ST25R3916B – XTI/XTO Pins, Crystal Requirement, and MCU_CLK Usage

[MERSI]

Hi everyone,

I'm currently working with the ST25R3916B NFC reader IC and I have a few questions regarding the XTI and XTO pins as well as the MCU_CLK output.

From the datasheet, I understand that:

• XTI is the input and XTO is the output of the internal crystal oscillator circuit.

• The oscillator is designed to operate with a 27.12 MHz external crystal.

Now, here’s what I’d like to confirm:

1. Is the external 27.12 MHz crystal absolutely required for normal operation, or is there an internal oscillator that can be used as a fallback?

2. Regarding the MCU_CLK output: this seems to be a clock signal derived from the oscillator.

   • Is this optional?

   • It is used to clock an external microcontroller (e.g. STM32)? Do I have to use it? Many STM32 MCUs already have decent internal oscillators.

3. Are there any recommended crystal components (specific part numbers or manufacturers) that are known to work well with this IC?

Any clarification or insights from those with experience using the ST25R3916B would be greatly appreciated!

Thanks in advance!