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Question asked by HOD on Aug 9, 2018
Latest reply on Aug 10, 2018 by GlenBrisebois



I have a question LT1711.


· About 10 VTH and VS in the data sheet
Is VS the potential difference between + IN and - IN of the LT1711?
(If VS is 3 V, + IN is + 1.5 V and - IN is -1.5 V?)

Is VTH the voltage actually applied to the input terminal of the LT1711?
For example, if VS is 3 V and data sheet constant is implemented
Since it is stated that the attenuation amount will be 0.0978, for the input signal 3 V
Values recognized by the comparator as input signals are 3 V x 0.0978 = 0.2934 V
Is it that?

· About the content you responded about hysteresis
About 240 / 750k =. 03% in original text. With 3 V drive
Is 240 a value twice that of R 3? Or Z 0 = 120 Ω in the data sheet
Is it twice the value of Z0?
In addition, 3 V drive is not the above VS but the input supply voltage of the comparator
(3 V in the data sheet figure) is it?


Answers I gave before:


The hysteresis is very small, because the large 750k feedback resistor looks back into the relatively low impedance of R3 looking back into the 120 Ohm line. 

That impedance is about 240 Ohms, so the hysteresis as a percentage is 240/750k = .03%.  With 3V drive, that is 1mV.  But it is applied twice, so total hysteresis is 2mV. 

Hysteresis could be increased by reducing the 750k resistors.  Note that the full scale signal at the receiver inputs is only 700mV differential, because of the attenuation of the resistor networks.


The threshold is 0V, differential, over a fairly large valid CM range.  (But of course hysteresis sets each real trip point a little bit away from that.)



Best Regards