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Part Number: OPA189
Tool/software: TINA-TI or Spice Models
Hi Guys!First of all i would like to share my conpect with you.I use ADS1262 for a long time, it is perfect for us , but now i need to measure voltage more than "+/- 2,5V".A found schematic what is looks like what i want to do, i attached the file.
I except from this schematic that the V+ is always VCC/2 and V- is swing within 0-5V more or less.But if i made the simulation i did not get the same results.
I Would like to measure +/-24V , couse what if someone switch the plugs(5V) in this case it should be for example not +5V, -5V.
Maybe i missed something or ?I hope some of you guys can help me.The biggest problem with our design is the limited space , i dont have space for negative supply for the OPA and ADS1262.RegardsBalazs.
ps.: this picture came from the TIDA-00879.OPA189FORADS1262.TSC
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In reply to Thomas Kuehl:
Thomas KuehlIt is not clear which source is being swept in your TINA circuit
The VG1 is running from -24 to +24V. I exacpt that the U2 is sweeping from ~+5V to ~0V. but is running from ~2,5 to ~0V.
Thomas KuehlWhere is the +/-24 V being connected? Is the +/- 24 V referenced to the same ground as U1, U2?
Thomas KuehlIf not, what is the intended common-mode voltage?
The common-mode voltage is AVCC/2, U1 made this.
To the first picture is want to copy this section from the TI Guidline: "The AFE subsystem measures voltage by applying the external device-under-test (DUT) voltage between the voltage+ (red) and voltage– (black) terminals. These inputs terminals support both positive and negative voltage polarities". Well i want to simulate this postive and negative voltage polarities.I hope you can see where i stucked.
In reply to balazs buglyo:
Hi Balazs, you have taken the wrong OPAmp for the simulation: The OPA189 is no input rail to rail OPAmp. If you increase the supply voltage for the both OPA189 to 10V the simulation will work. Kai
P.S. Sorry, edited "no output rail to rail" into "no input rail to rail".
In reply to kai klaas69:
Alternately, you could use precision op amps that are specified as having rail-to-rail input and output ranges. The OPA196 is an example of such an amplifier. Then, the +5 V supply could be used as you originally planned. You can find my TINA simulation file and an image of the results below. I redrew the circuit and used a 1 Hz triangle wave for the +/-24 V input.
Precision Amplifiers Applications Engineering
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