PN5190 Target Current for custom Antenna

[brunosc]

Context

I'm developing an NFC System based on PN5190 and NTAG NT3H2211. The tag antenna is very small (5mm diameter) and hence the reader antenna is also using custom dimensions. We have multiple designs for the reader antenna but for simplicity let's focus on the available standard Class-6 antenna design implemented on an FR4 PCB.

To maximize reading distance we opted for the PN5190 as it features the highest output power of all NFC frontends. Accordingly, the antenna (L = 2.1 uH) was matched acc. AN12549 with the low impedance of 16.6 Ohm (14.8 Ohm - j 7.5Ohm). Thus, the PN5190 should easily be able to drive a target current of 300mA.

We use the PN5190 evaluation board in the default configuration (internal DCDC, supplied by lab power supply for enough power) together with the NFC Cockpit. Protocol is ISO 14443A at 106 kbit/s.

Issue

As a first step I tried to calibrate the DPC to set the target current at 300 mA and enable appropriate power reduction following NXP guides (while DPC is off, EEPROM cleared).

However, the unloaded Class-6 antenna (as well as other custom antennas) exhibits a ITVVD of only 160mA (as read from the NFC Cockpit), which is much lower than expected.

DPC can be adjusted below the 160mA, but it cannot be increased.

Question

Why does the PN5190 system together with a 16.6 Ohm impedance Class-6 antenna drive such a low ITVDD? What part of the system can be adjusted to increase the ITVDD?

Background Assertions

I checked the TX supply, which is fine. The whole system works as expected when using the included Triton 45x45mm antenna (12.8 + j 13.4 Ohm; = 18.5 Ohm 46.3°), where it drives 300mA with no problems and the antenna + matching impedance with 18.5 Ohm is very similar to our custom antenna. If anything, driving a smaller impedance should only increase the ITVDD.

See attached antenna matching VNA results (measured from PN5190 160nH inductor EMV Filter) for appropriate antenna tuning reference.

[brunosc]

Hello @EduardoZamora , thanks for your valued support!

Component Values

Antenna: Class-6 acc. AN11276, measured to be L = 2.1 uH, R=2.3 Ohm

Chosen values as adapted by VNA and yes, following PN5190 antenna design guide, Chapter 4.4:

L0 = 160 nH, C0 = 560pF, C1 = 39pF, C2 = 97pF, Rs = 3.07 Ohm

The PCB layout definitely has an effect with its parasitic impedances, as the adjusted values (especially for C0) deviate quite a lot from the calculated initial values using AN12549 ( PN5190 antenna design guide, Chapter 4.2), which were:

L0 = 160 nH, C0 = 780 pF, C1 = 52.6 pF, C2 = 80pF, Rs = 3.07 Ohm.

Since the smith diagram looks right, I'm assuming the antenna tuning is fine.

DPC Calibration

Yes I checked the DPC calibration training you mentioned, but I was mainly following the more recent Online Training . In your video a correlation check is mentioned. But current documents and NFC Cockpit version 8.0.0 do not seem to document or support such a check. But this should not be a problem since L0 = 160 nH < 0.5*L_antenna = 0.5 * 2.1 uH.

My issue is not with DPC calibration itself, this is a future step. I'm confused as to why the ITVDD is reported to be much lower than the set target current while DPC is disabled and VDDPA is set to the 5.7V. See NFC Cockpit screenshot.

Is there a way to measure ITVDD directly on the PNEV5190 eval board?

[EduardoZamora]

Hi,

The difference in the selected components is significant. I tried to simulate your antenna, and these were my results:

• L0 = 160 nH, C0 = 780 pF, C1 = 52.6 pF, C2 = 80pF, Rs = 3.07 Ohm
   

• L0 = 160 nH, C0 = 560pF, C1 = 39pF, C2 = 97pF, Rs = 3.07 Ohm

The loading and detuning caused by PICC coming closer to the PCD antenna may affect the driver current ITVDD. What is the device you are approaching to the reader? By any chance, have you tested, for example, approaching a mobile phone to observe the behavior of the current?

Perhaps you could J8 from PN5190 eval board to measure the current consumption of the TX driver circuit.

All the default settings of DPC itself are made for the operation of the NXP PN5190 evaluation board PNEV5190BP. Other antennas normally require a proper DPC calibration according to PN5190 antenna design guide to achieve an optimum performance. The DPC calibration procedure requires to disable the DPC, which shall be done via EEPROM, followed by Soft Reset of the PN5190. Otherwise, the VDDPA and ITVDD might not show up as expected.

Regards,
Eduardo.

[brunosc]

Hi @EduardoZamora ,

Yes, the difference in selected components is significant, but the target impedance is met and smith chart looks appropriate. So I don't see an issue here.

What I describe is the behavior when the reader antenna is UNLOADED. When approaching a Class-6 antenna (from NTAG evaluation board) as a TAG, the loading indeed causes the ITVDD current to increase. But my issue is that ITVDD is 160mA when I select a target current of 300mA in UNLOADED situation.

Thank you. I could confirm that the NFC Cockpit ITVDD current correlates to the actual current measured in hardware.

DPC Calibration: Because I select a target current that is not reached (unless significant loading detunes the antenna at low distances), I cannot conclude the DPC calibration. See the following error:

Still, my issue remains that the actual ITVDD does not reach the selected target current, although antenna is properly tuned to 16 Ohm impedance.

[EduardoZamora]

Hi,

Could you please kindly clarify why this antenna size would be required for your design? Although there are many other factors involved, perhaps the antenna size you mention you are using may be a bit small for the application/requirements, and for this reason you are able to see that 45x45mm antenna provides a behavior closer to the expected.

By any chance, do you have any other larger custom antenna on hand that you could use for the test?

Regards,
Eduardo.

[EduardoZamora]

Hello @brunosc

Hope you are doing well.

In order to maximize the power transfer, a proper impedance matching is required. Your Smith Chart looks good; however, just to double check, could you please share the actual component values you are using for your antenna?

Also, could you please confirm that you have referred PN5190 antenna design guide, Chapter 3 PN5190 antenna requirements? Besides the circuitry you should consider for your antenna, some tips for your layout are shown here.

By any chance, have you checked PN5180 DPC Calibration | NXP Semiconductors online training? This video shows how to execute the calibration for the Dynamic Power Control (DPC) by using PN5180 DPC as reference and together with NFC Cockpit.

Regards,
Eduardo.