As motor control applications in China mature, there is a growing need for MCU products specifically designed for the Chinese market, capable of achieving high processing performance with minimal power consumption, enhanced computing power, and peripheral device functionality.
Under the dual pressures of energy shortages and stringent environmental requirements, higher energy efficiency, superior dynamic performance, and lower operating noise have become inevitable trends in motor drive design. Therefore, the shift from traditional AC motor design to brushless DC motors (BLDC)/stepper motors (SM), which offer advantages in efficiency, noise, weight, and lifespan, is becoming a hot topic for motor control application designers.
120° DC brushless motor and stepper motor control methods
As is well known, the three Hall sensors are spaced 120° apart, and each Hall signal switches according to the direction of the rotating magnetic pole. Based on the state of the three Hall signals, position information can be obtained every 60° (there are 6 modes per cycle). If the conduction mode of each phase changes according to this timing, then the rotating magnetic flux will be generated as shown in the figure below, thereby giving the rotor torque and causing it to rotate.
Figure 1. Range of six conduction modes and rotor positions.
The motor's rotational speed is calculated by the difference between the current timer count and the timer count 2π [rad] prior. The timer count is obtained via an external interrupt triggered by a Hall effect signal, during which the timer TAU continuously counts freely. This speed measurement method is applicable even if there are positional deviations among the three Hall effect sensors.
To start the motor and obtain rotor position information, a 60° starting sequence is required. This triggers the external interrupt corresponding to the Hall signal and continuously performs commutation control, thus starting the motor to rotate. The duty cycle adjustment value at any given time (n) is calculated using the following formula, thereby regulating the motor's rotational speed.
A stepper motor is an open-loop controlled motor that converts electrical pulse signals into angular or linear displacement. Under non-overload conditions, the motor's speed and stopping position depend only on the frequency and number of pulse signals, and are unaffected by load changes. When a stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in a set direction, called the "step angle." Its rotation occurs step by step at fixed angles. The angular displacement can be controlled by controlling the number of pulses, thus achieving accurate positioning. The speed and acceleration of the motor can also be controlled by controlling the pulse frequency, thus achieving speed regulation.
Figure 2 Stepper motor principle
Designed specifically for the Chinese market
In response to the increasingly mature motor control applications in China, Renesas Electronics has launched a number of MCU products specifically for the Chinese market, aiming to achieve high processing performance through the lowest power consumption, enhanced computing power and peripheral device functions.
R7F0C009 series
The R7F0C009 is a pin-less microcontroller developed by Renesas Electronics specifically for applications requiring control of brushless DC motors, such as electric bicycles, power tools, and home appliances. Utilizing the RL78 core, it not only features a high-precision (±2%) on-chip oscillator, a 24MHz CPU, and other standard built-in functions, but also incorporates multipliers, dividers, and multiply-accumulator instructions from the R8C family. It includes verifiable trace logging features such as timers RD/RJ, an event linker , one operational amplifier, and two analog comparators, enabling system architecture at a lower overall cost, achieving a more compact size and lower power consumption.
Figure 3 R7F0C009 Module Block Diagram
This series of MCUs features 30-44 pins, a maximum of 16K Flash memory, and integrates up to 12 channels of ADC and a dedicated timer RD for motor control in three-phase PWM drive. Because it can output three pairs of non-overlapping positive and negative PWM waveforms, it is particularly suitable for brushless DC motors.
Figure 4 shows the dedicated timer RD for motor control used in three-phase PWM drive.
Event Link Controller (ELC) can improve motor control performance by using timers to trigger (automatic/delayed) A/D sampling without CPU intervention.
Figure 5 Event Link Controller (ELC) Function
The R7F0C009 MCU also integrates a programmable gain amplifier and a comparator, supporting 2-channel comparison (high/low speed selectable), high-speed remote travel mode (motor current feedback to prevent overcurrent protection) and low-power low-speed remote travel mode (battery detection), which can be used for current monitoring and protection.
Figure 6 shows the unique programmable gain amplifier/comparator of the R7F0C009.
In addition, most pins of the MCU can support high current output of 40mA, which can reduce the number of external drive components and further reduce costs. Renesas Electronics also provides reference designs for electric bicycle controllers and brushless DC power tools for motor control microcontrollers, shortening customers' start-up time and product development cycle.
R7F0C014 series
The R7F0C014 series of microcontrollers targets markets such as inverter motor control, software modems, home appliances, mobile devices, medical and healthcare devices and other consumer electronics, office equipment, and industrial equipment. This series also uses the RL78 core and is available in 32-pin LQFP (0.8mm pin pitch) and 64-pin (0.5mm and 0.65mm pin pitch) packages.
The R7F0C014 not only features a high-precision (±1%) on-chip oscillator, a 32MHz CPU, and other standard built-in functions, but also incorporates multipliers, dividers, and multiply-accumulators from the R8C family, which offer faster processing speeds than the RL78/G13 series. It also includes verifiable traceability features such as timers RD/RG for three-phase PWM drives, data transfer controllers, and event link controllers, enabling system architecture at a lower overall cost, resulting in a more compact size and lower power consumption.
In addition, it supports wide voltage operation (1.6V-5.5V operating voltage) and has a large number of built-in functions to support functional safety (such as A/D converter testing function), as well as large-capacity Flash (128KB Flash, 8KB RAM, 8KB data Flash). Users can add a large amount of safety-related code to comply with IEC and safety regulations.
Figure 7 R7F0C014 Module Block Diagram
R7F0C806/807 series
The R7F0C806/807 series microcontrollers feature a high-precision ±2% on-chip oscillator (TA=0+40℃), enabling CPU operation up to 20MHz. They also incorporate optional power-on reset and a watchdog timer, facilitating a more compact size and lower power consumption, thus reducing overall system setup costs. Furthermore, the R7F0C806/807 integrates real-time output control circuitry, enabling simultaneous 8-channel output via timer PWM, which is beneficial for customers developing brushless DC motor control and stepper motor control (controlling two simultaneously).
This product series features 20-pin SSOP and SOP packages, as well as a 4KB-8KB flash memory lineup, making it more suitable for small home appliances and general consumer product applications.
Figure 8. Block diagram of R7F0C806/807 module
In practical applications, the PWM output function of TAU can be used to control one DC motor or two stepper motors; the output can be cut off by generating an interrupt caused by INTP0; through software settings, four outputs can be selected: Hi-Z output, low-level output, high-level output, and output cut-off when forced to cut off.
Figure 9 R7F0C806/807 Real-time Output Control Circuit
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