Other Parts Discussed in Thread: TLC555
Hello,
I'm having trouble with my LMC555 timer not performing the way I expect. My simulation in PSpice for TI gives the results I expect, but on the board I see something similar but with different timing.
My requirements are to have a hardware reset 5 seconds (ish) after being placed on the charger. To do this, I used two 555 timers: one intended to delay for ~3 seconds, and one to assert RESET_N for about 3 seconds (it must be asserted for 2 - 3.8 seconds). The circuit I came up with is:
When simulated for 10 seconds, the output is:
This is what I expect. In my project (KiCAD), I have the following schematic:
But when I look at the signals with an oscilloscope, I see this:
(Yellow = RESET_N, Green = VUSB, Purple = output of delay stage)
The issues I see here are:
- The delay stage should be ~3 seconds, but is really only about 1 second
- The RESET_N should be asserted for ~2.9 seconds, but is really only a bit over 1 second
For the simulation I am using the TLC555 timer, whereas the board has the LMC555 timer on it, but these message boards indicate that the parts are very similar.
Is there something silly I'm doing here?
Thank you,
Jonathan
