Connecting NT3H22xx to external power

[johnlogan]

Hi. We have an application where we will have an NT3H2211 connected to a microcontroller that is monitoring some sensors. All the examples seem to have the NFC IC providing power from the Vout pin to the controller and so there is no contention between the controller supply and the NFC internal supply. In our application we need to power the micro from a battery so that it will run when there is no field present. This is so it can continually monitor the sensors, log the data which is subsequently downloaded vis the NFC chip. We connected the device to the microcontroller with the VDD pin connected to the 4.4V microcontroller supply. The I2C pull ups are connected to the shared VCC line as is the FD pull up. We left the Vout pin floating as this is at 2.7V when a field is present and we are currently running the micro at 3.3V ( although eventually we will run it off a 3V lithium battery). I have attached a simplified schematic to see what we have done. With this set up we seem to have blown the I2C interface on two of the NFC chips so we are clearly doing something wrong. Should we tie Vout to the 3.3V supply? Is there a better choice of NFC chip if we do not need the energy harvesting function?

[johnlogan]

Hi Weidong

The schematic I attached to this support request shows that we are doing exactly as you suggest, i.e. attaching VCC to the 3.3V supply and floating Vout. However we have tried this out with two separate NFC tag antennas from the NTAG kit that have the NT3H2211 on board and BOTH devices have failed. The failure condition is that the device no longer responds to the I2C bus. I would like to understand why this happened before we try any further devices out as 100% of the parts we have done this to have failed. Can you suggest why the devices we have tried have failed?

Regards

John Logan

[weidong_sun]

Hello John,

>>Should we tie Vout to the 3.3V supply?

No, it is not necessary. floating Vout pin if you don't want to use it.

>>Is there a better choice of NFC chip if we do not need the energy harvesting function?

Your solution is no problem, don't need to get another choice.

Best Regards,

Weidong