A8904SLB

A8904 3-Phase Brushless DC Motor Controller/Driver with Back EMF Sensing Features and Benefits Description ▪ Pin-for-pin replacement for A8902CLBA ▪ Start-up commutation 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-out ported in real time ▪ Dynamic braking through serial port or external terminal 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 back EMF 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. Packages: Not to scale 28-pin TSSOP with exposed thermal pad (Package LP) 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 greater than 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 be relatively 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 together externally. A ground plane should be used to provide heat sinking for the power switches and the reduction of potential noise pick-up through inductive loops and radiated emissions. The ground plane should cover the area beneath the A8904 and extend beyond the outline to form a plane around all the external components. The exposed thermal pad of the TSSOP part should be connected to the ground plane. Filter components, especially Cfilter, timing, and delay capacitors should be positioned as close as possible to the device terminals. It is also imperative that the traces to the serial port and oscillator are as short and as wide as possible to reduce stray inductance and prevent potential data corruption. In addition, these traces should be positioned well away from any noisy signals. Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 15 A8904 3-Phase Brushless DC Motor Controller/Driver with Back EMF Sensing Typical application (LB package) Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 16 3-Phase Brushless DC Motor Controller/Driver with Back EMF Sensing A8904 LB package, 24-pin SOICW 15.40±0.20 4° ±4 24 24 +0.07 0.27 –0.06 10.30±0.33 7.50±0.10 A 1 2.20 9.60 +0.44 0.84 –0.43 2 1 2 0.65 1.27 0.25 24X SEATING PLANE 0.10 C 0.41 ±0.10 1.27 C B PCB Layout Reference View SEATING PLANE GAUGE PLANE 2.65 MAX 0.20 ±0.10 For reference only Pins 6 and 7, and 18 and 19 internally fused Dimensions in millimeters (Reference JEDEC MS-013 AD) Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area B Reference pad layout (reference IPC SOIC127P1030X265-24M) All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances LP package, 28-pin TSSOP with exposed thermal pad 0.45 9.70 ±0.10 28 +0.05 0.15 –0.06 0.65 28 4° ±4 1.65 B 3.00 4.40 ±0.10 6.40 ±0.20 3.00 6.10 0.60 ±0.15 A 1 (1.00) 2 5.00 0.25 28X SEATING PLANE 0.10 C +0.05 0.25 –0.06 0.65 C SEATING PLANE GAUGE PLANE 1 2 5.00 C PCB Layout Reference View 1.20 MAX 0.10 MAX For reference only (reference JEDEC MO-153 AET) Dimensions in millimeters Dimensions exclusive of mold flash, gate burrs, and dambar protrusions Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area B Exposed thermal pad (bottom surface) C Reference land pattern layout (reference IPC7351 SOP65P640X120-29CM); All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and PCB layout tolerances; when mounting on a multilayer PCB, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5) Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 17 A8904 3-Phase Brushless DC Motor Controller/Driver with Back EMF Sensing Copyright ©2003-2008, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the failure of that life support device or system, or to affect the safety or effectiveness of that device or system. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. For the latest version of this document, visit our website: www.allegromicro.com Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 18