nRF52832 - Initial values for capacitors for NFC coil

RE: nRF52832 - Initial values for capacitors for NFC coil

Kaja — Mon, 19 Oct 2020 14:51:31 GMT

Hi,

Cp ~ represent the parasitic capacitances between the PCB pads of the crystal, the tracks in the crystal circuitry and, the pads of the nRF device to ground.

Best regards,
Kaja

RE: nRF52832 - Initial values for capacitors for NFC coil

HAP — Thu, 15 Oct 2020 14:04:07 GMT

Hi Kaja

Is Cp parasitic capacitance of PCB Wires antenna?

Best regards
HAP

RE: nRF52832 - Initial values for capacitors for NFC coil

Kaja — Mon, 10 Aug 2020 13:56:31 GMT

Hi Jeferson,

it looks correct! Just add Cp ~1 pF as well, but that gives same result.

FIY: you should still adjust values on the physical board, as it might deviate a bit from the theoretical value.

Best regards,
Kaja

RE: nRF52832 - Initial values for capacitors for NFC coil

Abomin3v3l — Wed, 05 Aug 2020 23:44:18 GMT

Hi Kaja.
Could you please check if my calculations are correct?
Regards.

RE: nRF52832 - Initial values for capacitors for NFC coil

Abomin3v3l — Tue, 04 Aug 2020 21:46:13 GMT

Hi Kaja.
I really apreciate your help.

There is no ground arm nor other signals on the antenna area.

I did added more two capacitors, one on each NFC pin, on each end of the antenna.

The estimated inductance is 1.08uH, so here goes my calculation.

This part of equation:

((2*pi*13.56*1000000)^2) * 1.08*10^-6
Result = 7.839*10^9

Now doing substituition on the complete equation:

Ctune = (2/(7.839*10^9)) - 0 - 4*10^-12
Ctune = 2.511*10^-10
Ctune = 251pF
Ctune = 220pF + 30pF (commercial values)

Does this seem correct for you?

Regards,
Jeferson.

RE: nRF52832 - Initial values for capacitors for NFC coil

Kaja — Fri, 31 Jul 2020 12:08:15 GMT

Hi Jeferson,

you can estimate the values or you can tune the antenna, see our white paper.

We can help you with antenna tuning, you should remove the ground arm under the antenna.

Best regards,
Kaja