[Transfer from RF Forum] How to cancel the indeterminate status of 26LS33?

[tony_lth]

I had designed a circuit to convert diff-line to single line with 26LS33, but sometimes there is a indeterminate status of the 26LS33. Can I use a pull-down resistor R15(100K) to cancel the indeterminate status?
See the schematics.

 

[FvM]

but sometimes there is a indeterminate status of the 26LS33

If the receiver is permanently enabled, as shown in your circuit, there should be no "indeterminate status". What do you exactly mean with this?

 

[tony_lth]

Hi, FvM,
Thanks.
Do you mean that circuit should have no indeterminate status? Only have High or Low output corresponding to the diff input?

 

[tony_lth]

How about if I remove the pull-down resistor?

 

[FvM]

Do you mean that circuit should have no indeterminate status? Only have High or Low output corresponding to the diff input?

Yes, due to the hysteresis. But I didn't test this specific line receiver yet.

A 100k pulldown won't have much effect in any case. It even doesn't clearly cancel the leakage current, if th edevice is tri-stated.

 

[dick_freebird]

The '32 has a couple hundred mV of hysteresis and an
open circuit failsafe. The output state is not indeterminate
per se, only if you do not know the history of the input.

Why would the inputs to the receiver be indeterminate?
And what is the nature of this indeterminism? Open? Short?
And then, what is to be the result? Work through this in
an orderly way (like FMEA) and maybe the solution will
show itself, or the problem decompose into "so what?".