I'm trying to build a +/-16.5V power supply using either two LT8364 (which I already have) or one LT8582 and a pair of LT3045-1 / LT3094 to post-regulate the output of the DC/DC converters. As I'm trying to make use of the VIOC feature, I'd like to run some simulations in LTspice.
However, I've run into an issue where the LT3094 is not behaving as expected when supplied with input voltages below -15V.
To reproduce, I've modified the LT3094 demo circuit very slightly to show the issue:
- I've removed the current limiting resistor (doesn't make a difference)
- I've changed the PGFB resistor divider for a threshold of -13.59V
- I've changed Rset to 140k for an output voltage of -14V
- I've changed the load resistor to 50 ohms
- I've changed the input voltage to -14.9V
This works as expected:
However, changing the input voltage to exactly -15V makes the circuit behave very strangely:
Further decreasing the input voltage, e.g. to -15.5V, will simply make the output of the LT3094 clamp to just above the input voltage, which is also unexpected:
Now the real funny thing is: if I replace the LT3094 with an LT3093, the circuit behaves as expected again:
This looks to me like a bug in the LT3094 model (I've a a handful of LT3094's on my bench and can confirm that they do indeed work with input voltages of -19V).
Unfortunately, there are a couple of differences between the LT3093 and LT3094, and I need around 400mA in my power supply. So while I can certainly do some simulations with the LT3093, I'd much prefer to use the LT3094 model.
I'm using LTspice XVII for OS X, build May 27 2020, 18:51:13.