The DC drop calculation needs a voltage source to start with. In this case, the voltage source is part of the VRM model. You need to assign a VRM model to at least one pin on the power net that you want to analyze. That pin might be the output of a linear voltage regulator, the output pin of the inductor of a DC-DC converter, or a connector pin where an external power source connects to your design.
For correct DC drop results, you need to specify the correct output resistance of your VRM, but not the inductance value. The inductance value is used for decoupling and impedance analysis.
the error was
DC Engine failed: No connected VRMs found in reference net
its about the reference and not the VRM itself
the thing is that i defined the reference net but it is connected to the VRM throw common mode choke witch i defined also to be a very small resistance
but the simulation keep fall on that
It's hard to know the solution without seeing the design, but here are a couple of things to look at.
- is the net connected to the reference (or ground) in of the VRM defined as a power net?
- is the common mode choke recognized as a series component? If it has more than 2 pins then you need to get creative.
One thing that you can do is to take the reference net out of the simulation. In the DC Drop setup dialog, uncheck this box for reference net.
The DC drop analysis will run through just the power net. You can run the DC drop separately on the reference net, and add the results to get the final voltage at the power sink.
Another thing to look at is to find the intermediate net between the choke and the power sink device. That net is probably not defined as a reference net. If you define it as a power net with 0V, then it should be available to assign as the reference net for the power sink device.