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Standalone ST25DV64K

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LAmar
Associate II

‎2019-02-06 05:51 PM

I wonder if a ST25DV64K can be used in standalone.

If I connect AC0 and AC1 to an antenna (using a smartag antenna), shouldn't the Harvest (V_EH) pin potential be around 3.3V (compared to the GND).

Does the EEPROM configured to provide this power voltage by default?

Thanks

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JL. Lebon
ST Employee

‎2019-02-07 01:27 AM

​Dear Leo,

Thank you for using ST25DV64K.

Yes, the ST25DV64K can be used in standalone, no problem.

It just needs to be connected by Ac0/Ac1 to an antenna.

When a NFC reader (or smartphone with NFC) is placed close to the antenna, the tag is powered by the RF field through the AC0/Ac1 pins, and is functional.

No need to VCC power. Off course, I2C is not working in this configuration.

Concerning energy harvesting, it is functional if you have RF field power on AC0/AC1.

EH is not enabled by default. You need to configure it with an RF reader or smartphone.

There is two choice:

  • configure it to automatically deliver power as soon as RF field is present (and powerful enough). For this you should write a 0 in the EH_MODE static register, using the Write Configuration command at address 02h.
  • configure it to deliver power "on-demand": for this you should write a 1 in the EH_CTRL_Dyn register, using the Write Dynamic Configuration command at address 02h. The power is delivered only once this bit is written, and on next boot, you will have to do it again as this register is volatile.

I recommend the second method.

Once RF field is present and EH is enabled, the St25DV can deliver 3.3V between V_EH pin and Vss pin. The exact voltage depends on RF field power. It is not regulated and can vary around the 3.3V (up to ~4V and down to ~2V), so you may want protect your external device if it doesn't not support more than 3.3V (i.e. by adding a 3.3V Zener diode to limit).

Hope this answers your question.

Best regards.

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JL. Lebon
ST Employee

‎2019-02-07 01:27 AM

​Dear Leo,

Thank you for using ST25DV64K.

Yes, the ST25DV64K can be used in standalone, no problem.

It just needs to be connected by Ac0/Ac1 to an antenna.

When a NFC reader (or smartphone with NFC) is placed close to the antenna, the tag is powered by the RF field through the AC0/Ac1 pins, and is functional.

No need to VCC power. Off course, I2C is not working in this configuration.

Concerning energy harvesting, it is functional if you have RF field power on AC0/AC1.

EH is not enabled by default. You need to configure it with an RF reader or smartphone.

There is two choice:

  • configure it to automatically deliver power as soon as RF field is present (and powerful enough). For this you should write a 0 in the EH_MODE static register, using the Write Configuration command at address 02h.
  • configure it to deliver power "on-demand": for this you should write a 1 in the EH_CTRL_Dyn register, using the Write Dynamic Configuration command at address 02h. The power is delivered only once this bit is written, and on next boot, you will have to do it again as this register is volatile.

I recommend the second method.

Once RF field is present and EH is enabled, the St25DV can deliver 3.3V between V_EH pin and Vss pin. The exact voltage depends on RF field power. It is not regulated and can vary around the 3.3V (up to ~4V and down to ~2V), so you may want protect your external device if it doesn't not support more than 3.3V (i.e. by adding a 3.3V Zener diode to limit).

Hope this answers your question.

Best regards.

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