I am trying to run SPICE simulation on the LTC3119. The objective is to evaluate solutions involving the MPPC functionality. My simulation appears to run correctly in buck mode (5V Vin, 3.3V Vout). However when I set Vin such that it would run in boost mode, eg Vin = 2.4V, it doesn't seem to make any sense. The Vin pin now outputs current driving current into the Vin source rather that drawing current from the Vin source. The Vout is still outputting current. How is this even possible? Also the simulation takes hours to run rather than only seconds in buck mode. I there a problem with the model in boost mode? All I change is Vin> Vout to Vin < Vout. I didn't spend a lot of time with it, but the "test fixture" simulation for the part seemed to have problems in boost mode also.