TINA/Spice/OPA2626: Noninverting circuit output reference voltage drop with Tina

Hayden Shin

Part Number: OPA2626
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

I made noninverting OP-amp circuit with OPA2626(626) and tested with Tina

Ref voltage is 1.65V, and input signal is swing 2mV PP from 1.65V. And gain is 100

However, when I changed reference register value(Same Gain), output common mode(Reference) voltage is dropped(Signal is amplified properly)

And when I changed OP-Amp to basic OP-amp in Tina, output voltage reference voltage drop is not happen

Please refer to below Tina schematic and waveform and let me know my missing point

over 7 years ago

0 John Miller - Sensing over 7 years ago

TI__Mastermind 33240 points

Hayden,

Would you please upload your TINA schematic to this thread?

Regards,
John

0 Hayden Shin over 7 years ago in reply to John Miller - Sensing

TI__Prodigy 460 points

Hi John,

Please refer to attachment

Thank youHayden OPA626.TSC

0 John Miller - Sensing over 7 years ago in reply to Hayden Shin

TI__Mastermind 33240 points

Hayden

Thanks for providing the schematic.
Your schematic was rev'd by adding some voltage and current probes and running a DC operating point sim.
It is shown in the graphic below.

The graphic shows the model's input bias current at the inverting pin is approximately 2uA, which agrees with the spec in the device data sheet.
Most of the 2uA bias current flows through the 100k feedback resistor.
This results in a 0.2V drop with respect to the voltage at the inverting pin (= 1.65V).
So the resulting output voltage is VOUT = VREF - IIB*RF = 1.65 - 2uA*100k = 1.45V.

When a 1k feedback resistor is used, the drop is 2mV, which is too small to show up easily on the TINA displays.

I hope this helps.
Please let me know if you have any questions.

Regards,
John

0 John Miller - Sensing over 7 years ago in reply to John Miller - Sensing

TI__Mastermind 33240 points

Forgot to attach the graphic in my last replay.
Apologies for that
John

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TINA/Spice/OPA2626: Noninverting circuit output reference voltage drop with Tina