I uses MFRC630 reader chip and I'm facing an issue. I have followed all application notes and I'm able to fine tune my antenna (EMC, matching Circuit and Receiver circuit are perfectly adapated).
Once connected to the reader I observe some strange behaviours.
I configure Command register to 0x00 and DrvMode register to 0x8E, the most important information is that TxEn is set. I can see that a field is generated (2A/m) at 13,56MHz and if I use the software drivers I have found on internet I can see a REQA and even get the ATQA and UID.
BUT, for an unknown reason, sometimes the reader stops the transmitter, I have to reboot the reader to get it work again. The bit TxEn is cleared ('0') and even if I force this bit to '1' it has no effect. Even sometimes, the command (register 0x00) is forced to 0x40 (ModemOff -> power down).
Ex: I write 0x8E in DrvMode and read back 0x86 and no field is generated. Or even sometimes I write 0x00 in command register and read back 0x40
If I probe Tx1 or Tx2, I can see that it is flat to the Tvdd supply (3.3V), no oscillation is observed when it fails. However, If I isolate Tx1 and Tx2 from the matching circuit and antenna, it oscillates fine. I have the feeling that something in my circuit is disturbing the reader.
Last point, as I wanted more field, I have changed Tvdd from 3.3V to 5V (Vdd and Pvdd are set to 3.3V) and the transmitter never works in that case. Tx1 and Tx2 are flat to 5V.
Any idea what can cause this behaviour? I have some difficulties to fine tune my setup, the reader stops working all the time.