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TRF7970A output levels

John Hite
Expert 1355 points
Other Parts Discussed in Thread: TRF7970A

My board runs on 3.3 volts and I am looking at the interrupt output pin of a TRF7970A on a scope. When there is no interrupt it is a solid low. However after sending the REQA sequence the output may be 1.5 volts or it may be 2.5 volts, sometimes it floats up and down a bit. The project EE can't find in the datasheet what the output type is tho I would assume totem pole.

Anyone know for sure?

Thanks,

jh

  • 0
    TI__Expert 3550 points

    Hello John,

    On the TRF7970A datasheet (SLOS743K) the Voltage range for pins are located on Section 5.2 (Recommended Operating Conditions). The logic low is less than (0.2 * VDD_I/O ), and the logic high is greater than (0.8 * VDD_I/O).

    A few questions to help replicate the issue that you are seeing:

    1. Are you currently using a TI platform with the TRF7970A or did you create your own PCB?

    a. If you are using a TI platform,can you comment on which pin you are measuring the voltage?

    b. If you created your own PCB, can you provide the schematics for the transceiver section?

    2. Are you able to get a response from a ISO14443-A tag when you send the REQA?

    3. If you were to read the IRQ Status register (0x0C) when the voltage increases, what value does it have?

    3. What software project (TI application note?) are you using to test your hardware ?

    Best regards,

    Erick M.

  • 0
    Expert 1355 points
    Erick,

    We are using our own board. Switched to a different board late yesterday that didn't have that problem. However this board and the other 3 have a problem with the oscillator circuit perhaps because our crystal has the typical 50 ohm impedance instead of 40. It is very hard to find a crystal with 40 ohm impedance with less than a 16 week wait time so tomorrow we will receive powered oscillators and put an end to that problem.

    Haven't gotten a tag response yet but the rf output from the chip was a series of bursts about 500 mv amplitude.

    Regarding software projects/app notes. I would be interested to see these.

    I'll report back on Tuesday about how this new board works with the new oscillator.

    Thanks,
    jh


  • 0 in reply to John Hite
    TI__Guru* 90906 points
    John -
    we have found anything under 100 Ohms ESR is working - just FYI -
    for example on the TRF7970AEVM, crystal used was from ECS: www.ecsxtal.com/.../csm_7.pdf (mfg part number: ECS-135.600-CD-0374, Digikey has stock)

    on the TRF79x0ATB ==> www.itti-co.com/.../id_44.pdf (from ITTI)

    on the TI Designs for UART (www.ti.com/.../TIDM-NFC-EZ430-MODULE) and I2C (www.ti.com/.../TIDM-NFC-I2C-MODULE) ==> www.txccrystal.com/.../7a.pdf (Mfg PN 7A-13.560MAAJ-T, Digikey has stock)