NTH1101: power consumtion of i2c; write data to which address?

[sandrogaehler]

Hi

I'm planning to build a small wireless sensor, which should be equipped with an active NFC chip for simple pairing.

What it needs to do:

• Wake up the MCU when the tag is read
• exchange some data with our smartphone app to check for authentification
• probably change some settings of the NFC tag during manufacturing of the sensor

Now I had a look at the NT3H1101, which looks just like what I need, but I have a few questions:

• There is an external power supply (Vcc) for the I2C interface. Is this enough to read and write configuration data to the chip, or does it need an NFC energy field for that?
• What is the power consumption of the Vcc line, if the chip is idle (no NFC field, no I2C communication)?
• I see that there is a flag when new data was written over one interface and is ready to be read by the other. How does the application know the #address of this data? Is there a standard for that, or do I have to come up with my own implementation in the application layer?

Kind regards,

--Sandro

[sandrogaehler]

Hi Jorge

Thanks for your reply. So we are aiming at <10 uA idle current consumption with our sensor, so I'm sorry to tell you that this chip won't do. Are there any chips available that are actually low-power and still connected?

Kind regards,

--Sandro

[Jorge_Gonzalez]

Hi Sandro,

To reduce the current consumption you could use a Power Management Unit (PMU) and enable power for the NTAG I2C only when a NFC field is detected (via FD pin) or when required from the I2C side.

Regards!

Jorge Gonzalez

[sandrogaehler]

Hi Jorge

So the FD pin also works if there is no power supply? There is no typical application circuit given in the data sheet, but I assume it needs a pull-up? What is the leakage into the FD and I2C pins in this case? (I found the 155 uA meanwhile, but the leakage is not given.)

Regards,

--Sandro

[Jorge_Gonzalez]

Hi Sandro,

Yes, the FD pin is operational without the power supply.

When not connecting VCC but pulling high the pins FD/SCL/SDA, the leakage current depends on the external voltage and the resistor chosen, but it should be less than 1 uA.

Regards!

Jorge Gonzalez

[Jorge_Gonzalez · Accepted solution]

Hello Sandro Gaehler,

Thank you for using the NFC community.

Regarding your doubts about NTAG I2C:

• There is an external power supply (Vcc) for the i2c interface. Is this enough to read and write configuration data to the chip, or does it need an NFC energy field for that?

Yes, the VCC is enough to read and write configuration registers or user data to/from the NTAG I2C chip. The NFC field is not required in this case.

• What is the power consumption of the Vcc line, if the chip is idle (no NFC field, no I2C communication)?

In "Idle state", the current consumpttion is approximately 155 uA.

• I see that there is a flag when new data was written over one interface and is ready to be read by the other. How does the application know the address of this data? Is there a standard for that, or do I have to come up with my own implementation in the application layer?

I guess you mean the flags SRAM_RF_READY and SRAM_I2C_READY. These flags are used in the Pass-through mode. The SRAM is a 64-byte space which can be used to transfer data between the MCU and an external NFC Host. The corresponding flag is set when the last page of the SRAM memory is written either by NFC or I2C side. For NT3H1101 in Pass-through mode the SRAM address from I2C side is (F8h to FBh) and for NFC side (F0h to FFh). The use of the SRAM memory space and the handling of the flags depends indeed of your application.

I hope this information helps.

Best Regards!,
Jorge Gonzalez

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