I have a voltage divider feeding into an op-amp voltage follower buffer circuit. I'm trying to calculate the voltage level at the non-inverting input of the op-amp vs. the source voltage. The possible supply voltage is roughly in the range
First I tried using a simple voltage divider, so:
$$ V_A = R_2 / (R_1 + R_2) * V_S $$
However, when I tried simulating this circuit in TINA-TI, the nodal voltages don't match those calculated.
I thought that was because the notion that there is no current flowing through the op-amp input wasn't truly non-zero, so I tried compensating for the op-amp input resistance and capacitance.
This time, the output voltage should be:
$$ V_A = (R_2 || R_3) / (R_1 + R_2||R_3) * V_S $$
While this equation does match TINA-TI's simulation of the no op-amp circuit, it still doesn't match the op-amp circuit.
What else am I missing?
further information: I'm using the LMH6612 op-amp.
Suppose I want to target an output voltage of
2.5V. According to my first equation the required source voltage is
~2.82V. By recursively updating my simulation I calculated that the actual required source voltage is
~3.47V. Using the second circuit the required source voltage is closer, but only marginally at