Clarification Regarding Operating Principle of AD7745 IC - Single Ended Floating Sensor

[_pA89]

Can anybody (continue to) answer this thread posted @ADIEngineerZone

 

[_pA89]

Hi,

AN-1585 figure 2.

1. What is the Analog Devices Stand on AN-1585 ? (For Above - Take Any TI - Datasheet)

2. But be aware that an off-the-shelf capacitor has quite a large tolerance. ...calibration, acurracy disussions make no sense.

2. Even for Range Extension Circuit Resistors R1, R2 have Tolerances, Aging, ... AD8515 opamp has offset and other Errors.
--Without Analog Devices Specifying \( f_{error}(V_{ref},V_{exca}) \) does Scaling circuit makes sense ?
--One post - AD7745 HOW to decide Excitation Voltage Level - points to the approximately same question

3. Vref (=1.17 V)< Vexca/sig (=Vdd/2 = 1.65V) in AD7745, In ADCs Vsig < Vref ?

 

[stenzer]

Hi,

1. What is the Analog Devices Stand on AN-1585 ? (For Above - Take Any TI - Datasheet)

AN stands for Application Note. I don't know how the numbers are assigned. I do not know why TI is using a dedicated document name/number on their datasheet. Maybe this for traceability issues if the DS is changed/updated.

2. Even for Range Extension Circuit Resistors R1, R2 have Tolerances, Aging,

See reply #14.

--One post - AD7745 HOW to decide Excitation Voltage Level - points to the approximately same question

Please take at least the time to summerize findings, or copy the specific statement (including the link). I will not start reading several other discussions, until I find the ONE reply.

3. Vref (=1.17 V)< Vexca/sig (=Vdd/2 = 1.65V) in AD7745, In ADCs Vsig < Vref ?

What is your exact question?

Please state your exact application and your design goal. Your questioins are incoherent, short and are lacking of information. One has to make far too much assumptions.

BR

 

[_pA89]

Hi stenzer,

AN stands for Application Note. I don't know how the numbers are assigned. I do not know why TI is using a dedicated document name/number on their datasheet. Maybe this for traceability issues if the DS is changed/updated.

"TI-doesn't warranty its accuracy or completeness" - is what needs to be considered.

Please take at least the time to summerize findings,

Its so simple - "So, Would a result. Capacitance value (refere to digial code) ）change according to Excitation Voltage　setting?" (the thread has 2 valid posts)

What is your exact question?

If you want to help the question is obvious.

Please state your exact application and your design goal.

Posts #17, #19 and #3 (Summarize/Calculate Accuracy of Entire System Worst Case)

Your questioins are incoherent, short and are lacking of information.

You do understand the (*) datasheet is short, lacking of information.... One has to make far too much assumptions.

P.S.: Your pointing of MAS6510 -[7] https://www.mas-oy.com/wp-content/uploads/2017/02/DA6510_007.pdf did help a bit - (helpful ICs -MS3110, ZSSC3122, **broken link removed**). We can terminate the Discussion!

_pA89

 

[stenzer]

If you want to help the question is obvious

If you think so...

The reference voltage stated in the datasheet is the shown one in the sketch attached by you in reply #3. This is the reference voltage used by the implemented topology to determine the unknown capacitance, and is not the supply voltage of the following circuitry. So I still do not see a problem or even a question which indicates what are you concerned about, or where someone might help you. The equations given by you do not make sense as the voltages mentioned are not related, so for me it's not obvious how to give a correct answer.

As you prefere to give a short offhand statement instead of taking the time to elaborate your problems in more details, i will leave the discussion and this thread at this point.

Good luck with your project.