Skip to main content
R
REdmo.1
Visitor II
February 21, 2023
Solved

Energy Harvesting not available when RF is sleep or disabled

  • February 21, 2023
  • 11 replies
  • 6485 views

In the ST25DV data sheet, I read:

"Energy harvesting can be set even if ST25DVxxx is in RF disabled or RF Sleep mode, or in Low power mode. In all these cases, ST25DVxxx will deliver power on V_EH pin if RF field is present."

However this is not what I am seeing.

If energy is being harvested to power the MCU and it sets either RF_DISABLE or RF_SLEEP in RF_MNGT_Dyn via i2c ,the energy harvesting output disappears and the system dies.

Is this an error in the data sheet or is there a way to disable/delay enabling RF communications whilst maintaining Energy Harvesting?

I suppose that the possibility exists that the phone is switching off the field when RF communications are disabled, but this amounts to the same thing.

I want to be able to delay RF communications until the MCU has written the NDEF record to the EEPROM, i.e. I want to power up from harvested energy with RF communications initially disabled.

Thanks,

Richard

    This topic has been closed for replies.
    Best answer by JL. Lebon

    Hello Richard,

    I'm glad you made progress in your design.

    Concerning simultaneous access to the ST25DV, your solution of queueing the I2C writes looks clever.

    You have to consider also that an I2C write in the EEPROM memory does not end at the STOP bit, but when the programming in the EEPROM is really completed (programming starts at the STOP bit and duration is dependent of the number of Bytes that are programmed). The I2C is considered "busy" during this programming time and RF cannot access the ST25DV during this time, even if the I2C bus is free.

    This is all explained in (yet another :grinning_face:) application note: https://www.st.com/resource/en/application_note/an5624-how-to-manage-simultaneous-ic-and-rf-data-transfer-with-an-st25dvxxkc-device-stmicroelectronics.pdf

    This application note may help you to improve avoiding simultaneous accesses.

    Best regards.

    11 replies

    Show previous replies
    J
    JL. Lebon
    ST Employee
    March 16, 2023

    Hello Richard,

    Yes, the ST25DVxxKC has different GPO registers as it has more interruptions than the K version. This can be a trap, don't be embarrassed :grinning_face:

    I'm glad this solution works well. I think I will update the AN, adding this solution so that others can also benefit from this.

    Best regards.

    Terms & ConditionsAccessibility statement