Electronic – How to correctly simulate a simple LM2907 circuit in LTSpice

You can simulate any part for which you can get or build a model.

Making a model would involve creating a combination of resistors, capacitors, controlled sources, etc., that represent the behavior of the part as a subcircuit in your simulation. For some parts, like maybe a simple op-amp, it's reasonable to try to construct a model like this from information on a datasheet. Although of course you'll only capture the behavior that's represented on the datasheet --- you won't necessarily have correct behavior in corner conditions, in cases when the power supply is not one of the spec'ed levels in the datasheet, etc.

An easier way to get a model is if the part's vendor provides it. However in this case it doesn't appear that Diodes Inc provides a SPICE model for this part. The available SPICE models from Diodes Inc are listed here.

In fact, it's not common (except from Linear Tech) for switching regulators to have SPICE models available. The main reason is that traditional SPICE doesn't model digital switching circuits very efficiently -- LTSpice has significant improvements compared to previous SPICEs in this regard. But other vendors are unsurprisingly not enthusiastic about providing models tied to their competitor's simulation tool. Also, the availability of models for LTSpice is one of the main selling points of LT's switching regulators, so LT is understandably unenthusiastic about enabling other vendors to create LTSpice models for their parts.

So in this case, I think you'd have a lot of trouble creating a model of your circuit. It may cost you a dollar or two extra to use a comparable regulator from LT, but if simulation is important to you it's probably worth it. It's certainly cheaper than doing a re-spin of your board if the other part doesn't work, assuming you're not talking about a project where you'll eventually build 1000's of parts.

Yes, you can inject noise using the arbitrary voltage (or current) source, then use things like the random or white function to create some noise.

Here is an example circuit (I separated the noise from the signal just to make things clearer - obviously you can combine them together in one function if you wish):

Simulation:

All the functions are detailed in the help under circuit elements -> arbitrary behavioral voltage or current sources.

Noise simulation mode

Also, just in case you were not aware, SPICE has a noise simulation mode, to quote from the help files:

.NOISE -- Perform a Noise Analysis
This is a frequency domain analysis that computes the noise due to
Johnson, shot and flicker noise. The output data is noise spectral 
density per unit square root bandwidth.

Syntax: .noise V(<out>[,<ref>]) <src> <oct, dec, lin> <Nsteps> <StartFreq> <EndFreq>

Basic example:

Simulation:

The above is rather boring as it only models the resistor noise (I stepped the resistor through various values to show how the Johnson noise increases with resistance). But it can be very useful with more complex circuits containing diodes/transistors/opamps/etc.