I have the following circuit built up in LTSpice which will be used to switch in different sense resistors for current measurements.
The mAEn signal switches the M1 transistor on at t=10ms which allow current to flow through the 30m Ohm resistor in branch 2. M3 in branch 1 is turned off the entire time.
Here is a plot of the voltage on Vdev.
The dip goes below 3.2V for about 10ns.
Now, if I remove Branch 1 like so.
I simulate this circuit, there is no voltage dip on the Vdev net as can be seen below.
Just cutting the line on the branch 1 path gives the same result (ie the following circuit also produces the same voltage as above with no dropout).
Why is it that turning on the transistor with less line impedance (branch 2) the voltage drops. This is like having a pipe with a small amount of water flowing, then opening a valve to another pipe with much higher water pressure and the pressure in the original water pipe dropping when you do it? Can somebody explain what is going on here?
What modifications can be made to the circuit to remove the transient voltage drop but have multiple branches?