NFC port spec. Coil inductance

[Andrew Lohmann]

I wish to design a Laird BL652 Bluetooth with an NFC port. Unfortunately I have not been able to discover the coil inductance. They use a Nordic nRF52832 chipset.

My hope is that you may have an application circuit that will indicate what is required. For example I am using a long range NFC using M24LRxx ST in another product with a 4u7H PA6512 CoilCraft NFC aerial.

The application is small and we plan to use a CR2477 lithium button primary cell. This to be connected to VCC in series with a protective resistor. The NFC circuit and the debugging interface must not charge the battery

[Jørn]

The closest thing we have would be our nRF52 Devkit (pca10040). All nRF52 devkits come with a NFC tag, the layout for the tag is included in the kits hardware files. It should have an inductance of around 720nH. The tuning capacitors of the Devkit are 300 pF, however that would change depending on your layout. There is not one specific inductance value to use, it depends on what you're interfacing with or design requirements. I'm not an NFC expert, but from what I've found the most important features of the NFC antennas are that transmitter and receiver geometries are similar, as this increases the coupling coefficient, so you should design the antenna to roughly match the antenna you're interfacing with, and then choose capacitors to ensure it resonates at 13.56MHz.