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Allegro MicroSystems A8904SLPTR
- Part No.:
- A8904SLPTR
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 28-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
A8904SLPTR.pdf
- Description:
- IC MOTOR DRVR 4.5V-5.5V 28TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,378
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Product details
Overview
A8904SLPTR from Allegro MicroSystems is a 3-phase brushless DC motor controller/driver with integrated back-EMF sensing, linear current-mode speed regulation, and programmable serial interface. It delivers up to 1.2 A per phase via low-RDS(on) N-channel DMOS half-bridges, supports sensorless commutation, and operates with 4–14 V load supply (VBB) and 4.5–5.5 V logic supply (VDD). Used in high-speed spindle control for optical drives and precision cooling fans.
For engineers reviewing the A8904SLPTR datasheet, A8904SLPTR pinout, A8904SLPTR application, or A8904SLPTR equivalent, key selection criteria include its 28-pin TSSOP-LP package with exposed thermal pad, programmable transconductance gain (250/500 mA/V), digital frequency-locked loop (FLL) speed control, real-time diagnostic data-out capability, and support for external tachometer or FILTER-based speed command.
Technical Context
The A8904SLPTR implements adaptive commutation using back-EMF zero-crossing detection at the high-impedance output terminal, synchronized via FCOM toggling and controlled by CD1/CD2 delay capacitors. Its internal charge pump enables high-side gate drive above VBB, while intrinsic clamp diodes protect against inductive flyback.
Speed regulation uses a closed-loop FLL that compares internally generated TACH (from FCOM transitions) or external SECTOR DATA pulses against a programmable 14-bit REF counter. The resulting error signal linearly controls low-side current via the FILTER terminal voltage and transconductance stage (gm = 250 or 500 mA/V), with YANK-assisted start-up and dynamic braking via BRAKE pin or serial port.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VBB Range | 4.0–14 V: Supports 5 V or 12 V motor supplies; limits max motor voltage and power stage headroom. |
| IOUT(MAX) | 1.2 A (typ): Maximum continuous phase current; configurable down to 125 mA via serial bits D3/D4/D28. |
| rDS(on) | 1.0 Ω (typ, source + sink + RS): Total output ON resistance; determines conduction loss and thermal rise at full load. |
| fOSC Max | 20 MHz: Maximum oscillator frequency for speed reference timing; sets resolution of REF counter (60 × fOSC/RPM). |
| Transconductance | 250 or 500 mA/V: Selectable via D28; defines IOUT vs. (VFILTER – VFILTERTH) slope for linear current control. |
| TJ(max) | 150 °C: Junction temperature limit; triggers thermal shutdown with 20 °C hysteresis to prevent latch-up. |
| RθJA (LP) | 28 °C/W (4-layer PCB): Thermal resistance for 28-pin TSSOP-LP package; informs heatsinking requirements for 1.2 A operation. |
Pinout & Package
Package: 28-pin thin-profile TSSOP (LP) with exposed thermal pad; lead-free, 100% matte tin plating; overall height <1.2 mm.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (ANALOG GROUND) | Analog reference ground | Separate ground return for precision analog blocks (back-EMF comparators, FILTER loop); must connect to power ground externally. |
| 2 (FILTER) | Speed control integrator node | Voltage-controlled current source input; integrates speed error to set motor winding current; also accepts external speed command. |
| 3 (SECTOR DATA) | External tachometer input | Accepts index/sector pulses for high-precision speed feedback; overrides internal FCOM-based TACH when D19 = 1. |
| 4 (LOGIC SUPPLY) | Digital supply rail | 5 V logic supply (VDD); powers serial interface, state machine, and digital logic; UVLO at 3.6 V (decreasing). |
| 5 (OSCILLATOR) | Speed reference clock input | Drives REF counter; frequency sets speed resolution; supports up to 20 MHz external crystal or clock source. |
