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TRF7970A Digital Input Voltage Range

Mark Williams
Intellectual 510 points
Other Parts Discussed in Thread: TRF7970A

Hi,

I am hoping someone can help me with my TRF7970A design. I can't find anywhere in the datasheet where it mentions the maximum digital input voltage.

The VDDIO pin can be used to set the digital output voltage range and input VIH and VIL thresholds proportional to VDDIO.

In my design the TRF7970A powers VDDIO from its VDDX output, derived from the 5V VIN supply.

My microcontroller is powered from a seperate supply at 3.3V and can take up to 5.5V on its inputs unpowered, so if the TRF7970A was to assert an output before the microcontroller supply is up then it is ok.

Going the other way, if the microcontroller were to assert a logic high before VDDX comes up I need to make sure the TRF7970A input will survive.

Do the TRF7970A inputs have input clamp diodes to VDDIO? Can they tolerate in input voltage independent of VDDIO or does VDDIO need to be up before any signals are applied?

For some reason I can't seem to find the input voltage range in the datasheet, just the high/low threshold voltages. Also VIH is listed as a max which seems a mistake as usually VIH threshold is listed in the MIN column, i.e. to be logic high the threshold needs to be 0.8VDD minimum.

Thanks in advance, Mark

  • 0
    TI__Mastermind 38620 points

    Hi Mark,

    Sorry this is not included in the datasheet.  We are checking on this with the designers and will have an answer for you shortly.

  • 0 in reply to Eddie LaCost
    Intellectual 510 points

    Hi Eddie,

    Any news on that input voltage range? If I can't get an answer I may need to add external buffering between the microcontroller and TRF7970A but this is a cost concious design so I would prefer not to add parts if possible.

    My main concern is the microcontroller asserting a GPIO pin high before VDDX is up and damaging the input of the TRF7970A.

    Thanks, Mark

  • 0 in reply to Mark Williams
    TI__Mastermind 38620 points

    Mark,

    I apologize for the delayed response.  I did finally receive some information.

    The output buffer is supplied by VDD_I/O with one diode from the I/O pin to VDD_I/O, so anything higher than VDD_I/O + diode drop is a problem.  If VDD_I/O is 0V, I would not suggest anything higher than ~650mV on the I/O pins. 

    Based on your circuit description, you will need to add buffering.     

  • 0 in reply to Eddie LaCost
    Prodigy 10 points

    Eddie,

    This is a very interesting data. Thanks.

    If Vdd_i/o is connected to another  (NOT Vdd_x) supply line  which remains always on, and the TRF7970A is powered down (EN & EN2 pulled down) : do the TRF7970A consume current via Vdd_i/o or are the internal buffers and level converters powered down ?

    Thanks,

    Arnaud