topic PN7462 NFC Read card number problem in NFC

PN7462 NFC Read card number problem

steven123456 — Thu, 25 Feb 2021 11:08:12 GMT

Hi, I use PN7462AUHN design a board and use UART interface.

The internal regulator (DVDD, PVDD_OUT) work normally. TVDD_IN(PIN34) use 5V external supply.

Antenna side (TX1 TX2) we according to NXP antenna design guide to matching. Output power is 14dbm but finally can't read card number. Firmware on PN7462 EVB can read card successfully.

I want to ask maybe what kind of problem will cause fail to read card number?

Attached is my antenna test result and VNA measured result.

Re: PN7462 NFC Read card number problem

Kan_Li — Fri, 26 Feb 2021 09:07:19 GMT

Hello Steven,

Thanks for the information! Looks like it is an antenna tuning issue, from VNA.png, the point 1 is a little bit far from the straight line across the smith chart, you should tune it right on this line, something like Fig 33 in AN11706. Please kindly refer to https://www.nxp.com/docs/en/application-note/AN11706.pdf for more details.

Hope that helps,

Have a great day,
Kan

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Re: PN7462 NFC Read card number problem

steven123456 — Fri, 26 Feb 2021 12:19:00 GMT

Hi Kan,

Thanks for your reply. And I want to ask other question about matching.

1.When i use VNA measure tx1 and tx2 impedance, should I soldering the main chip and other components (about Rx and ANT components) on the broad?

Or use empty PCB board just soldering TX1, TX2 matching components?

2. I read NXP document AN11755, in this document mention symmetrical and asymmetrical tuning, should PN7462 use symmetrical tuning in AN11755? Or must same as AN11706 tuning method?

Best regards.

@Kan_Li

Re: PN7462 NFC Read card number problem

Kan_Li — Wed, 03 Mar 2021 08:20:20 GMT

Hi @steven123456 ,

1.When i use VNA measure tx1 and tx2 impedance, should I soldering the main chip and other components (about Rx and ANT components) on the broad?

Or use empty PCB board just soldering TX1, TX2 matching components?

- It is ok to leave the main chip and other components (about Rx and ANT components) on the broad when you use VNA measure tx1 and tx2 impedance. just note no power supply during the measurement.

2. I read NXP document AN11755, in this document mention symmetrical and asymmetrical tuning, should PN7462 use symmetrical tuning in AN11755? Or must same as AN11706 tuning method?

- Normally both methods can be applied for PN7462, but if you enable DPC, symmetrical tuning is recommended, please kindly refer to section 2.2 in https://www.nxp.com/docs/en/application-note/AN11741.pdf for more details. and yes, please use AN11706 for antenna design based on PN7462.

Have a great day,
Kan