Application of MSP430x09x series MCU in electric shavers

led2015

Application of MSP430x09x series MCU in electric shavers [Copy link]

Abstract MSP430x09x is the industry's first true 0.9V microcontroller (MCU) launched by TI. Its appearance makes it possible to use a single battery in portable devices, and will promote the development of single-cell powered, smaller and lower-cost portable products. Unlike existing MCUs that claim to use 0.9V technology, MSP430x09x can run all analog and digital logic at a low voltage of 0.9V, so this series of MCUs does not require an onboard boost converter, which can reduce power consumption for the overall system and reduce the need for external circuits. At the same time, while reducing the operating voltage, it still inherits the original excellent characteristics and rich peripherals of the MSP430 series microcontrollers, and pioneered the design of a feature-rich analog function module - the analog function pool (A-Pool). This article will introduce the application of the MSP430x09x series MCU in the electric shaver system, and focus on the software and hardware design of the system. 1 Introduction to MSP430x09x MSP430x09x is the first MCU in the MSP430 series of microcontrollers with a 0.9V operating voltage. This series is powerful and can be easily applied to micro motor control, infrared transmission, power detection and other occasions. In addition, its 0.9V operating characteristics can be widely used in single-battery powered consumer electronics. MSP430x09x contains a wealth of functional modules (see Figure 1). This series of solutions not only highly integrates 16-bit timers, watchdog timers, 11 I/Os with interrupt functions and zero-power low-voltage reset functions (BOR), but also integrates new analog function pool peripherals that can be configured as ADC, DAC, comparator, system voltage monitor (SVS) and temperature sensor, all with an operating voltage of only 0.9V. The 16-bit RISC architecture CPU and its instruction set are compatible with existing MSP430 MCU devices, with an operating frequency of up to 4MHz, and a power consumption of only 45μA/MHz in working mode. The MSP430x09x series supports three 0.9V MCU versions with up to 2kB RAM and 2kB ROM - MSP430L092 (RAM), MSP430C091 (ROM) and MSP430C092 (ROM), providing multiple options according to needs. This is because the 0.9V working characteristics cannot erase FLASH, so its application mode is to use EEPROM with L092 to complete the system design in the research and development stage, and use C09x with ROM after productization, which can run normally without EEPROM. 2 Analog Function Pool (A-Pool) The analog function pool developed by MSP430x09x is to realize various analog function modules under 0.9V. The specific implementation of a certain function is based on the user's software design. The reference voltage of the entire analog function pool module can be provided by an internal 256mV reference voltage or an external reference voltage. Multiple clock sources are available for it to choose as its clock source. In general, the analog function pool can realize the following functions: Comparator 8-bit digital-to-analog converter (DAC) System voltage monitor Internal temperature sensor Ultra-low reference voltage source The analog function pool looks complicated, but its core is actually a comparator and two multiplexers. The multiplexer is used to select the input signal of the positive and negative input terminals of the comparator to realize different functions. In addition, the operation of the ADC and DAC modules can realize more flexible and intelligent analog acquisition conversion functions through a variety of triggering methods. The programmable A-Pool can make various analog peripheral configurations run in an orderly manner without user intervention, thereby improving system flexibility. A-Pool also provides two AD sampling modes—RAMP and SAR mode. When using RAMP mode, it can work in no compensation mode, overload compensation mode, offset compensation mode, full compensation mode and window mode, etc. Of course, the higher the accuracy, the longer the required sampling period, so it is necessary to arrange the working mode reasonably according to the emphasis on sampling accuracy and sampling time. In addition, when the analog sampling voltage is greater than the reference voltage, the appropriate voltage sampling range can be set by software to complete the AD sampling of higher voltage, thereby eliminating the external voltage divider resistor, which greatly facilitates the user. As a powerful analog function module, the analog function pool can realize rich analog functions. In order to make it work better and avoid misoperation, please refer to the instructions in its user manual. 3 System structure block diagram and overall design plan (I didn’t fully understand the following after reading it for a long time, please explain it if you understand) Figure 2 Electric shaver system block diagram The electric shaver system block diagram in this article is shown in the figure above. In this solution, the electric shaver uses MSP430L092 as the MCU, and its ultra-low power consumption characteristics can make the shaver last longer. The operating voltage of all functions on the MSP430x09x chip is 0.9V, so when the system is powered by a single battery, no boost chip is required to make the system work normally. In this way, the same function is achieved, not only a battery is saved, but also the cost of the boost circuit is saved, and the entire system structure is very simple. The whole system is powered by a single battery for the MCU and 0.9V DC motor. The self-locking circuit is used to realize the functions of power on, speed selection and shutdown with a single button. The DC motor drive is realized by using a 0.9V MOSFET (due to the small rated current of a single 0.9V MOSFET, two MOSFETs are connected in parallel, which reduces the voltage drop on the MOSFET at the same time), and the PWM wave is used to control the on and off of the MOSFET to achieve motor speed regulation. Since the MSP430x09x series MCU has a powerful analog function pool, it can easily monitor the system power supply voltage. When it is lower than a certain voltage, the system is prevented from continuing to work to prevent permanent damage to the rechargeable battery due to excessive use. In addition, when charging, the battery voltage can be sampled through AD. When fully charged, the charging circuit is controlled by PWM to enter the trickle charging mode to achieve charging management. Users can use the comparator, AD, DA, internal temperature sensor and other functions of the analog function pool in the MSP430x09x to develop more advanced and more functional products. Since MSP430L092 is used in the product development stage, it only has RAM, so an external EEPROM is required for user programs. Since the operating voltage of EEPROM is 2.5~5.5V, a simple boost circuit is needed with independent components to load the running program from EEPROM during the L092 initialization phase. In the final product, C092 or C091 is used, and the external EEPROM part can be omitted.