# ltspice, plot Vpp

Maybe this is extremely trivial.

I have a transient analysis over a buck regulator and can't figure out how to plot Vpp. I just want to sweep some capacitors and see the ripple.

In PSpice you can add expression directly to plot (like V*sqrt(2)), I can't figure out how to do this in LtSpice. If I click the name of the plot, I can enter some expression but always gave me error such as "undefined symbol" Vpp(noo4)

I also added a .measure directive in schematic but nothing happens to the plot

.meas TRAN x PP v(n004)


What I miss? Thank you.

My buck's output

• Look in the log! That's where the result appears. – winny Feb 15 '17 at 10:33

vpp measurement in ltspice is a single value over the whole plot (or a section thereof, check .meas parameters). Look in the error log (weird place, I know)
For sweeping multiple values of a single component, use the .step param facility, and then you can right click in the error log and plot the .meas values vs. component values.