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Nikunj_17
Graduate
October 25, 2024
Solved

Issues with ST25DV04KC-IE8C3 NFC Chip Interference from Magnetic Switch

  • October 25, 2024
  • 1 reply
  • 1267 views

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!

    This topic has been closed for replies.
    Best answer by JL. Lebon

    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.

    1 reply

    J
    JL. LebonAnswer
    ST Employee
    October 25, 2024

    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.

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