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TL081H: TL081H output is not going to 0, when input is 0V.

Anjali Khiratkar
Prodigy 40 points

Part Number: TL081H
Other Parts Discussed in Thread: TLV9301

I am using TL081H,

VCC= 12V,

In = 0/3.3V, (0 when it is off)

I have seen Vout as 0.6V, 0.7V, 1.6V in multiple boards, even though the input was 0.

1) In datasheet, Vcm mentioned is (V- + 1.5V), will it swing above 1.5V even if Input is not there?

2) Will it get resolved, if i use TLV9301?

Thanks.

image.png

  • 0
    Guru 321820 points

    1. When the input voltage is outside the Vcm range, then the device is no longer guaranteed to work correctly. The output voltage could by anything.

    2. The TLV9301's Vcm includes 0 V, so it will work. (But the TLV9301 works only with input voltages up to 10 V.)

  • 0 in reply to Clemens Ladisch
    TI__Expert 4330 points

    Hi Anjali,

    The output voltage range of the TL081H doesn't go to the negative rail, so with a single supply of +12V (V+ = 12V and V- = 0V) and an input voltage of 0V, the output of the amplifier won't be exactly 0V and the limit varies between parts. 

    The spec "Voltage output swing from rail" shows how close the output voltage can get to the positive and negative supply rails. The maximum negative rail headroom (with a 40V supply and 2kOhm load) is 1030mV. 

    However, for the TLV9301, which does have a rail-to-rail output, the output voltage can get much closer to the negative rail:

    For more details on input and output limitations, see our white paper on Op Amp Input and Output Swing Limitations, as well as Understanding Operational Amplifier Specifications.

    Let me know if you have any questions.

    Best Regards,

    Alex Curtis

  • +1
    Prodigy 40 points

     Hi Alex,

    Thanks for the explanation.


    With a single supply (12 V / 0 V) and 0 V input, can the TL081H output ever exceed ~1.5 V under any condition (temperature or load)?


    I m planning to use a pull-down resistor and route this signal to another peripheral when the TL081H is in the off condition, so I want to confirm the maximum possible output level.

  • 0 in reply to Anjali Khiratkar
    TI__Expert 4330 points

    Hi Anjali,

    With 0V on the input, the opamp output will be as close to 0V as it can get, limited by the output voltage swing from the table in my last post. The output voltage for the TL081H in this condition would be at most 1030mV at 25C with a 2kOhm load, but this voltage would increase depending on the output current and temperature. 

    In short, it depends on the load connected to the output of the amplifier. See Figure 5-14:

    Based on the plot, if the amplifier is sinking a small amount of current (less than 10mA at 125C) then the output voltage shouldn't exceed 1.5V above the negative rail, but sinking ~15mA or higher at 125C would cause the output to go above 1.5V.

    Best Regards,

    Alex Curtis