topic Re: transmitters stop working in NFC

transmitters stop working

loichenninot — Sat, 02 Dec 2017 12:54:39 GMT

Hi,

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 :smileysad:

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.

Best Regards,

Loic

Re: transmitters stop working

Kan_Li — Thu, 14 Dec 2017 09:07:25 GMT

Hi Loic,

For the TX1 TX2 probing issue, looks like the antenna was not tuned well. Have you compared the simulation result with the measured result? You have to make sure they are almost the same before further tuning.

Hope that helps,

Best Regards,

Kan

Re: transmitters stop working

loichenninot — Thu, 14 Dec 2017 15:42:45 GMT

Hi Kan,

many thanks for your reply.

The measurement done with the VNA between TX1 and TX2 is quite similar to

the simulation. I'm pretty sure that my antenna is tuned correctly, not

perfectly but correctly. From my understanding, it should have an impact on

the communication but I'm not sure about stopping the transmitters.

Do you know what could be all the cases where the transmitters stop

working? I can see a start of field, as though the transmitters wanted to

generate a field but for an unknown reason cannot. When I read back the

DRVMODE register, the bit TxEn is always cleared '0' and Tx1 ant Tx2 have

the TVDD level.

What are the cases where the chip is in security and cannot uses

transmitters properly? too many current on TVDD? i'm not even able to

measure I(TVDD) because the transmitters are not working. I have changed

the reader chip and I have the same behaviour, something is wrong on my

design and I have no indications in the datasheet or application notes

about the potential error that could stop the transmitters to work.

I'm wondering if the PCB can have an impact on my issue. I have a 2 layers

PCB without vias under the heatsink pad.

Anyway, any clues on this would appreciate.

Best Regards

2017-12-14 10:08 GMT+01:00 Kan_Li <admin@community.nxp.com>:

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