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.

[MHoll.2]

Hard to say with so little info.

- The LTE1+ Module can draw up to 3A peek current, is You power supply able to supply this?

- Did You check the 3V3 supply with an oscilloscope when the reset happens?

- Is there someting connected to the NRST Pin of the STM32, if yes, then You should have a Capacitor on this line (100nF is a tipical value)

Can You show a part of You schematics, and possible layout?

[Kai_Satone]

1} yes ,we are providing 3.5 V 4 A via power supply.

2}Yes , we have check using oscilloscope, after sending message or data on server , it gives spikes.

3} i have shared images of schematics . we have connected 2.2uF capacitor to NRST pin.

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Edited to re-size images to a legible size

[MHoll.2]

OK, this looks good to me, my only remarks are:

- The current limit of the Boost converter is set to 3.6A,  but according to the datsheet the effective current limit can be between 2.6 and 4.6A. Assuming that VCC is 3.3V this means the max. output current can be somewere between 2.2A and 4A

- The DTC043ZEBTL is an NPN Transister, but the schematic calls for an PNP (probably working because you are using the B-C Junction as diode).

To investigate the problem You can try to read the RCC_CSR register after the reset.

[Andrew Neil]

Is this on a custom PCB?

If so:

• you'll also need to show your layout.
• Some good, clear photos would also help.
• Did you prototype it on known-good development boards first?

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@Kai_Satone wrote:

2} we have check using oscilloscope, after sending message or data on server , it gives spikes.

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Please show a scope trace(s).

Please use your scope's trace capture facility rather than trying to photograph the screen.

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@Kai_Satone wrote:

Has anyone encountered similar resets when a cellular module starts transmitting?

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Yes - it's a common issue!

Spikes, droops, and/or noise could certainly cause the MCU to reboot.

As @MHoll.2 said, check RCC_CSR  for the reset cause.

[Kai_Satone]

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

[Andrew Neil]

So it is a power supply issue - your supply is dropping under the load of the TX.