I have a PCB with voltage regulator (5V), op-amps, 2 multiplexers, 1 counter, several pots, caps, and resistors.
I supply 9V. The voltage regulator converts it to 5V. Without connecting any TTL signal through the function generator, I probe the input and output pins of the counter and I see a jump from 0V to about 2V in ~4ms. Then when I turn the power supply off, I see another jump from 0V to about 1.44V in the 10ms range.
I notice this behavior when I turn on and off the power supply. I removed the counter and op-amps, and I still see the spike in voltage but in the ps range and only when I turn the power supply off.
There is an overshoot from the power supply where it jumps to about 10V then back to 9V. There is also a tiny transient voltage but it is very small and I have the necessary passive components at the voltage regulator to control this.
I do not know what is causing this issue. Tried different things, I breadboarded the voltage regulator by itself and I do not see any issues at the 5V output, I added just the counter, and I saw this issue, it seems like whenever an active component or IC is added this issue occurs. Can this be a PCB manufacturing issue? Any suggestions?
I see, I was not clear enough.Lets forget what I said in the block above. I made something to make this clear, see below. I also wrote my questions there.
I kept the recommended design set up for the regulator and I'm only powering the counter as seen below. I'm not providing any input signal or anything else. All of this is done on a breadboard. I have a more complex circuit on a PCB but I still see similar issues. That jump at the output pins is an issue for me.
Data input is grounded on the counter.