FLEX-ST25DV64KC Tuning Capacitor value

[DavidG7]

Hi,

We have duplicated the design onto our own NFC tag, copying the same antenna design onto a flexi pcb

What should be the tuning capacitor for this coil be for NFC ?

If thats not available, what is the inductance value of the antenna so we can try and calculate it ourselves.

Ultimately we will tune it but we would like to start with at least an approximation

[Henry Crane · Accepted solution]

Hello DavidG7,

the FLEX-ST25DV64KC antenna coil has been designed for the internal tuning capictance of our ST25DV64KC type V tag IC which is 28.5pF.

As you can see on the schematic available at https://www.st.com/resource/en/schematic_pack/st25dv64kc-disco-flex-ant-schematics.pdf, there is a parallel optional tuning capacitance C4 which is not populated.

Since this coil design is a single layer coil, you can copy it on any PCB substrate and you'll get similar inductance, a,d final tag tuning frequency as our kit.

Feel free to contact us if we did not answer to your question.

regards,

Henry Crane NFC tag IC support team