-TR
Microchip Technology
-
DRV8876PWPR
Texas Instruments
Tech Hub
A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.
TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
