MFRC522 May RX be connected to the other side of the antenna?

[Jeroen88]

Dear readers, in the MFRC522 reference design in the datasheet RX is connected to "TX1 side" of the antenna. May it also be connected to the other side, the "TX2 side"? This makes routing easier! Best regards, Jeroen

[EduardoZamora]

Hello @Jeroen88

Hope you are doing well.

Please, consider that MFRC522 is Not Recommended for New Designs. For new designs, consider using recommended product CLRC663 plus. If your development is on an early stage, I would strongly recommend moving to CLRC663 Plus, as it may help you to speed up your project. If you are still planning using the device that is Not Recommended for New Designs, please keep in mind that you may face some supply issues in a future. I truly apologize for any inconvenience this might cause you.

Could you please confirm if you are referring to R2 from MFRC522 Data Sheet, Fig 27. Typical application diagram? If so, R1 and R2 form a voltage divider which has to be adjusted according to the incoming voltage levels at UC0 (see Antenna design for MFRC52x, Fig 12. Receiver Circuit). Please, consider following the typical/recommended applications. For more information on this, please take a look at the Antenna design for MFRC52x, Chapter 4.6 Receiver circuit design.

Regards,
Eduardo.

[Jeroen88]

Hi Eduardo, another question, I found the online tool for antenna simulation and computation of the impedance matching components. Could you give a formula with given values from that simulation and computation to compute R1, R2 and Crxn (assuming that the RXp side is the same). What is a suggested value for Cvmid? I am referring to CLRC663 datasheet figure 36. Thank you for your kind answers! Jeroen

[EduardoZamora]

Hi,

Connecting R2 to TX2 may be possible; however, please consider that we cannot guarantee the proper functioning of your device as it is not the recommended design.

Perhaps you can refer to the NFC Antenna Design Online Training series, Part 4 Optimization & Debugging, ~min 14:40. There you can find information about the Receiver circuit and some components considerations.

Regards,
Eduardo.

[Jeroen88]

Hi Eduardo,

I switched to the CLRC663, thanks for the advice!

I have watched the videos and it is suggested to measure the voltage at the RX pin and adjust the resistors accordingly. Would it be possible to get a reasonable value of the resistors from the simulation on the website without measuring the load under different circumstances?

Best, Jeroen

[EduardoZamora]

Hi,

As mentioned in the NFC Antenna Design Online Training, it is highly recommended to perform the measure under different real loading conditions to ensure that your device will work properly under these conditions and that the communication will not be affected. Otherwise, we cannot guarantee the proper functionality of your device.

I apologize for the inconvenience.

Regards,
Eduardo.

[Jeroen88]

Hi Eduardo,

Thank you for your reply,

I will check the datasheet of the CLRC663 plus.

Yes I am referring to that figure. The schematic is clear. I am not very experienced in RF technology, but I would consider it possible that the matching circuit together with the antenna is symmetrical. Would it work to connect R2 to the conductor at TX2? That would, taking the pin layout of the chip, make routing way more easy. If not, would it be better to route the part of the circuit at RX at the backside of the PCB using vias, or rather the part at TX2?

Best regards, Jeroen