Stm32f411ceu6 reset after quectel EC200U-CNAA sends Message or data

[Kai_Satone]

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.

[Kai_Satone]

Ok, we have send them details. But earlier we have used ETA1090 and it worked properly on our custom PCB.

[mƎALLEm]

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@Kai_Satone wrote:

we got Brown-Out Reset (voltage dropped below threshold 1.7 V).

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Voltage drop means power supply is not able to deliver sufficient current / power.

Try to separate LTE and STM32 power supplies and supply LTE module with a lab power supply and monitor the current peaks. You need to check your power supply design to ensure whether it's able to deliver sufficient current during the current peaks (to my knowledge LTE is pulling a high level current when trying to connect to the network).

[Andrew Neil]

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@Kai_Satone wrote:

 earlier we have used ETA1090 and it worked properly on our custom PCB.

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Ok, but that's an issue with your design - nothing to do with ST or the STM32.

As far as the STM32 is concerned, I think the question has been answered: the STM32 is resetting because your power supply is browning-out - so you can mark this thread as solved.

As @mƎALLEm said, you could confirm this by supplying the LTE module from a known-good supply, separately from the STM32.

As to investigating why your design isn't working, compare & contrast this design with your previous (working) one(s)...