I have a relaxation oscillator circuit, which is supposed to oscillate around 6 MHz, and mostly it oscillates in a very stable manner around it.
However sometimes it starts to oscillate at 25 MHz, which is the fastest oscillation available for this comparator (TLV3202) given its propagation delay is 40 ns. Some cases where this happens are:
- on frequent on-off, I can put the circuit in this mode
- bringing fingertip near inverting input, not touching just in air.
- touching an open ended wire to non-inverting input.
- also during normal handling of running circuit we have seen this. As this circuit will be used for further capacitive sensing, we are in trouble.
A few observations:
- touching non-inverting input with an open ended probe bring it back to 6 MHz
- or power reboot also fixes it.
A few things that I tried to fix this, with no success:
- putting a 10 pf capacitor between comparator-output <----> comparator-non-inverting input.
- putting a 200 ohm resistor on comparator-output.