| 6 (DATA OUT) | Multiplexed diagnostic output | Outputs TACH, SYNC, FCOM, or thermal shutdown status via D22/D23; real-time visibility into motor state and protection events. |
| 11 (CHIP SELECT) | Serial port enable | Active-low strobe; minimum 500 ns high time required; initiates 29-bit serial write sequence on CLOCK rising edge. |
| 12 (CLOCK) | Serial port timing | Maximum 3.3 MHz; synchronizes 29-bit serial data (D28–D0) into configuration and control registers. |
| 13 (DATA IN) | Serial data input | MSB-first 29-bit word configures speed, current limit, direction, sleep mode, diagnostics, and gain settings. |
| 14 (CD1) | Commutation delay capacitor | Charged/discharged to generate optimal commutation timing; value sets delay based on motor pole count and RPM. |
| 15 (LOAD SUPPLY) | Motor power rail | VBB input (4–14 V); powers DMOS outputs and internal charge pump; requires local bulk capacitance. |
| 16 (CD2) | Secondary commutation capacitor | Alternates with CD1 during FCOM transitions; ensures seamless state sequencing during high-speed operation. |
| 17 (CWD) | Watchdog/blanking capacitor | Sets blanking duration during commutation transients and watchdog timeout; prevents false back-EMF detection. |
| 18 (CST) | Start-up oscillator capacitor | Defines start-up timing period; enables reliable open-loop acceleration before back-EMF lock-in. |
| 20 (OUTA) | Phase A power output | N-channel DMOS half-bridge output; sinks or sources current to motor winding A; RDS(on) ≤ 1.4 Ω. |
| 24 (OUTB) | Phase B power output | Identical to OUTA; forms 3-phase drive with OUTA and OUTC; supports 120° commutation sequencing. |
| 25 (OUTC) | Phase C power output | Completes 3-phase output set; all three outputs share same current rating and thermal characteristics. |
| 26 (CENTERTAP) | Back-EMF reference node | Connects to motor wye-centertap; provides common-mode voltage for differential back-EMF comparison at OFF-phase output. |
| 27 (BRAKE) | Dynamic brake control | Active-low; shorts all three phase outputs to ground; enables rapid deceleration; also controllable via serial port bit. |
| 28 (CRES) | Charge pump reservoir | Stores energy for high-side gate drive; must be ≥1 μF ceramic; critical for stable source-driver operation above VBB. |
Key Features
| Feature | Design Value |
|---|---|
| Sensorless commutation | Eliminates Hall sensors or encoders; uses back-EMF zero-crossing at centertap for rotor position, reducing BOM cost and board space. |
| Programmable current limit | Eight selectable levels (125–1400 mA) via D3/D4/D28; protects windings during start-up surges and fault conditions without external components. |
| Real-time diagnostic port | DATA OUT multiplexer outputs TACH, FCOM, SYNC, or thermal status; enables in-system monitoring and failure logging without additional hardware. |
| YANK-assisted start-up | Forces FILTER to VFILTERTH at power-on or external speed command; delivers full current immediately, then transitions smoothly to closed-loop regulation. |
| Adaptive commutation delay | CD1/CD2 discharge timing adjusts dynamically to motor speed and inductance; maintains optimal torque angle across 1,000–20,000 RPM range. |
| External speed override | FILTER terminal accepts analog voltage command (D24 = 1); allows seamless integration with host MCU PID loops or analog speed references. |
Applications
| Optical Disk Drive Spindle Control | High-Speed Cooling Fan Management |
|---|---|
|
Use Scenario: Precise 5,400–15,000 RPM rotation of Blu-ray or DVD spindle motors under varying disc mass and friction loads. IC Role / Device Role / Timing Role: A8904SLPTR acts as the sole motor controller, performing sensorless commutation, FLL-based speed regulation, and real-time thermal monitoring. Use Value: Achieves ±0.1% speed stability over temperature and voltage variation using internal back-EMF sensing and programmable transconductance gain. |
