ST25R3916B power supply configuration

[steave_bhim]

Hi Community,

I am designing an NFC card reader using a combination of the ST25R3916B NFC frontend and the STM32L476 MCU.

The ST25R3916B has four supply input pins:

1. VDD_IO (pin 1): Connected to 3.3V for all serial communication.
2. VDD_A (pin 7): Typically connected to 5V by default from the booster.
3. VDD_RF (pin 9): Also typically connected to 5V by default from the booster.
4. VDD_TX (pin 10): Typically connected to 5V by default from the booster.

In my setup, VDD_IO is powered by a 3.3V supply, while VDD_A, VDD_RF, and VDD_TX are powered by a 5V booster supply, as seen in the ST25R3916B-EMVCO reference schematic.

My question is: Is it okay or recommended to supply these three pins (VDD_A, VDD_RF, and VDD_TX) with 5V? I originally planned to power everything with a single 3.3V supply, but I noticed in the reference schematic that they are supplied with 5V. Would it make any difference if I powered these three pins with 3.3V instead of 5V? Reducing the number of supply voltages by using a 3.3V supply would make the design cheaper and eliminate the need for a booster IC, but would this negatively impact the NFC TX and RX performance?

Regards,

SB

[Ulysses HERNIOSUS]

Hi SB,

please read DS chapter 4.2.10:

VDD_A is not to be supplied externally!

Putting VDD=VDD_TX=3V3 will reduce the achievable output power.

BR, Ulysses

[steave_bhim]

Hi Ulysses,

 

Thanks for letting me know.

 

In the reference schematic, they have used a 5V supply for VDD and VDD_TX, while VDD_IO is powered at 3.3V for serial communication with the STM32L4.

 

I have one more question. They provided me with the schematic design of the reference board, but not the Altium design files.

 

If I want to use the same NFC antenna as the development board, how can I do that? Could you guide me on this? If the design files were available, I could replicate the same traces directly.

 

Best regards,

SB

[Ulysses HERNIOSUS]

Hi SB,

which reference design are you looking at?

Previous post here: steval-st25r3916b-reader-expansion-board-circuit-schematic has Altium files...

BR, Ulysses