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A8904 3-Phase Brushless DC Motor Controller/Driver with Back EMF Sensing

Discontinued Product
These parts are no longer in production The device should not be purchased for new design applications. Samples are no longer available.

Date of status change: November 1, 2010

Recommended Substitutions:

For existing customer transition, and for new customers or new applications, contactAllegro Sales.

NOTE: For detailed information on purchasing options, contact your local Allegro field applications engineer or sales representative.

Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand.The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.

A8904 3-Phase Brushless DC Motor Controller/Driver with Back EMF Sensing
Features and Benefits
▪ Pin-for-pin replacement for A8902CLBA ▪ Start-upcommutation circuitry ▪ Sensorless commutation circuitry ▪ Option of external sector data tachometer signal ▪ Option of external speed control ▪ Oscillator operation up to 20 MHz ▪ Programmable overcurrent limit ▪ Transconductance gain options: 500 mA/V or 250 mA/V ▪ Programmable watchdog timer ▪ Directional control ▪ Serial port interface ▪ TTL-compatible inputs ▪ System diagnostics data-outported in real time ▪ Dynamic braking through serial port or external terminal

Description
The A8904 is a 3-phase brushless DC motor controller/driver designed for applications where accurate control of high-speed motors is required. The three half-bridge outputs are low on-resistance, N-channel DMOS devices capable of driving up to 1.2 A. The A8904 provides complete, reliable, self-contained backEMF sensing, motor start-up, and running algorithms. A programmable digital frequency-locked loop speed control circuit together with the linear current control circuitry provides precise motor speed regulation. A serial port allows the user to program various features and modes of operation, such as the speed control parameters, start-up current limit, sleep mode, direction, and diagnostic modes.The A8904 is fabricated in the Allegro® BCD (Bipolar CMOS DMOS) process, an advanced mixed-signal technology that combines bipolar, analog, and digital CMOS, with DMOS power devices. The device is provided in a 24-pin wide-body SOIC package, with 4 internally-fused leads for enhanced thermal dissipation (package LB), and a thin ( 100 mA. If the solution experiences ambient temperatures of greaterthan 70°C then Cfilter should be rated for 105°C. All resistors are at least 1/8 W and have a tolerance of ±5%. In noise-sensitive systems where electromagnetic interference is an issue, or to stabilize the current waveforms with certain motors, it may be necessary to add RC snubbers across the motor windings as shown in the application circuit on the next page. The A8904 solution should berelatively noise immune from the effects of switching voltage spikes etc. if the correct watchdog capacitor has been selected for optimum blanking and good layout practices are implemented. At the range of operating frequencies that the current pulses are drawn out of the load supply, it is the capacitance reactance as opposed to the ESR that dominates the overall impedance of the input filter, Cfilter.Therefore, it is possible to reduce conducted electromagnetic emissions further, by simply increasing the value of Cfilter. In extremely sensitive systems, it may be necessary to introduce a differential mode inductor in series with the load supply line. Layout considerations. The TSSOP part (A8904SLP) has three separate ground connections, analog, digital, and power that must be connected...
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