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LMV321: LMV321IDCKR not rail-to-rail?

Part Number: LMV321

Hi,

I'm using a LMV321IDCKR as unity amplifier and have the issue the op-amp seems to not work as rail-to-rail...The power supply is 3.1V. The positive input is connected to the power. The output is 2.4 - 2.56V and it fluctuates continuously.  I tried a few op-amps from the same batch and they all behave like this. i also tried a LMV321AIDBVR (different pinout) in the same schematic and the output is steady 3.1V...

What is this, a wrong batch or i'm not understanding how rail-to-rail works? Please advice!

All parts ware bought in the US from a reputable official dealer.

Thanks!

  • Hello Vilen,

    LMV321 is not a rail to rail input device. It is rail to rail output, although the VOL doesn't ever get to the rail. Once input is within about 0.7V of Vcc the input stage cuts off and the output can do multiple things, clamp to Vcc-0.7V, jump to Vcc , or do both.

    LMV321A is not rail to rail input either, but it does have dual input transistors as seen in schematic in data sheet section 7.2; this supports up to upper rail albeit at much reduced performance.

    The samples are performing normally.
  • Thanks a lot! It makes sense now.