I have modelled the LTC3872 as a boost converter in the configuration of Capture01.PNG.
It oscillates as in the Capture02.PNG.
Do you have any suggestion why and how to fix it?
As a test, I have replaced the MOSFET with a different part (Si7850DP, see Capture03.PNG) and now it works.
It provide 40V output [V(200)] and the FB voltage [Vref] is 1.2V after the transient (see Capture04.PNG).
Does this give us any clue?
Could you please make a zip-file containing both schematic files (.asc).
Then attach this zip-file to your next message.
Insert -> Insert Image/video file
Thanks for your request.
Zip file attached.
There is also a further option.
Results of the schematic with the DMN62D0U has been set up with a transient of 5ms.
The transient maybe longer (40ms or 80ms). In this case, LTSpice is taking long time to process results.
I did an attempt with 10ms and the processing nearly stopped before 5ms.
The LTC3872 has a build-in current limit. It turns-off the gate voltage whenever the drain-voltage reach 100mV to 270mV depending on IPRG. See the datasheet.
The first circuit with the DMN62D0U reach only a small drain current due to its high Rdson. The DMN62D0U is more suitable to drive small LED circuits, but not for an efficient DC/DC converter.
The simulation will not stall, when you add the SPICE-directive below.
.options gmin=1e-10 abstol=1e-10
The Si7850DP has a useful low Rdson for this application. That's why the circuit works as intended. Many other Power-Mosfets will fit as well.