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PN532 LOADMOD implementation

Question asked by Ivan Dodig on Jan 21, 2017
Latest reply on Feb 13, 2017 by Jorge_Gonzalez

Dear NXP,

on our custom PN532 board we noticed that LOADMOD network is detuning the antenna when 1k resistors are placed.

When we remove them, the range doubles. 

We suspect that this is due to our NFET selection.

BSS138 have 13pF of output capacitance and this in series with 1kR introduces losses to the antenna? 

 

Would lower capacitance FETs solve this issue? Can you recommend us a SOT-23 capacitors specifically for LOADMOD circuit?

 

Also, can you confirm that LOADMOD circuit is needed for card emulation? We saw on few places that the IC can do card emulation without it, is this true?

 

The best solution for us is to remove the LOADMOD circuit altogether if it's not needed.

 

Thank you for your help.

Ivan

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