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Connecting NT3H22xx to external power

Question asked by John Logan on Nov 4, 2016
Latest reply on Nov 9, 2016 by John Logan

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?