Electrical – what does 3.4Vpp DAC output voltage mean

From what I've seen in datasheets, it looks like the ringing will usually be a few octaves above the bandwidth implied by the settling time (1/T). If that's what's really going on, a low-pass filter should help to dampen that ringing out. On the other hand, I rather suspect that the actual bandwidth and ringing are influenced more by the impedance of the load the DAC is connected to, and the settling time listed on the datasheet is going to be the optimal case caused only by the parasitic capacitance of the DAC itself.

The opamp output you are seeing is normal.

If we examine the circuit, starting with the opamp non-inverting input. We assume the input is infinite impedance so we first work out what voltage it's seeing:

We work out the bottom of the divider:

((R139 + R141) || R142)) = 1/(1/269.9 + 1/1000) = 212.54 ohms.

The top of the divider is R327 1k, so the voltage at the centre is:

3.3V * (212.54 / (1000 + 212.54)) = 0.578V

So the non-inverting input sees 578mV.

Now we look at the inverting side. We know that if the non-inverting input is 578mV, the inverting side must be at 578mV too. We also know that if the DAC outputs are off, then effectively the input is 0V, and the input resistance is R140 + R137.

So the input resistance is 269.9 ohms, and the feedback resistance (R326 || R136) is 1k || 1k = 500 ohms.
We assume the inverting input has infinite resistance, so we are left with a voltage divider.
With 0V at one side of the voltage divider, 578mV in the middle, the top side should be 0.578 * (269.9 / (500 + 269.9)) = 1.65V, which is what you are seeing.