NTAGI2C Questions

[MikeBrennan]

Have a project in prototype with the NT3H2XXX.  The chip is working, and we refine the application.  Two questions have surfaced, and I would appreciate some help getting answers.

1. What is the nominal value of the tuning capacitor for a Class 6 antenna?  ( We do not have the expertise to characterize the antenna. )
2. We have 10uF of bypass capacitance on the VCC in an energy harvesting application.  The application runs fine with it, but the data sheet recommendation is 0.22uF.  We are using a passthrough mode only and do not shut down the reader’s RF field as a part of operation.  Is the 10uF of bypass capacitance okay?

[Jorge_Gonzalez]

Hello Michael,

Some information about your questions:

1) There is not a nominal value, actually the external capacitor would not be required in a well-tuned antenna. If you are not sure about the tuning then you can place a small capacitor in the range of 14 pF - 100 pF and make some tests to obtain optimum performance, but ideally it should then be removed to add coil turns and increase inductance. The antenna design guide ZIP package has excel sheets to aim with the design and calculation of the antennas, including gerber files for Class 4, Class 5 and Class 6 antennas:

http://www.nxp.com/documents/application_note/AN11276.zip 

2) I guess you mean a capacitor in the Vout pin and use energy harvesting feature to power VCC. I think it would be ok to use the 10 uF, but you need to consider the capacitor charging time, which would be a few ms. The application needs to wait for VCC to stabilize before talking to the NT3H2XXX via the I2C bus.

I hope this helps.

Regards!

Jorge Gonzalez