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TL331: TL331

Part Number: TL331
Other Parts Discussed in Thread: LM339, LM393

Hi,

   I am using TL331 for one of my application as simple comparator. (Without hysteris).

I have set the Ref as 2.5V to inverting pin and given sign wave of Amplitude 4V and Freq 400Hz to non inverting pin. I am seeing a glitch in the output waveform. Can you help me to sore this Issue.

Attaching the sch and waveform for your review.

  Regards

Anuraj NK

   

  • Hi Anuraj,

    this is phase reversal because your input signal exceeds the common mode input voltage range. See section 9.2.2.1 of datasheet.

    Kai
  • Hi Kai

     I understood that, the maximum common mode voltage of 3.5V since my supply is 5V.  I have given input as below

    Supply : 5V

    Vin + : 4 Volt

    Vin- : 2.5 Volt

    Looks like, I wont be able to configure my comparator for above requirement with TL331. Can you suggest /share the application design document.

    Waveform have glitch only after second pulse and it is repeating the same fashion. whys it is so?  How can I fix this issue.

    Please find the waveform attached.

  • Hello Anuraj,

    You are now exceeding the negative input voltage. I assume you are using a single supply (+5V and GND).

    The "legal" input range is -0.2V to +3.5V on a single 5V supply. It looks like your input is going negative.

    The plots don't have enough resolution, but it looks like the input voltage is going below ground on the negative peaks, possibly causing the input to clamp negative. The LM339/LM393/TL331 family is very sensitive to negative input voltage and the output may "invert" when the input is pulled below ground. This is most likely causing the "spikes".

    So you are exceeding the 3.5V limit (as Kai pointed out) and also the -0.2V limit. Try attenuating the input voltages (resistor divider) to bring the comparator input voltages to within the limits.

  • Hi Paul,

      Please find my understandings inline with your answers

    You are now exceeding the negative input voltage. I assume you are using a single supply (+5V and GND).

    Replay : I am using a single supply (+5V and GND).

    The "legal" input range is -0.2V to +3.5V on a single 5V supply. It looks like your input is going negative.

    Replay: Input at Vin+ is non negative and Vin- is Vref =2.5V.

    When you say input voltage is negative, you are considering (Vin+) - (Vin-) right ? or (input voltages at (Vin+) and (Vin-).

    In general for a comparator, (Vin+) - (Vin-) can be positive or negative. Kindly correct me if I am wrong.

    The plots don't have enough resolution, but it looks like the input voltage is going below ground on the negative peaks, possibly causing the input to clamp negative. The LM339/LM393/TL331 family is very sensitive to negative input voltage and the output may "invert" when the input is pulled below ground. This is most likely causing the "spikes".

    Replay: Refer the attached document for the application circuit and the zoomed waveform captured. Vin+ and Vin- is always positive value.

    Regards

    Anuraj NKComparator Observations.pdf

  • Hi Anuraj,

    that's the first plot you gave us. It shows the input voltage and it's definitely going negative:

    Kai

  • Anuraj
    There has not been a new entry in a while so I am closing this post out. Feel free to re-open the post by hitting reply if you need further assistance.
    Chuck