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TRSF3223E: TRSF3223E

cannie chang
Intellectual 910 points
Part Number: TRSF3223E

Tool/software:

Hi, 

Here’s a refined version of your text with grammar corrections:

I have the following questions that need your help:

  1. When we change the RS232 input signal to below ±2.7V, the invalid signal does not toggle, and the output data is still correct.

  2. When we change the RS232 input signal to below ±0.66V, the invalid signal becomes low. The datasheet shows it should be below ±0.3V and remain there for 30μs.

  3. When the input signal is above ±1.5V, the invalid signal stops toggling, and the output data is correct. This does not match what is described in the datasheet.

  4. What is the meaning of Figure 5-3 in your datasheet (SLLS824B – AUGUST 2007 – REVISED DECEMBER 2023)? Does it mean that when the input signal is more than ±1.5V, it becomes valid?

Thanks

cannie

  • +1
    Guru 317370 points

    Voltages above ±2.7 V are guaranteed to be read as valid.
    Voltages below ±0.3 V are guaranteed to be read as invalid.
    For voltages between ±0.3 V and ±2.7 V, there is no guarantee.

    Figure 5-3 does not apply to the /INVALID detection. Figure 5-5 uses the correct thresholds.

  • +1 in reply to Clemens Ladisch
    Intellectual 910 points

    Hi,

    We checked that when the input signal is above ±1.5V, it becomes an output and Valid becomes high. In Figure 5-3, 1.5V is used as the reference point for tpd. Does this mean that an input signal greater than ±1.5V is acceptable?

    Br,

    cannie

  • +1 in reply to cannie chang
    Guru 317370 points

    ±3 V is the minimum valid RS-232 bus voltage. 1.5 V is just the midpoint between these two levels. (And it's wrong; the midpoint between −3 V and 3 V actually is 0 V.) The midpoint is used just for timing purposes. Figure 5-3 has nothing to do with the /INVALID output.

  • +1 in reply to cannie chang
    TI__Guru 73891 points

    Hi Cannie,

    Just parroting what Clemens has said (since he is correct). 

    Our datasheet essentially guarantees if you are between -0.3V and 0.3V for ~30uS then it will trigger the invalid output. But it could trigger slightly outside of it ((like how you tested and found it occurs closer to 0.6V). We build in margin to guarantee it occurs between +/-0.3V though it could happen outside of it.

    Same thing for trying to get out of the invalid state, if the input signal is outside of the +/-2.7V then we guarantee it will get out of the invalid state. But it could happen earlier (like at +/-1.5V), again we state higher numbers in our datasheet to guarantee across temperature, voltage ranges, and silicon variances that the device will behave as expected. Not all devices you test will get out of the invalid state at 1.5V and may move with temperature and if they come from different fabs. But they all should get out of the invalid state when outside of the +/-2.7V we state in the datasheet.

    -Bobby