Hello,
There is tow ways of activating EH in ST25DV: EH enable after boot or EH enabled on-demand.
EH enabled after boot means that EH is enabled as soon as RF field is strong enough.
EH enabled on-demand means that you need to enable it manually by writing a dynamic register each time you want to have EH.
EH on boot can be enabled by writing in the Static configuration register EH_MODE with value 0.
This can be done in Arduino with the ST25DV_i2c_WriteEHMode(ST25DV_EH_ACTIVE_AFTER_BOOT).
EH on demand can be set by writing a 1 in the dynamic register EH_CTRL_Dyn.
In Arduino, this is done with ST25DV_i2c_SetEHENMode_Dyn() and ST25DV_i2c_ResetEHENMode_Dyn().
Best regards.