NFC design using ST25R3916B and ST25DV04KC

[kiranym]

Hi,

We are planning to use ST part# ST25R3916B in one of our projects. The product is targeted for European market, and it might also be targeted to US and other global markets as well. Could you help us to know the various design aspects (Electrical and software) we need to take care from NFC certification point of view (considering the target counties) for the NFC design using ST25R3916B (NFC reader) and ST25DV04KC (Tag IC), if any please?

In our application, the tag antenna will be placed on a metal surface along with the ferrite sheet. We would like to set antenna impedance to a value of around 15 ohms. Could you help us to know the preferred position of the smith chart’s inner loop and the 13.56MHz point for this application considering a reading distance of about 7 to 8cm please? Please let us know the optimum antenna impedance value, if 15 ohms is not OK.

Thank you,

Kiran

[Travis Palmer · Accepted solution]

Hello Kiranym,

The ST25R3916B is a perfect choice. As far as I know, for US and Canadian Market you have to fulfill FCC standards.

For EU you need to comply with CE / RED. This can depend on your type of application. The best approach is, if you consult an accredited lab. 

The ST25R3916B test reports can be found here: https://fccid.io/YCPR3916BD1/

You mentioned:

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In our application, the tag antenna will be placed on a metal surface along with the ferrite sheet. We would like to set antenna impedance to a value of around 15 ohms.

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Will the tag antenna or reader antenna be placed on the metal sheet? To achieve 7cm of read range should be feasible with a proper antenna (e.g. 7x7cm). You can start using our EVAL board for prototyping, which has a 66x66mm antenna.

Also 15Ohm should be a good start. You will see if you can higher or need to lower the target matching impedance.

AN5276 should give a good example of how to place them matching impedance inside the smith chart. Please be aware we also have the antenna matching tool (STSW-ST25R004) as well as the eDesignsuite.

https://eds.st.com/nfc-tuningcircuit/

please let us know, if you have further questions.

br Travis

[kiranym]

Thank you, for the information and kind help.

The tag antenna will be mounted on a curved metal sheet. But, the reader antenna will not be mounted on a metal surface.