Javacard with ST33 SE, ST25 NFC Chip and ePaper Display (SPI) powered by NFC Energy Harvesting

[praveenbm5]

Hi

I am a complete beginner when it comes to Smart Cards/Javacards, Secure MCUs and NFC.

We specialize in Bitcoin/Crypto Custody and are exploring Smart Card (Javacard) based secure storage of end-user private-keys.

We want to design and manufacture a Javacard based Smartcard with ePaper display that shows details about the operation being performed on the Smartcard. And we want this smartcard to be a passive device without any battery just like normal smartcard. So the ePaper display has to be powered by the energy harvested from NFC.

After initial exploration, we found that we need to use ST33 Secure MCU connected to a ePaper display through SPI along with ST25DV-I2C NFC chip to enable the NFC interaction with Smartphones and harvest RF energy to power the MCU and display.

We want to do the exact same thing as described in Application Note - AN5233 with a ST33 Secure MCU instead of STM32 MCU. 

This is as far as we could get and do not know how to proceed further. Any help in this regard will be much appreciated. 

Thank you.

[Rene Lenerve]

Hi praveenbm5,

I cannot answer for the ST33 Secure MCU and you should contact the local sales for that product to get more information as this is not a public product.

Regarding the ePaper, the power required when updating the screen can be provided by the Energy Harvesting of the ST25DV, but in the example you are referring to, the use of a tank capacitor was necessary to provide the current peak required when fully updating the screen (peak which is brief but with a high current). Look at the characteristics of your ePaper to be sure that the Energy Harvesting will be sufficient to provide enough current for all modes.

For the ST25DV, there is an Application Note that give some information about the Energy Harvesting :

https://www.st.com/content/ccc/resource/technical/document/application_note/group0/c2/1f/83/75/2c/f1/41/78/DM00329035/files/DM00329035.pdf/jcr:content/translations/en.DM00329035.pdf 

For energy harvesting and smartphones, be aware that the energy harvested can vary a lot between phones, it depends on physical factors and NFC on smartphones can have various characteristics.

The current provided by the EH pin will power all the components :

- MCU (need to reduce at max the sysclock frequency and IPs used, low power if available).

- ST25DV (RF analog will be powered by the RF Field, but digital part needs VCC => V_EH).

- ePaper (check peak current in certain mode).

I hope this can help you a bit more.

Kind Regards.

[Ulysses HERNIOSUS]

Hi praveenbm5,

Smart cards / Java cards typically have ISO/IEC 14443 interfaces. Do you have a specific Application Protocol in mind which you have to fulfill? Or you want to define your own Application Protocol?

BR, Ulysses

[Rene Lenerve]

Hi Ulysses,

Thank you to pinpoint that smart cards / java cards are ISO/IEC 14443 interfaces, because ST25 tags with Energy Harvesting feature are only on ISO 15693 standard.

Kind Regards.

[praveenbm5]

Hi Rene

Thank you for the insightful reply. A tank capacitor will definately make the whole thing easier to accomplish.

I was also wondering how to embed a good sized capacitor in a smart card.

But have seen some smart cards with epaper displays (passively powered by NFC EH). I guess there are EDMs now that need very low peak power to update. Am already in touch with one such smart card manufacturer and they are reluctatnt to share more details 🙂

And not all smartphones with NFC will be compatible with cards with EDM. It will greatly depend on their internal NFC components, especially antenna size.

I was just wondering if I can replicate the setup shown in Application Note AN5233 with an ST33 instead of STM32 as a POC.

A strict adherance to smartcard physical size specification is not exactly critical to our use case. 

[praveenbm5]

Hello Ulysses

We are planning to write applets for Javacard framework for our usecase, so we will use standard interfaces and communication protocols.

[praveenbm5]

Thank you for pointing this out. Now I am not sure about which chips to use but our use case remains the same.

We are looking for a NFC enabled Javacard with ePaper display connected to the Secure MCU via SPI to show some information about the operation being performed and ideally the whole thing should be powered by energy harvested from NFC.

May be ST54 or ST31 can do the trick? Please suggest.