PN532 LOADMOD implementation

[ivandodig]

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

[carl1]

We're having the same issue, would love to have an answer on this question.

[Jorge_Gonzalez]

Hello Ivan, Carl:

The LOADMOD active circuit is optional in card emulation mode. The load modulation signals can be generated by the transmitter via the TX1 and TX2. See the application diagram from the datasheet:

Best Regards!,
Jorge Gonzalez

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