C8051F850-BLDC-RD Silicon Labs

AN794 C8051F850 BLDC REFERENCE DESIGN KIT 1. Introduction This design kit provides a complete system-level solution for sensorless, brushless dc (BLDC) motors. This application note includes complete schematics, PCB layouts and firmware. This kit supports 3-phase BLDC motors that meet the following specifications: Trapezoidal back-EMF Max operating voltage of between 10 V to 24 V dc 24 kHz PWM frequency Maximum average current of 10 A Maximum speed not exceeding 200,000 rpm for a 2-pole BLDC motor Overcurrent detection capability stops the motor when average current exceeds 10 A. Motor Stall detect capability stops the motor when a motor stall is detected or extreme loads encountered. Tachometer Frequency Generator (FG) output signal The kit aims to demonstrate the capabilities of the C8051F850 for operating BLDC motors. The unique features offered by this MCU for BLDC motor operation are: PWM synchronized blanking of comparator for BEMF Zero-Crossing Detection Automatic PWM duty cycle reduction to limit motor current during startup Hyperdrive mode to increase the maximum speed of some motors 1.1. Kit Contents The kit consists of the following: One MCU Board: MCRD-MCU-C8051F850 with the motor control firmware preprogrammed into the MCU One Powertrain Board: MCRD-PWR-NLV-F85X One BLDC Motor: Turnigy 450 Series 3800 kV Brushless Outrunner Helicopter Motor One Motor Mount Board One 8-bit MCU Kit CD One 12 V, 5 Amp Universal Input Power Adapter Rev 0.1 10/13 Copyright 2013 by Silicon Laboratories AN794AN794 1.2. Operational Specifications The kit uses the Turnigy 450 Series 3800 kV Brushless Outrunner Helicopter Motor. The motor operating range and specifications are given in Table 1. Table 1. Motor Specifications Parameter Min Typ Max Unit Number of poles 6 Operating voltage 7.4 14.8 V Maximum current 35 A Maximum power 365 W No-load full-speed average current 12 V 3.66 A No-load peak startup current 12 V 11 A Motor constant 3800 RPM/V Maximum speed 12 V 45600 RPM Weight 80 g The operating ranges of the hardware and firmware in the kit are shown in Table 2. Table 2. Hardware and Firmware Operating Range Parameter Min Typ Max Unit Power supply 10 24 V Motor driver PWM frequency 24 kHz Continuous average output current 10 A Speed range (2-pole motor) 2250 200000 RPM Speed range (4-pole motor) 1125 100000 RPM Speed range (6-pole motor) 750 66667 RPM In the default operation mode using the ac/dc adapter, the operating parameters of the motor are shown in Table 3. Table 3. Reference Design Kit Operating Specifications Parameter Value Unit Power supply 12 V No-load full-speed average current 12 V 3.66 A No-load peak startup current 12 V 11 A Maximum speed 12 V 45600 RPM Motor driver PWM frequency 24 kHz Maximum Power 43.92 W 2 Rev 0.1