I'm looking at using this device as a low power VCO at 240 kHz. I would like to model it along with some of the associated circuitry, but the company doesn't provide a spice model. I was wondering if anyone knows how this thing works internally enough that a model could be created.
Don't know about LT. I think this part may be a second source for a part by Maxim or someone similar. I haven't found that part yet.
I am working on my own model, but LTspice isn't always easy to use. Like many tools it is not easy to pick up again after you don't use it for a year or two. I can't seem to get a hierarchical model to work properly.
I'm just constructing a functional model which will charge and discharge a cap from a pair of constant current sources as controlled by a FF triggered from the voltage trip points. That sounds like what they are doing based on the description in the data sheet. I'm not a proper analog designer so I don't know how their current source works. It seems to pass a current determined by the set resistor. I expect they are using current mirrors to scale a current in the resistor to the current to the cap. I don't think I need to simulate all the details. I just want to get a warm fuzzy that the control loop will work ok. The part I really have no idea about is how the resistors for the VCO input interact with the current source. This may be important. We'll see...
I was kinda hoping some of the chip gurus here would offer some opinions of how they thought this circuit might work. The company FAE has been very helpful in running some tests for me to make the chip run at my frequency and show that the VCO control will work. He hasn't been able to answer any of my detailed questions on how to get a fine control rather than a coarse adjustment. I also don't get any sense from him of how the chip works on the RSET pin. He just doesn't answer those questions and I don't want to bug him further. Its not like I'm going to be buying a million of these things.
In reality I'd prefer to make my own VCXO, but I can't find a 240 kHz crystal. Whatever, I think I can get this to work even if I have to play with it on the workbench. I prefer to simulate and get it right the first time as my eyes make it hard to solder the small stuff these days.