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Question about LMV358

Other Parts Discussed in Thread: LMV358, OPA374

Dear All,

I got a problem with a LMV358.

I'm using the DAC of my µc (STM32f205). This output is wired on a voltage follower (realized with a LMV358). The output of this voltage follower is wired on four minus inputs of LMV358 (use as comparator).

The problem that I have is that if I put 0 in my DAC registrer, I got 0V on the ouput of my voltage follower, if I put 500 in my DAC registrer I got about 500mV, if I put 4096, I haven't 3.3V but 2.7V. My DAC is working, because if I disconnect my LMV358, everything isd working fine (4096 = 3.3V). It looks like a saturation ?

So I've tried with another AOP (MCP602), now I got the entire excursion in input (0-> 3.3V) but in output, the maximum voltage that I have is 2.1V.

If somebody got an idea, because I don't know how solve my problem. I've tried to add loads..

Thank you.

  • Hello Fabrice,

    The LMV358 is NOT a rail-to-rail input device. It's input voltage range is limited to about 800mV below V+, or 2.5V. 2.7V is about where I would expect it to clamp. The LMV358 is working as expected!

    Look at the "Input Common Mode Voltage Range" line in the datasheet table - this is what is limiting you.

    The MCP602 specified input range is actually worse (1.2V below V+), but is a CMOS input device who tends to be more forgiving, but you are still violating their common mode specifications.

    You need a "rail to rail" INPUT device, that will cover the entire input voltage range. See the LMV931 or OPA374 or similar R-R input devices.


  • Dear Paul,

    Thank you for your explanation. I'll try one of this as soon as I'll be back to the office.

    Best regards,