Hi everyone,
I'm working on a project using an STM32F411CEU6 that communicates with a Quectel EC200U‑CNAA module via UART1. The system works fine for initializing the EC200U, sending AT commands, and even establishing a network connection. However, as soon as the EC200U starts transmitting data (e.g., sending an SMS or making an HTTP POST request), the STM32F411CEU6 resets.
the EC200U module is consumption during sending data and message is almost 3.6V 500mA.
what we have done:
-Added a large capacitor bank (1000 µF + 100 µF low‑ESR + 100 nF) directly across the EC200U’s VBAT pins, as recommended in the EC200U series hardware design manual with tandalam.
-Tested with a known‑good EC200U module and STM controller on bread board, the code works perfectly.
-Reduced the system clock from 100 MHz to a lower frequency – the resets still occurred.
Has anyone encountered similar resets when a cellular module starts transmitting? Could this be related to ground bounce, EMI coupling into the STM32’s NRST pin, or some unexpected interaction with the EC200U’s UART voltage levels?
Any insights or suggestions would be greatly appreciated.
Thanks in advance.
