Developers have been facing constructing small, reliable, low-power, and low-cost battery-powered Bluetooth devices, while meeting shorter listing time windows. This is a workaround matrix becoming more difficult, but because the semiconductor vendor's innovative solution helps solve these specific problems, it is not impossible.
One of the solutions is to integrate STM32WB55RGV6 microcontrollers of semiconductors that integrate control processors and Bluetooth radios.
Before introducing STM32WB55RGV6, this article will elaborate the design requirements of the growing Bluetooth accessories market and how to apply it.
Bluetooth accessories
Bluetooth accessories typically have the same requirements as the battery life and size. For consumer Bluetooth products, longer battery life is directly related to customer satisfaction, so small size and low power components should be selected. The initial design should have sufficient alternative flexibility, because with the development process, it is not uncommon to find better products than the selected product.
Bluetooth design is usually divided into three parts: Bluetooth radio, application processor and support components, and user interfaces (buttons, LEDs, speakers). STMicroelectronics simplifies design by integrating control processors and Bluetooth radios on the same microcontroller. The microcontroller STM32WB55RGV6 is a part of the STM32WB microcontroller family that has a 64 MHz (MHz) integrated arm® Cortex®-M4 floating-point unit (FPU) processor and a single chip full Bluetooth radio on a single chip. Device. Onboard memory includes a 1 megabyte (mbyte) flash memory and a SRAM of 256 kilobytes (kbytes).
The STM32WB55RGV6 has three in-slide regulators. The main processor runs when the processor is running and sleep mode. Low-power regulators are used for low power operation and low power dormancy mode. The RF (RF) regulator is only used to power the Bluetooth radio and the RF subsystem.
There are other parameters clearly indicate that STM32WB55RGV6 is built for low power applications. It has 13 Na'an (NA) shutdown mode, which can turn off all the contents on the chip, except for some RAM. If the real-time clock (RTC) remains in shutdown, the device consumes only 315 NA. In the case of RTC operation, the microcontroller can also retain 32 kB of RAM while consumes only 600 NA.
In order to improve flexibility, STM32WB55RGV6 has full range of peripherals, including two serial peripheral interfaces (SPIs), and two I 2 C interfaces (Figure 1). USB 2.0 Full Speed (FS) port can be used to transfer files between applications and PCs. It can also be used to charge the battery on the Bluetooth application, whether or not data transmission is supported. The STM32WB55 also has a controller for external 8 x 40 LCD. Touch sensor controller can be used to enable touch screen interface.
Bluetooth radio on STM32WB55RGV6 complies with the latest Bluetooth specification V5.0. The radio is also compliant with the IEEE 802.15.4-2011 specification for Bluetooth radio physical layer (PHY) and media access controller (MAC). For battery-powered applications, radio is compliant with Bluetooth low power consumption (BLE) standard, and supports 1 megabyte / sec (Mbit / s) and 2 MbitS / s data rates via secure connection.
BLE stack and IEEE 802.15.4 PHY and MAC layers run on a dedicated ARM Cortex-M0 + CPU on STM32WB. This Cortex-M0 + is dedicated to running only the BLE stack and cannot be used to run the user application code.
The RF front end of the STM32WB55RGV6 microcontroller series is designed for the minimum external component, as shown in Figure 2. It has a dedicated switch mode power supply (SMPS) for powering the RF circuit.
SMPS is a good example of how integrated solutions to solve the problem. In order to minimize interference to the RF circuit, SMPS uses the same clock frequency as the RF portion as a Cortex-M0 + microcontroller (4 or 8 MHz). In order to further reduce interference, automatic gain control (AGC) can automatically reduce the RF and IF gain. The firmware can also manually trim the AGC.
The RF part requires little external components. To achieve this, the front end of the RF has a user-programable chip capacitor, so the outer 32 MHz crystal does not require an external fine-tuning capacitor. The RF front end also reduces the number of components by seeing a complete band-pass Barron near the antenna pin (RF1) (Figure 2, again).
The RF1 pin must be connected to a compatible Bluetooth 2.4 gigan (GHz) antenna by a filter with a low-pass matching network. Finally, it is necessary to decouple the capacitor between the power supply and the ground in the RF part. The recommended value is 100 ps. (NF) and a 100-skinned (PF) connected in parallel.
Like any radio application, RF design and component selection directly affect Bluetooth radio performance. Use high-precision components will increase the reliability of Bluetooth radios. For designers, most of the work in the RF part has been completed. The system is designed by the developer to make it not hindering the path between the external Bluetooth antenna and the pairing device.
In order to help speed up the development of STM32WB55RGV6, the semiconductor provides a P-Nucleo-WB55 Nucleo development board (Figure 3). The motherboard is also equipped with a USB encrypted dog, which also has a STM32WB microcontroller.
The Nucleo board has an ArduinoTM extension connector that allows developers to use Arduino UNO compatible mask to enhance their projects. Developers can quickly assemble hardware prototypes around Nucleo boards. The Nucleo application is programmed and debugged by connecting the PC to the USB connector on the board. The programmed Nucleo board can then communicate with the Bluetooth adapter supplied or Bluetooth.
Application security
The security of wireless applications has become the main concerns of developers. The company needs to protect their data and firmware from attacks and unauthorized forgery. The AES-256 hardware encryption module on STN32WB55RGV6 can be used to encrypt and decrypt Bluetooth transmission. This prevents malicious behavior from spriring Bluetooth transmission and capturing data.
Applications are common to update through Bluetooth. However, this can also provide hackers with an attack point for installing false firmware updates. STM32WB55RGV6 prevents errors from installing by a secure firmware installation (SFI) process. This is a public key / private key system that transmits the encrypted firmware file to STM32WB55RGV6. STM32WB55RGV6 decrypts firmware files using the readable public key signed by private key and intention-semiconductor stored in its secure memory block. This ensures that only the firmware with authorized credentials can update the firmware.
Each STM32WB55RGV6 also has a unique 96-bit identifier (ID) and a unique 64-bit ID. These can be used to identify different STM32WB55RGV6 microcontrollers to improve security, and even enable different functions for firmware of different systems.
Conclusion
The development of Bluetooth devices requires strict control of power, size, cost, and reliability. Select highly integrated components (such as STM32WB55RGV6) can greatly simplify design staff's trade-off matrices and minimize development time.
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