ST25R3916B reader design with external antenna

[Dilip]

Hi ST Team, 

I am new to NFC and have designed the schematic for NFC reader and antenna based on ST25R3916B. I am connecting these 2 PCBs with UFL connector antenna cable. When i started to test, some how it did not work, meaning tag is not detected. Can you pls review my design and suggest what changes should i do changes  in BOM to  have matching circuit and tune the antenna so that i can get the signals when tag is detected.

Below is are the schematic and PCB images attached here for review. I would appreciate if i get any reply at the earliest.

Since I am using antenna on a different PCBA, so I have used  reader in a single ended mode and used RFO1 and RFI1 for transmission and reception.

[Travis Palmer]

Hello Dilip,

The NFC reader schematic seems just to be a blank page.

From the Layout i noticed that the capacitive voltage divider is missing, please check this part of the schematic. 

From your description it is very hard to predict what is wrong with the device.

Can you please give a few more data points:

• Are all supply's as expected
• Is the power consumption in the specific modes as predicted in the ele. charac. table of the DS
• Is SPI communication ok.
• Is the oscillator swinging at 27.12MHz.
• please check the voltages at the RFO and RFI.
• Did you check the verification steps of AN5276 - chapter 7?
• Did you design the antenna in accordance to AN5592
• Can you provide a smith chart of the reader matching and the matching of the single ended antenna?

please let me know if you have further questions

BR Travis

[Dilip]

Hi Travis, 

Pls find snap shot schematic. I have checked voltage divider is there . Pls see below in snap shot

Pls find below answers for your queries

yes 3.3V is okay on all pins as expected

Yes power consumption as expected

I am using I2C which works well.

Yes I have designed the antenna and its matching circuit as per AN5592

I dont have network analyzer , so can not create smith chart. 

I just want you pls check my schematic for  antenna impedance matching network and tuning circuit on antenna PCBA.

Also can you pls help what register configurations I have to do for single ended mode with cable and detection of ISO15693 complied tag.

Thanks

Dilip

[Travis Palmer · Accepted solution]

Hello Dilip,

I have seen two things that need to be considered:

1. The connection of the capacitive voltage divider / antenna is incorrect:

For comparison the schematic stated in the AMT:

2. The decoupling pair at VDD_AM requires the chip to be operated in ST15R3916 mode.

Please have a look at AN6313, chapter 4 Device behavior after power-on and VDD_AM capacitor usage.

• It might be required to verify your smith chart using a VNA. 
• There are two bits in the IO Configuration register 1, which need to be set correctly:

BR Travis