What is the Zchip value of a ST25R3916B-AQWT chip?

[pablog]

Hello,

What is the Zchip value of a ST25R3916B-AQWT chip?

Looking at the AN5276 page 29, the Qucs settings for Zchip is 3Ω and Zchiphalf of 1.5Ω.  Should I use this same value for simulating the ST25R3916B-AQWT chip?  The other app note AN4974 says it is applicable for ST25R391X parts and on Page 46 it recommends a Zchip value between 14Ω and 20Ω.

What is the real NFC input impedance value of the ST25R3916B-AQWT chip?
What value of Zchip should I use on the Qucs simulation?


Thank you,
Pablo

[Travis Palmer]

Hello Pablo,

Zchip in the simulation is used to represent the driver resistance. 

It (Zchip half) is stated in the datasheet DS13541 Rev 8, page 148/165, table 127, parameter "Rrfo".

Since it is a differential driver stage, the RFO resistance is only half the driver resistance.

AN4974 is the antenna matching application note for the ST25R3911B. For ST25R3916B devices AN5276 should be used. On page 46 (AN4974 Rev 3) there is only the disclaimer.

But I assume you are talking about the Target matching impedance. This is the impedance which is connected to the RFO pins. Together with the supply voltage it determines the power consumption. 

A too low target matching impedance will cause a too high power consumption and violates the limits mentioned in the datasheet. The antenna matching application note should mention more details about the target matching impedance.

br Travis

[pablog · Accepted solution]

Yes, I was looking for the target impedance.  In this case, I will use the typical values of 3.4Ω for Zchip and 1.7Ω for Zchiphalf.

Thank you for your answer.