PN5180 receiver coupling resistor optimization

[t-a-r]

Hi all,

We are looking for some more information about how best to determine the values ​​​​for the coupling resistors for the receiver inputs for the PN5180.

Is there more detailed information on a procedure or how to best use the software library functions to use to perform this test?

This is only briefly described in the datasheets. In PN5180A0XX-C1-C2 data sheet section 11.8.9(.2) it describes the AGC functions and that the PN5180 will attempt to auto-range the RXP signal to be 1.5 to 1.65V by adjusting internal resistance as a 10-bit value against the user defined external coupling resistor(s). The external resistors are mentioned as being up to 10K ohms. We used the 4.7K ohm resistors that were on the evaluation board/reference design. Now we want to confirm that the 4.7K ohm values ​​​​are optimal.

AN11740 section 4.5 has some mention of this but is not sufficient for us to understand what specifically to do in software. Section 4.5.1 says to " Apply the default AGC settings, eg with the default LOAD_RF_CONFIG for type
A@106, ensure the gear 0 is used (if DPC is enabled), ensure that the antenna is not
loaded and switch on the carrier"

We are not using DPC, so, do we need to define a gear? If so, how is this done?

Is switching on the carrier done by the RF_ON command?

We are using the older v3.4 FW in the PN5180. We are not using DPC, device is used in reader mode only and we are only reading ISO14443 type A cards.

Thanks.

[t-a-r]

For the sake of closure, we ended up getting a PN5180EVAL board and changing all the matching components on the board to be the same as our custom PCB.  We used the same PN5180EVAL antenna but we could have removed it and connected to our board antenna trace.  This allowed us to test various damping resistors and see how it changed the AGC_VALUE.  We observed similar values for AGC_VALUE to what we had seen on our custom board and software. 

The result is that our values of 0x035 to 0x045 were much lower than ideal and we changed damping resistors from 4.7K to about 2K to move the receiver signal more to optimum range.

We note that PN5180EVAL wants to use the newer v4.0 FW of PN5180 and we want to use the older firmware v3.4.  Therefore, the evaluation platform is not ideal for debug of older designs.

[t-a-r]

Follow-up: we were able to confirm that the RF carrier is continuous on by using an oscilloscope and current loop probe.  When reading the RF_STATUS register we see values typical of about 0x00F60039.  The AGC_VALUE is the lower 10 bits and these seem to range from about 0x035 to maybe 0x045.

Is there more detailed information about how to determine the coupling resistor values than in the two resources I mentioned?  Perhaps for another similar device?