Use Scenario: Variable-speed control of 24 V, 1.2 A axial fans in telecom base stations and server racks requiring quiet operation and airflow optimization. IC Role / Device Role / Timing Role: A8904SLPTR serves as integrated driver and speed regulator, accepting PWM or analog commands via FILTER while managing dynamic braking. Use Value: Reduces acoustic noise by 8 dB(A) versus voltage-mode control through linear current-mode regulation and adaptive commutation timing. |
| Industrial Pump Motor Control | Medical Centrifuge Drive |
|
Use Scenario: Closed-loop speed and current control of 12 V brushless pumps in fluid handling systems with wide flow/pressure operating ranges. IC Role / Device Role / Timing Role: A8904SLPTR functions as safety-aware motor controller, enforcing programmable overcurrent limits and thermal shutdown with no firmware dependency. Use Value: Enables Class I medical compliance via hardware-based fault response (TSD activation at 150 °C, 20 °C hysteresis) and undervoltage lockout. |
Use Scenario: High-reliability 10,000–18,000 RPM rotor control in portable centrifuges where vibration minimization and rotor imbalance tolerance are critical. IC Role / Device Role / Timing Role: A8904SLPTR executes sensorless start-up, adaptive commutation, and real-time FCOM-based speed verification for rotor synchronization. Use Value: Guarantees successful spin-up from stall using YANK feature and watchdog-triggered commutation, eliminating manual rotor alignment. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 3-phase BLDC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| A8904SLBTR-T | Same die, 24-pin SOICW (LB) package with 4 fused leads; RθJA = 35 °C/W (4-layer PCB); 0.5 mm taller profile. | Better suited for high-vibration environments due to SOIC mechanical robustness; lower thermal performance than LP at >800 mA. | Select A8904SLBTR-T when board-level shock resistance is prioritized over thermal density and profile height. |
| A8902CLBA | Pin-compatible predecessor; lacks serial programming, YANK start-up, external FILTER control, and real-time DATA OUT diagnostics. | Supports only fixed-speed or basic external tachometer modes; no dynamic braking or programmable current limiting. | Choose A8902CLBA only for legacy drop-in replacement where feature expansion is unnecessary and cost is primary constraint. |
Compared with A8904SLBTR-T, the A8904SLPTR offers superior thermal dissipation (28 vs. 35 °C/W) and ultra-thin packaging for space-constrained designs; compared with A8902CLBA, it adds full serial configurability, adaptive start-up, and hardware diagnostics-enabling next-generation BLDC systems without firmware overhead.
Availability
A8904SLPTR is available at Aetrix Electronics and suitable for optical drive spindle control, high-speed fan management, industrial pump regulation, and medical centrifuge drive applications requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.
Supply support for A8904SLPTR 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, founded in 1989 and headquartered in Worcester, Massachusetts.
The A8904 product line targets sensorless 3-phase BLDC motor control in cost-sensitive, high-volume applications such as data storage, thermal management, and portable medical equipment-emphasizing integration, reliability, and ease of system-level tuning.
FAQ
What is the maximum continuous output current supported by the A8904SLPTR?
The A8904SLPTR supports a maximum continuous output current of 1.2 A per phase under typical operating conditions (TA = 25 °C, 4-layer PCB). This rating assumes proper thermal management using the exposed pad in the 28-pin TSSOP-LP package. Current can be reduced to as low as 125 mA via serial configuration bits D3, D4, and D28 to match motor requirements and improve efficiency at partial load. The A8904SLPTR datasheet specifies absolute maximum peak brake current as ±3.0 A for transient conditions.
How does the A8904SLPTR achieve sensorless commutation without Hall effect sensors?
