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]

Hello Andrew

What do you mean you have not been able to discover the coil inductance?

You can find information on tuning the NFC antenna in this whitepaper. For the NFC to function properly its antenna must be tuned to resonate at 13.56MHz, which is done by combining the antenna coil inductance with tuning capacitors. As is stated in the white-paper, the total capacitance is a combination of Cp which is the PCB parasitics, and Cint which is the internal capacitance plus pad parasitics.

So typically you would choose/design the antenna with a given inductance, then find the PCB parasitics due to your board layout, and then calculate the tuning capacitors necessary to have the antenna resonate at 13.56MHz.

Best regards

Jørn Frøysa