• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 48 subscribers
  • Views 396 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLV1812: Regarding the problem of oscillation at the input of TLV1812

Kazuki Takeda
Prodigy 10 points
Part Number: TLV1812


Tool/software:

Hello,

I use TLV1812 as a window comparator.

Pin 2 of TL1812 in the schematic below is oscillating.

Oscillation occurs when the input voltage falls below the reference voltage of -22mV.

When the input voltage is below the reference voltage of +22mV, it does not oscillate.

Can you think of anything that might have caused it?

  • 0
    Guru 318050 points

    Your circuit does not have hysteresis. Add positive feedback (e.g., 1 MΩ from the output to the non-inverting input).

  • 0
    TI__Intellectual 1320 points

    Hi Kazuki,

    Does this oscillation stop if you go a certain point past your -22mV ref? 

    As Clemens mentioned, you don't have hysteresis which would be helpful to prevent this chatter. This part also has 4 mVOS which is close to your 22mV reference so hysteresis would again be helpful here.

    I see you have the resistors spec'ed with a temp coefficient, do you know the resistor tolerance for these? this may move your reference around.

    Best,

    Michael 

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Thank you for your reply.

    Oscillation occurs only at the -22mV reference voltage, should I put positive feedback on the one where oscillation is not occurring?

    I don't want to change the reference voltage too much in the design, but if I add hysteresis, the input voltage at which the output switches between high and low will change.

  • 0 in reply to Michael Hawkins
    Prodigy 10 points

    Hi Michael,

    Oscillation occurs when the input voltage falls below -22mV and stops when it rises above +22mV.

    Oscillation is also stopped by an input voltage below -26mV.

    Resistance tolerance is ±0.5%.

  • 0 in reply to Kazuki Takeda
    TI__Intellectual 1320 points

    Ok, it's odd that it doesn't also occur on the +22mV ref channel. If you can, try to adjust the input voltage precisely to see if you can get chatter on that channel's output. 

    This oscillation seems to be chatter coming from some combination of noise, resistor tolerances, and input offset voltage of the comparator.

    For R3 you can make it larger to tighten the hysteresis window, attached is the TINA file.

    TLV1811.TSC

    Let me know how this works.

    Best,

    Michael