MICROCONTROLLER SOLUTIONS

Motor Controller Offers DSP Performance at the Price of an 8-Bit Micro

STMicroelectronics’ ST7FMC series of 8-bit microcontrollers provides high performance and low system cost in motor control applications. Intended for use in products from refrigerators to automobiles, they can dramatically improve the energy efficiency of all kinds of fans, pumps and compressor assemblies.



The family offers substantial advantages over competing DSP-based control solutions, which are both more costly and more difficult to implement. This is largely due to the provision of an on-chip motor control peripheral, the MTC, which incorporates a three-phase Pulse Width Modulator (PWM) multiplexed on six high-sink outputs, with a highly flexible Back EMF (BEMF) zero-crossing detector and co-processor unit.

The MTC makes the devices particularly suitable for the sensorless control of permanent magnet BrushLess Direct Current (BLDC) motors. A patented 'three-resistor' sensorless control method, in conjunction with on-chip comparators and an op-amp, provide the lowest possible system cost and the highest system integration for such applications.

By offloading motor control tasks on to the MTC, STMicroelectronics has freed up some 70% of the CPU’s processing power for the rest of the application. As a result, the device can handle both motion and higher level functions, opening up new capabilities compared to traditional three-phase brushless solutions.

The devices’ input pins can also be configured for Hall, tachometer or encoder sensing. In addition, comprehensive filters and configuration options allow the control of any star or delta wound motor, from 12V to 240V, in various control topologies (six-step/sine wave, current/voltage, PAM/PWM). This versatility makes it the ideal platform for designers working with multiple motor control topologies.

Based on an industry standard 8-bit core, the devices are available in pin-compatible dual-voltage Flash memory and ROM versions, from 8Kbyte to 60Kbyte, and in various packages ranging from the 32-pin TQFP32 (7mm x 7mm) to the 80-pin TQFP80 (14mm x 14mm). Software control over four power-saving modes allows power consumption to be minimised.

As well as the motor control peripheral, the devices feature a 10-bit ADC, Serial Peripheral Interface (SPI), Local Interconnect Network Serial Communications Interface (LINSCI) for automotive applications, five 8-bit and 16-bit timers, and up to 60 general-purpose I/Os.

In keeping with their intended use, the ST7FMC family also includes a wide range of safety and reliability features. These include an embedded secure reset circuit with low voltage detector, and multiple clock sources with Clock Security System (CSS), all under System Integrity management. The MTC’s programmable filters and windowing mechanisms also contribute to reliability by assisting operation under high ambient noise conditions, and in the event of sudden torque variations. A hardware asynchronous ‘emergency stop’ provides efficient protection for power stages.

Features

• 8-bit micro with integral motor controller
• Substantial processing power for higher level functions
• Integrated Pulse Width Modulator
• Integrated Back EMF sensor for sensorless operation
• Configurable for Hall, tachometer or encoder sensing
• Controls any star or delta-wound motor, from 12V to 240V
• Six-step/sine wave, current/voltage, PAM/PWM topologies
• Integrated safety and reliability features
• Pin-compatible Flash and ROM-based versions from 8Kbyte to 60Kbyte
• Full range of standard micro interfaces and peripherals
• Package options from 32-pin TQFP32 (7mm x 7mm) to 80-pin TQFP80 (14mm x 14mm)
• Temperature Range -40°C to +85°C

Applications

• Air conditioners
• Refrigerators
• Washing machines
• Automotive fans and pumps
• HVAC (Heating, Ventilation and Air Conditioning) fans and actuators
• Office automation
• Electric vehicles
• Low-end to medium industrial drives

To support developers with the implementation of ST7FMC designs, STMicroelectronics offers free libraries for BLDC and 3-phase induction motor applications. These libraries can be downloaded free of charge from the software page of the STMicroelectronics MCU website, which can be reached by clicking on the link on the right.

For further information, including the ST7MC Family Datasheet, please click here