I can see that the LT8361 has an example for 12V to -48V@290mA (page 25).
The LT8362 looks similar except for lower SW voltage but has a better package.
How do I determine if the LT8362 is suitable for my application?
If you need -48V from a 12V source the LT8362 is not your part. If your output voltage is lower, it might work.
For this type of inverter the switch sees the sum of the input and the output, so 12V…
For this type of inverter the switch sees the sum of the input and the output, so 12V plus 48V would be 60V, and you don’t want to operate a part at its limit.
Also, if you need more current than 290mA, it will help to know that
Thank you for the reply.
I need 12V to -33V@200mA.
I believe the LT8362 is modeled in LTPowerCad, which you can download from our website. However, the application you need appears in both LT8362 and LT8361 datasheets. The -24V CUK can be used for -33V app. You can use the one in LT8361, switching at 400KHz, or the one in LT8362, switching at 2MHz. Both have all the values you need. If the physical size of the inductor is too large for you, you can use a smaller one (same value). You might see a small additional power loss, but it will work. Just make sure the inductor you choose can handle at least 2A of current without saturating.
LTPowerCad does not support CUK for the LT8361/LT8362. The equations in the datasheet at least in my xlsx don't seem to match the -24V examples.
You are correct, I didn't think about that when I looked at LTPowerCad.
I don't know about your calculations, but both parts have a -24V CUK that would work for you, with only a change in the feedback resistor value. If all you need is a 12V to -33V converter, either one will work, even if your calculations say otherwise.
Thank you. It was the calculations in the datasheet that I followed. Anyway i looked at the inductor current from the LTspice simulation and they do not look as I would expect (triangle waveform) if you discount the HF noise. From what I can determine based on inductor rms current that the 6.8uF coupled inductor below would be suitable. Thoughts?
It is better to monitor the switch current, for clarity. The switch sees the addition of the current in the two windings, and should be about 1 amp, with the slopes added. If this current looks strange, then, be concerned.
When the inductor windings are on the same core (coupled), the currents look strange, and I'm not smart enough to explain the reasons.
Your inductor choice is a good one. You should have no problem.