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TRF7970 not operate on 5V.

Ravi Chaudhari
Prodigy 80 points


Hi 

We are working on TRF7970 in our new design for NFT tag detection. Our design is working on 3.3V but if we change Vin voltage 5.0V than we don't detect NFC tag. We measured voltage at antenna end at 5V is 20V peak-peak. We also implementing software as per errata and datasheet.

Please advice for ...

Regards,

Ravi Chaudhari.

  • 0
    TI__Guru* 91206 points
    Ravi -
    please ensure that you are writing a 0x21 to the Chip Status Control register (0x00) after applying +5VDC.
    i took a look at your schematic that you emailed separately -

    here is what i see:
    based on your schematic, you may be applying 5VDC to the MSP430, too. better check that.
    you need 2.2uF and 0.01uF on VDD_X
    ASK/OOK and MOD need 1k pulldowns mounted
    I/O voltage you have on VDD_I/O, I/O_1 and I/O_2 may also be set at 5VDC if you did not disconnect it - this would then mean that the MSP430 I/O
    has also would then have voltage mismatch. maybe better to connect to VDD_X, that is what that regulator is for really.

    then i see that you have series 33pF going into your RF switch - those will disturb the 50 ohm match unless you are using those as your series cap for matching the coil and you have the Q killer and resonance C out with the coil - that is not a normal topology, but electrically it would work i think.
  • 0 in reply to Josh Wyatt
    Prodigy 80 points

    Hi Josh,

    Thanks for reply.

    Controller MSP430 is operate on 3.3VDC not on 5VDC.   VCC3V_MP is mention in schematic as a in put voltage of micro controller. So VDD_I/O,I/O_1 andI/O_2 is also .3.3VDC.

    In our design we don't use internal regulator,than we open VDD_X pin as a test point. We will implement your suggestion and revert you back.

    Here I have some observation. Kindly suggest.....

    When we applying 5VDC at VIn of TRF , we get 20V peak to peak at antenna end(feeding point), and when we allpying 3.3VDC at VINof TRF, we get 16V peak to peak at antenna end(feeding point). Is it correct power output or not?

    Is tuning circuit  effected if we change input voltage? or tuning circuit will same..

    Regards,

    Ravi Chaudhari

  • 0 in reply to Ravi Chaudhari
    TI__Guru* 91206 points

    please have a look through the signal chain and see if these waveforms are appearing, first with your antenna disconnected at 50 Ohm point - if they are distorted, component check or layout check is in order, your schematic looked correct. then you can connect to your antenna

    if the antenna is tuned correctly, when running at 5V and 200mW you should see about 9-10Vpp (this is slide labeled 50Ohm Impedance Match Point) - depending on your antenna tuning and Q - you will see a higher or lower voltage here and a proportionally larger voltage on the coil itself. 

    also, you can use a scope and do math - if you have a power meter or spectrum analyzer with a power meter function - you can also check the TRF output with those. 

    (the next slide after 50Ohm Impedance Match Point shows using spec analyzer to look at fundamental and second harmonic)

    0564.TRF79xxA_Test points_05_2013.pdf

  • 0 in reply to Josh Wyatt
    Prodigy 80 points

    Hi Josh,

    We go thru your inputs and we are able to detecting NFC tag on 5V. We are getting 16V peak to peak at antenna end if we use 25mmX15mm size standard antenna(ANFCA-2515-A02). IF we use PCB antenna we get 12V peak to peak and get high detection range.

    We assume that due to reflection in standard antenna we get high voltage and poor detection. 

    How can I reduce reflection voltage and improve detection length? By using filter circuit ,can we get result? if you have filter circuit simulation tool or value please suggest to us. 

    Thanks for support.

    Regards,

    Ravi Chaudhari

  • 0 in reply to Ravi Chaudhari
    TI__Guru* 91206 points
    do you have access to network analyzer?