How to protect NFC readers chip (ST25R3920B) when co-working with Qi wireless charger?

[Aplemay]

my application is NFC readers (ST25R3920B) polls whether there is an approaching card. Qi wireless charger searching devices with analog/digital ping, and start Qi wireless charging if WC device is found.

I found the chips (ST25R3920B) is always broken after aprox. 1 hour searching. The issure is in working with Qi Wireless charger. What cause it? Is it cause by wrong setting (e.g. external field detector) ? How to protect the chips? How to protect NFC chip when co-working with Qi wireless charger? Is there any suggestion on hardware design and software desgin?

[Ulysses HERNIOSUS]

Hi,

in our experience NFC readers are not affected by Qi chargers. This is of course different for NFC tags.

I think for understanding the issue we will need to better understand your system: Used charger, used board, used antenna, antenna characteristics, etc. What is the symptom of the broken chips?

Please share such, potentially also in a private message.

BR, Ulysses

[Aplemay]

Hi Ulysses,

something more. not only NFC chip is broken, mcu is broken as well. it can be repeatable. After both ST25R3920B and mcu are replaced new chips, the system works again. MCU and nfc reader shares same 3.3v supply. I measured forward/reverse voltages of the internal diodes on SPI port, diodes seems no damage found.

BR​

[Aplemay]

Hi Ulysses,

the board intergrates Qi charger part and NFC reader part together. The coils/antenna used are independent. NFC antenna is PCB antenna. As the project is in the functional realization at present, antenna has not been matched. Matching component is installed according to default value in Matching Tool at present. No appearance after chips broken. But it has no response on SPI interface.

You mentioned it is different for NFC tags. may I know details?

BR​

[Travis Palmer · Accepted solution]

Hello Aplemay,

NFC is heavily used by automotive customers for paining in the center console and NFC card protection.

Automotive customers are very carefully testing their applications in all possible conditions. We are aware of various projects combining Qi Charger with ST25R39xx devices and so far we have not received such reports.

You should measure all possible supply voltages and connections to the NFC antenna (as well as AAT_A and AAT_B connections) during all possible states: power down, NFC active, Qi ping, Qi power transfer with several devices.

Compared to NFC tags, readers do have the mathing network between the antenna and IC. Tags typically have the antenna connected directly to the IC. This is why they are more exposed to the environment.

please feel free to share the outcome.

BR Travis