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TRF7960: Question regarding operation if noise is induced on EN and/or EN2

Steve Bryant
Prodigy 90 points
Part Number: TRF7960
Other Parts Discussed in Thread: TRF7970A

Our design uses the TRF7960 in a RFID reader that is located near some high energy subsystems.  In our design EN and EN2 are tied to microcontroller GPIO lines.  EN2 is kept high and EN is toggled to turn RF on and off.  Occasionally the customer has reported that the RF field has turned off and they think it may be due to noise induced by the high energy system.  The question is if EN2 glitches down to 0 and back to 1, do we have to go back to EN=0, EN2=0 to get the device back into a known state?  Are there any constraints regarding the timing of this?

Thanks.

Steve

  • 0
    TI__Guru*** 135355 points
    Hello Steve,

    We haven't characterized the behavior of the device if EN2 has a small glitch like that. If issues are being observed due to it though, I think it's reasonable to think that something may have been affected inside the device as a result. Bringing both lines to 0 would be able to bring the device to a known state.

    We haven't had to apply time constraints for EN/EN2 on the TRF7960, though simple logic would suggest that the pins should transition cleanly from high to low logic levels (1V threshold). If it's unknown how brief that glitch is or what the voltage levels the glitch drops the line to are, then it would be good to be safe and reset the device by dropping both lines low. Keep in mind there is a 10-20ms set up time after the device is brought up from power down mode.

    For a later and more complex device (TRF7970A) we do have some constraints with the sequence of EN/EN2. If you wanted to be extra sure on the startup, you could use those? They are documented in Figure 6-3 and 6-4 of the TRF7970A Datasheet: www.ti.com/.../trf7970a.pdf
  • 0
    Prodigy 90 points
    Thank you Ralph. We're going to look into this further but your answer helps us for now. Steve.