NFC WLC Reader to Reader Energy Harvesting

[Voxel]

I am creating a battery powered NFC Reader PCB that has an STM32L4 and some buttons and LEDs on board.

The main task should be to read passive NFC tags, but I also want to be able to charge the reader itself wirelessly via WLC. I read a lot of documentation of the ST25R and ST25D family of products, but I only found the use case of powering a ST25D Tag and use its energy harvesting capability to charge a battery.

My question is if there is an existing product that is able to read passive NFC cards as well as be charred via WLC? Or is a battery powered NFC reader a bad Idea to begin with. 

[Ulysses HERNIOSUS · Accepted solution]

Hi Voxel,

I think you are going where nobody has gone before. I have some doubts:

1. I am more on software and system level, but I am not sure if an antenna of a PTx is also good to act as PRx
2. A reader requires considerable output power so unless you are rarely using the reader function, it may not be possible to acquire enough energy to create an RF field to power tags.
3. There are always losses in transferring the power. If you have such a double use system I expect them to be even higher.

BR, Ulysses

[Voxel]

I am willing to trade efficiency for convenience. Having no extra port for charging the device increases the "IP Rating" greatly.
The main problem is, that I can't find anything in the documentation if the reader IC's are even capable of receiving power. The big problem is the negotiation of which device is the charger and who is being charged. Like USB-C PD, there needs to be communication beforehand.

[Schuyler]

Hi, @Voxel 

I want to know the case of powering a ST25D Tag and use its energy harvesting capability to charge a battery，but I couldn't find battery charging. Is there any relevant document about charging the battery with the energy of ST25 wireless charging?

Hope to get your reply!

[Voxel]

For a "standard" solution meaning the energy transfer from a reader to a tag, there is an official application note that goes into great detail about the whole topic

https://www.st.com/resource/en/application_note/an4913-energy-harvesting-delivery-impact-on-st25dvi2c-series-behaviour-during-rf-communication-stmicroelectronics.pdf

[Schuyler]

@Voxel 

OK, I noticed this document. But with an energy output of just a few milliwatts, how can it power L4? I'm a little confused about this