NFC PN5180 Antenna Sensitivity Problem

[emmanuel_sanche]

Hi,

I have a custom board with the PN5180 and I'm using it to emulate an NFC tag. I am able to read the tag with a phone at a distance of about 2.5cm, but after doing this once or twice, the antenna sensitivity seems to drop really low and I have to move the phone really close to the antenna (about 1mm distance between antenna and phone).

I noticed that I can reset the PN5180 and this will bring the range back up to 2.5cm, but again, it will fall to 1mm after scanning the tag once.

I have done the same test on the PN5180 development board (PNEV5180B) and I am consistently able to read the tag from a distance of about 3cm (no sensitivity issues).

Any Ideas?

Is the PN5180 automatically adjusting sensitivity? Do I need to change the value of NFCLD_SENSITIVITY_VAL in the PN5180 EEPROM??

Thank you!

[emmanuel_sanche · Accepted solution]

The problem were the AGC resistors on the RXP and RXN pins. Lowering their values from 4.7k to 3k fixed the issue.

[emmanuel_sanche]

Thank you for the response.

Yes, they both run the same software. I do think it is likely a hardware issue and I would appreciate a little guidance. 

I believe the custom antenna is not the problem because when I connect it to the PNEV5180B dev board, it works fine always.

I think the antenna matching circuit may be the culprit on the custom board, but the schematic was copied from the PNEV5180B datasheet. Maybe the PCB layout is the issue?

The part that has me confused is why the sensitivity is good at first, but then drops after a few reads with the phone.

Could it be that the Automatic Gain Control on the PN5180 is changing the 'sensitivity' because of a bad antenna tuning circuit??

Thank you for any advice!

Regards,

Emmanuel

[Kan_Li]

Yes, that is a possible cause, please refer to the following for more details.

NFC Antenna Design 

https://www.nxp.com/docs/en/application-note/AN11742.pdf 

https://www.nxp.com/docs/en/application-note/AN11741.pdf 

Hope that helps,

Have a great day,
Kan

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[Kan_Li]

Hello,

Did the same test on the PN5180 development board (PNEV5180B) run the same SW on your custom board? If yes, that might be a hardware design issue.

Have a great day,
Kan

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