How to Design Printed Circuit Board for RAK3172 LoRaWAN Module

RAK3172 is a LoRaWAN module based on the STM32L4 microcontroller, optimized for low-power IoT applications.

 It is widely used in custom LoRaWAN boards due to its compact footprint,

 low current consumption, and support for both AT command and RUI3 development modes.

This guide highlights the key design considerations for creating a custom LoRaWAN end-device circuit board for low-power IoT applications, 

beginning with a basic schematic diagram of the RAK3172 LoRaWAN module and followed by an explanation of each section.

The following steps focus on specific parts of the design that require special attention.

1. Ensure that the RESET pin includes an external pull-up resistor and a bypass capacitor. The capacitor helps stabilize the signal on the reset line. Without it, the module may become susceptible to external interference, potentially causing unexpected resets. 

If the RAK3172 LoRaWAN module is deployed in a noisy environment, consider adding a second capacitor on this pin with a different value to complement the resonant frequency of the commonly used 100 nF capacitor.

2. UART2 is the most critical interface of the RAK3172 LoRaWAN module. It serves two key functions: accepting AT commands and enabling firmware updates.

Without a UART2 header or connector in the schematic, the module cannot be configured or updated, making the design unusable.

3. In relation to UART2, the header or connector must include the BOOT pin and be placed beside the VDD level. For RUI3 firmware updates, the BOOT pin is not required. 

However, in cases where a full chip erase is necessary or when uploading a complete .hex file to the RAK3172 LoRaWAN module, the BOOT pin must be pulled, and then STM32CubeProgrammer must be used.