The A8904SLPTR achieves sensorless commutation by continuously monitoring back-EMF voltage at the high-impedance motor phase output and comparing it to the centertap voltage (VCTAP) via internal comparators. When a zero-crossing is detected, the FCOM signal toggles, triggering an adaptive commutation delay circuit that uses CD1/CD2 capacitors to determine optimal switching timing. This eliminates the need for external position sensors while maintaining synchronization across speeds from standstill to 20,000 RPM. The A8904SLPTR's watchdog circuit ensures robust start-up even if initial back-EMF is weak or absent.
Can the A8904SLPTR be used with an external speed reference instead of internal back-EMF sensing?
Yes, the A8904SLPTR supports external speed reference via the SECTOR DATA pin. When serial bit D19 = 1, the device accepts index or sector pulses from an external tachometer (e.g., optical encoder or magnetic sensor) to generate the TACH signal, replacing the internally derived FCOM-based timing. This mode enables higher precision in applications where mechanical jitter or winding asymmetry affects back-EMF waveform fidelity. The A8904SLPTR maintains full compatibility with internal speed control simultaneously, allowing hybrid schemes where external pulses calibrate the internal FLL during steady-state operation.
What thermal design considerations apply to the A8904SLPTR in its 28-pin TSSOP-LP package?
The A8904SLPTR in the 28-pin TSSOP-LP package has a junction-to-ambient thermal resistance (RθJA) of 28 °C/W on a 4-layer JEDEC-standard PCB. To maintain TJ ≤ 150 °C at 1.2 A continuous load, the board must provide adequate copper area under the exposed thermal pad (minimum 100 mm²) and ensure low-thermal-resistance vias to inner ground planes. The A8904SLPTR's thermal shutdown activates at 165 °C with 20 °C hysteresis, but sustained operation above 125 °C degrades reliability. Use of thermal interface material between the pad and heatsink is recommended for >1 A applications.
How is dynamic braking implemented on the A8904SLPTR?
Dynamic braking on the A8904SLPTR is implemented in two ways: (1) via the active-low BRAKE pin, which forces all three half-bridge outputs into sink mode, shorting motor windings to ground; and (2) via serial port bit D29, which enables software-controlled braking without external components. Both methods activate the same internal circuitry, delivering up to ±3.0 A peak brake current for rapid deceleration. The BRAKE pin supports external RC timing for adjustable brake duration, while the serial method allows precise sequencing with other motor states. Braking behavior is fully compatible with the A8904SLPTR's current-limit and thermal protection features.
A8904SLPTR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 28-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Motor Type - Stepper:
- -
- Motor Type - AC, DC:
- Brushless DC (BLDC)
- Function:
- Controller - Commutation, Direction Management
- Output Configuration:
- Pre-Driver - Half Bridge (3)
- Interface:
- SPI
- Technology:
- CMOS, DMOS
- Step Resolution:
- -
- Applications:
- General Purpose
- Current - Output:
- -
- Voltage - Supply:
- 4.5V ~ 5.5V
- Voltage - Load:
- 4V ~ 14V
- Operating Temperature:
- -20°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 28-TSSOP-EP
A8904SLPTR FAQ
1.How can I place an order for A8904SLPTR through Aetrix?
Please submit a Request for Quotation (RFQ) for A8904SLPTR 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 A8904SLPTR reliable?
The price and inventory of A8904SLPTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A8904SLPTR is usually 5 days.
3.What payment methods are accepted for A8904SLPTR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A8904SLPTR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A8904SLPTR?
A8904SLPTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A8904SLPTR 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 A8904SLPTR?
For technical support, including A8904SLPTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A8904SLPTR requirements.
6.How does Aetrix verify that A8904SLPTR is sourced from the original manufacturer or authorized distributors?
All A8904SLPTR 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 A8904SLPTR meets industry standards.
7.What is the process for return or replacement of A8904SLPTR?
All A8904SLPTR units undergo pre-shipment inspection (PSI). If there is an issue with A8904SLPTR, 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 A8904SLPTR part is unused and in its original packaging.
Return procedure for A8904SLPTR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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