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TLV7041: Inverting comparator circuit not working as expected

Richard Thompson
Prodigy 220 points
Part Number: TLV7041
Other Parts Discussed in Thread: TLV7031, TLV9032, TLV9022

I have built an inverting comparator circuit in TI Tina.  I copied the circuit from the TLV7041 data sheet (SLVSE13G – SEPTEMBER 2017 – REVISED DECEMBER 2020- page 20-21).  The circuit is for a TLV7031!  I believed that it would work using the TLV7041, but I needed a pull-up resistor on the output.

The circuit is designed to compare the reference voltage of 5V to the input (neg).  The High to Low trip voltage is 3.33V and the Low to High trip voltage is 1.67V

The circuit output does not change state at the trip voltages, using the pull-up resistor.  Removing the pull-up, the output is around 2V, not the 5V reference voltage that I expected.

I have attached the circuit.

Sandbox.TSC

  • +1
    TI__Guru 53946 points

    Hi Richard,

    Yes. You can use a open-drain output device with hysteresis. You just need to calculate the pull-up resistor in series with R3 (the feedback resistor).

     See the following appnotes:

    Inverting comparator with hysteresis circuit (Rev. A)

    Non-inverting comparator with hysteresis circuit (Rev. A)

    Two problems..

    First issue.... You cannot "float" the input when the switch is OFF. The switch has a default parallel ON and OFF resistance and is not "infinite".

    When ON, the default resistance is zero ohms.

    When OFF, the default is 1Gohm (max is up to 1/GMIN).

    The ON/OFF resistance values can be set in the Properties of the switch (left click on switch - Properties).

    So when you turn it OFF, against the high impedance input, there is little voltage drop across the resistance due to the low bias current, so the input pin is still around 5V.

    Put a voltage monitor on the input pin and you will see it is still be around 5V when "OFF".  So either put a pull-down resistor from the input to GND, or get rid of the switch and set the voltage source to 0V or 5V.

    The second issue is not your fault. There seems to be an issue with the model. I'll look into it.

    In the meantime, you can use the TLV9022 model (or TLV9032 if you want push-pull out):

     TINA Model for TLV9022

     TINA Model for TLV9032

  • 0
    TI__Guru 53946 points

    Hi Richard,

    Not sure what happened, but when I replaced the TLV7041 with a "fresh" TLV7041 in your circuit, it started working (along with the suggested input pull-down resistor).

    See attached:

    Sandbox-Fixed.TSC