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single supply negative input

Category: Hardware
Product Number: OP400S

Hello,

I'm trying to invert a -15V rail and step it down so I can connect it to an ADC input and get a voltage measurement.

My plan is to use an opamp to invert the -15V, and I was hoping to use the opamp in a single supply mode with 3.3V for +VS and GND for -VS. The problem I've noticed is that a lot of opamps will experience reverse breakdown of the ESD diode when the inputs are lower than the -VS rail. Also, ideally, I do not want to use the same -15V input I'm measuring as the V- rail on the opamp.

Would it be possible to use the op400 in this unipolar mode I described with a -15V input? Would there be sequencing issues or anything else I'd have to worry about?

If this isn't the right part for this, could you please suggest another space-grade part?

Thanks,

Anthony

  • Hello ,

    In general, the input and output of a precision operational amplifier is limited or bounded by the supply voltage/s. This means that you cannot input and output a voltage greater than +Vs and lower than -Vs using the op amp alone. 

    One option/recommendation that you can do is to increase +Vs to +15V or -Vs to -15V. By doing so, you can invert input signals up to +12V or -12V, but it still will not be able to invert signals up to +15V or -15V because of the output voltage head room and foot room of 3V as can be seen on the part's data sheet:



    Best regards,
    Paul