Issues with ST25DV04KC-IE8C3 NFC Chip Interference from Magnetic Switch

[Nikunj_17]

Hello STM Community,

I'm currently working on a project involving the ST25DV04KC-IE8C3 NFC chip interfaced with the STM32L496ZG microcontroller. I've encountered an issue where the performance of the NFC chip deteriorates when a magnet is brought near the system, specifically related to the operation of a magnetic switch that generates interrupts.

Problem Description:

• Components: The NFC chip is located approximately 3.6 mm away from a magnetic switch (RR132-2E32-551).
• Issue: When the magnet is brought close to the magnetic switch, it appears to cause delays in counting and issues with I2C communication. Specifically, I suspect that the magnetic field is affecting the NFC chip's operation, leading to unexpected behaviour or interruptions that impact the STM32’s performance.
• Effects on System:
  • Interruption in the NFC communication.
  • Possible noise was introduced on the I2C bus.
  • Delays in processing and timing, particularly in counting routines.

Troubleshooting Steps:

• I’ve monitored the interrupt lines and found unexpected behaviour, suggesting that the magnet may be inducing noise or causing the NFC chip to misbehave.
• I am considering moving the NFC chip to the bottom layer of the PCB and implementing shielding to mitigate the interference.

PCB Design:

I have attached a photo of the PCB layout for your reference. I would greatly appreciate any feedback on the design or suggestions on mitigating this issue!

Thank you for your assistance!

[JL. Lebon · Accepted solution]

Hello, 

NFC is based on magnetic coupling between the reader and the tag. The reader is emitting a magnetic field at 13.56MHz that is captured by the tag's antenna, creating current into the antenna. Having a magnet nearby may disturb the magnetic field emitted by the reader.

Does the issue appear when there is a reader communicating with the tag and a magnet is put close to the switch? Or do you have issues when there is no RF reader in front of the tag?

Best regards.