Ambiguous ST25DV-I2C StMicro literature.

[JohnSheley]

The last few lines of  StMicro’s ST25DV-I2C  low power application note (high lighted) are ambiguous. Does “ST25DV-I2C” have the ability to read/write EEPROM without power applied between pins VDCG and GND? (YES/NO) 

 Our desired application needs to read/write EEPROM via RFID when microcontroller's battery is dead. 

 StMicro Literature (see attached *.pdf)

Ultra-low power state

To save power, the ST25DV-I2C is completely shut down most of the time. In that state, the GPIO connected to

ST25DV-I2C’s VCC pin can be either forced to low-level output, in high impedance mode. The GPIO connected to

the ST25DV-I2C’s LPD pin can be in any state, high or low output, or high impedance without any influence on

power consumption.

If the ST25DV-I2C is powered by the RF field, it can receive and answer from any RF command and can send

an interrupt signal on its GPO pin to the microcontroller. The VDCG pin needs to be permanently powered. I2C

communication is not working. In that state, the ST25DV-I2C power consumption is null.

The figure below shows the ultra-low power state.

[JL. Lebon]

Hello, 

The VDCG pin is powering ONLY the GPO pin output buffer.

It is not mandatory for RF communication or for I2C communication.

It is mandatory only for the GPO pin to output the interrupt pulse signal.

You are right: the sentence "The VDCG pin needs to be permanently powered" is actually ambiguous.

VDGC needs to be permanently powered if you want the interrupt signal to work (e.g. to signal to the microcontroller that you want the VCC power back, or simply that there is RF activity). If you don't need the interrupt signal, you can tie the VDGC pin to ground.

Nevertheless, keeping the power on VDCG pin is not a problem in term of power consumption, as there is current draw only if the interrupt signal is toggling.

Best regards.