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LMV331: Hysteresis circuit error

Yongki Jeong1
Intellectual 545 points
Part Number: LMV331
Other Parts Discussed in Thread: TLV9020

Tool/software:

Hi Ti team

I designed a Hysteresis circuit using LMV331 to power off at high temperature and turn it back on when the temperature drops.

However, the Output swings before and after the switching section.

Also, the V+ voltage does not change immediately even when the Output changes.

I don't think the IC will behave abnormally at a temperature of around 55 degrees.
I would like to ask for help if there is an error in the circuit.

- VL : 0.7V

- VH : 0.95V

Cycle TEST)

- Red : Thermistor

- Green : V+ of LMV331

- Blue : Green - Red

- Purple: Output of LMV331

close up)

  • 0
    TI__Genius 11025 points

    Hi Yongki,

    Are the resistor values exactly as you've shown on your schematic? I hand-calculated and simulated the circuit with the 4-digit EIA values shown in the schematic, and I'm not getting the same VH and VL as you've indicated in your post:

    What's the time per division of these plots? Is there any way you could show images directly from the oscilloscope?

    It is strange that it seems like the output seems to switch output high even when there's a large negative differential at the inputs. Could you depopulate R9525 (0 ohm series resistor to NMOS) and seeing the results of the test?

    In addition, how does VDC_3V3 look like at the LMV331 VCC pin? Is it a clean 3.3V? It may be beneficial to increase the value of the bypass capacitor to ensure a clean VCC.

  • 0 in reply to HO SIU
    Intellectual 545 points

    Hi Ho

    Sorry, R89 is 91K, not 910K.

    I set the cycle so that the temperature can change every 5 minutes.

    I used Multi Channel Monitor to see the voltage change while doing high temperature test. Time is 1 second interval.

    When I connected the variable resistor and measured the voltage with an oscilloscope, it was normal.

    I haven't measured it in a temperature chamber yet.

    So I wonder if there have been cases where this symptom occurred at high temperatures.

    Regards.

    Jeong.

  • 0 in reply to Yongki Jeong1
    TI__Guru 60306 points

    Hi Jeong,

    Keep in mind that the LMV331 is not a Rail-to-rail input, and the valid input voltage range is Vcc-1V, or 2.3V max on a 3.3V supply. Make sure your input voltages are <2.3V or the output can misbehave.

    Try a TLV9020 that is a R-R input and can drop-in replace the LMV331.

  • 0 in reply to Paul Grohe
    Intellectual 545 points

    Hi Paul

    How about TLV7031SDCKR which is cheaper?

    It should be South East Type with SC70 package

    Regards.

    Jeong

  • 0 in reply to Yongki Jeong1
    TI__Guru 60306 points

    Hello Jeong,

    Yes, that one, too. I forgot about the TLV70xx family "S" pinout option. Since the '31 is push-pull output, you do not need the pull-up resistor (R10077).