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Linux/TXS0102: TXS0102 VIL level and its actual functionality gives contradiction

Ronak Parmar
Intellectual 280 points
Part Number: TXS0102
Other Parts Discussed in Thread: SN74LVC2G17

Tool/software: Linux

Hi,

We are using TXS0102DQMR  IC for WIEGAND  interface which is support upto 100 meter of cable length. So low level will not maintain 0.15V with increasing the cable length.

We have done one exercise to verify the actual threshold level what we can get from this IC.

TXS0102DQMR
I/P (V) O/P (V)
0.48 0.5
0.6 0.65
0.65 0.71
0.84 0.88
0.9 0.93
0.96 0.99
1.16 1.2

Query:-

1. Please suggest that we can use this IC for our application what i have mentioned above?
2. In datasheet  VIL level mentioned 0.15V is really correct? 
3. If datasheet is right then why it is working at higher level of VIL ?
4. What percent we can rely for our specific application?
5. We can use this IC for longer length interface or you can suggest some other pin compatible replacement.
Please suggest!!
  • 0
    Guru 316690 points

    The TXS use passive MOSFET switches, which are on when the input voltage is below the transistor's threshold voltage. When a switch is on, it behaves like a small resistor.

    The VIL specification in the datasheet is not a 'real' VIL as for a digital input; its footnote says:

    The maximum VIL value is provided to ensure that a valid VOL is maintained. The VOL value is VIL plus the voltage drop across the pass-gate transistor.

    The TXS is constructed in this way to allow bidirectional translation with automatic direction sensing. If all you need is unidirectional downtranslation, then you could simply use buffers with overvoltage-tolerant inputs, e.g., SN74LVC2G17.