I’m trying to do a simple transient analysis involving some TI power management components, one of them being a LM27761 which has output voltage controlled by gain-setting external resistors. It looks like the output voltage isn’t budging (stays at 0V forever) even though the schematic seems correct. The expected output is -2.5V. For reference, I have simulated the same circuit on a previous version of QSPICE (I don’t know which), and it was fine back then. I had to re-import the SPICE model and re-draw the schematic on the current version and now it has stopped working. The circuit works fine on a PCB. Am I missing something here? I would attach the schematic but I am not allowed to. Thank you in advance!
Current schematic on the left, previously obtained result on another version on the right:
Model downloaded from:
Just tried it, it still stays at 0V. It also takes an extremely long time to run the simulation for some reason. I wonder if there is something about the PSPICE model that makes it incompatible with QSPICE?
do you get any warnings in the Output Window?
I do get a warning
Ignoring shorted resistor: "R_R9●X3" referring to the device in question, but I don’t think it is relevant.
Fast (less accurate) Math in Edit > Preferences, does it help?
This is a circuit which can work in my test. It always a challenge to make a TI Pspice transient model to work in Qspice in my experience. Most of the time it is better to add UIC in .tran to skip .op. TI Pspice model normally have lookup table, formula and unrealistic devices and hard to know which part giving us challenge to make it work.
I change retol=1 to speed up this simulation. But If I add a load to V(OUT), simulation won’t work with retol=1 but have to disable it to its default retol=0.1, but simulation run very slow in such a situation.
Parent.LM27761.qsch (18.0 KB)
Wow, thank you, I have learned a lot from this example. I will take note of this when importing TI models!