MCU built for BLDC: With a new auxiliary timer

Renesas Electronics has announced the RL78/G1F series of multifunction microcontrollers, adding 20 new members to the RL78 family of low-power microcontrollers. With enhanced peripherals and compatibility with all RL78/G1x series microcontrollers, the new product further simplifies senorless brushless direct current motor (BLDC motor) control, providing high speed and high precision precision motor control for energy efficient household appliances and power tool applications.

As motor driven devices and power tools such as vacuum cleaners, dishwashers and refrigerators increasingly demand energy savings and system costs, traditional built-in position sensor motors are gradually being replaced by position sensorless brushless DC motors. The newly released RL78/G1F microcontroller integrates a high-speed three-phase PWM timer, a dedicated comparator, and an operational amplifier for high-speed sensorless control. Peripheral functions required for sensorless control, such as high-speed timers and comparators, reduce development costs while streamlining up to 20 external components. In addition, Renesas has added a dedicated motor control auxiliary timer to the motor control system to ensure better control over a wide speed range.

Key features of RL78/G1F Microcontroller:

(1) Special motor control subsystem, equipped with a new auxiliary timer, the maximum frequency up to 64 MHZ

The RL78/G1F series adds a motor control auxiliary timer with the same clock frequency to the existing Renesas microcontrollers' built-in pulse width modulated output (PWM) timer, which supports a maximum operating frequency of 64MHz. With the help of the timer and the high-speed comparator, the new microcontroller enables sensorless position sensing whether the rotor is at rest or at more than 30,000 revolutions per minute under 120-degree conduction control. As a result, complex motor control can be achieved at low cost, from initial start-up to acceleration to high-speed rotation.

(2) Programmable high conversion rate PGA reduces costs and simplifies the development process

The on-chip programmable gain amplifier (PGA) has a voltage conversion rate of up to 3.0V/μs(minimum), and the software can set the magnification between 4x and 32x. This enables voltage detection or overcurrent detection in brushless DC motor control without the need for an external amplifier. The PGA is equipped with input and feedback resistance ground pins to reduce the high current noise leading to the microcontroller during amplifier operation.

(3) The dual-channel high-speed comparator achieves reliable overcurrent detection and rotor position detection

The RL78/G1F series features a dual-channel high-speed comparator with a response time of only 70ns(typical), eliminating the need for an external comparator. One of the channels can use the output of PGA as an input signal to detect whether the frequency conversion circuit is overcurrent during the control of the brushless motor. The built-in function (PWMOPA) can use the comparator output to directly cut off the output signal of the inverter circuit for reliable overcurrent detection. The comparator in the other channel allows the user to select any combination of positive and negative stages in the four input pins to perform rotor position detection for sensorless brushless DC motor control to manage the motor's back electromotive force signal. Both channels support an external input reference voltage, an internal reference voltage, and the output of A dedicated D/A converter as a negative input.

(4)D/A converter and infrared (IrDA) communication function

The RL78/G1F series is equipped with single - or dual-channel D/A converters, a feature not previously available in equivalent flash memory sizes of 64KB and below. Renesas Electronics has also added IrDA support for serial communication functions, expanding the range of applications such as simple diagnostics, monitoring, electronic locks, handheld terminals, and more.

(5) The 4 mm × 4 mm package reduces component packaging and is suitable for more compact applications

The product range includes 24-pin HWQFN and 36-pin WFLGA 4mm×4mm square packaging. 36-pin WFLGA products are especially suitable for space-constrained equipment. Although the microcontroller has few pins, it supports dual power supplies, allowing the microcontroller to operate at 3V or 5V while communicating with external devices at 1.8V without the need for an external level converter. Internal sub-clock pulses or external input clocks enable low-power operation and intermittent operation at longer intervals to reduce power consumption and extend battery life.