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Can I use the AD620 IA single ended up to 36 vdc?

I want to use the AD620 in a single ended application with a supply of 36vdc. Can I use it like that?

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  • Oh.  So your question really was "The AD620 is spec'ed for +/-15V, can I operate it on ground and +24V??"

    Here's a snippet from a recent email to another customer regarding op amps, but it also applies to InAmps:

    "We get this type of question a lot with respect to op amps:
      --- Your op amp is spec'ed on +/V, will it work single supply?? OR
      --- Your op amp is spec'ed on ground and +V, can I operate it on +/- supplies?
      With respect to dual supplies vs. single supplies, ALL op amps can run on both.

    The little electrons inside the op amp don't know where ground is, because there are no ground pins on modern op amps.
    So an op amp that is spec'ed for +/-15V operation, can run on +100V and
    +130V PROVIDED you observe the input voltage range (IVR) and output
    swings. The first op amps did not have RR inputs or RR outputs, so when National introduced the LM324 in 1975, it had a PNP input stage,
    so the IVR included the V- pin. So you could run it on ground and +V. So the official definition of single supply is:

    "An op amp whose input range includes the V- pin".

    To stay with this example, can I say to a customer, "Yes, you can use the part at dual supply +110V/+130V ? Does the part work in this case like specified at +-15V? Do we guarantee this?

    "All specification data in the +-15V table, exclusive of input/output range are valid; in other words, CMRR, PSRR, Isy, etc. are the same.
    Although note that the CMRR test conditions might be -10V <Vin < +10V, so you would have to adjust for this.

    When I was talking my network analysis course, the professor said you could pick any node for ground and write your equations for the other nodes in terms of that reference point.
    He also said to pick a direction for current through a resistor. If the number came out negative, it was going in the other direction.
    Again, there is no ground pin on the op amp, so if we measure a Vos of
    100 uV on an op amp with +/-15V supplies, and then move everything in the test circuit up by 115V, then you will have
    100V on the V- pin and 130V on the V+ pin. But the silicon doesn't know this, so the Vos is still 100uV.

    You could operate any op amp that is specified at +/-15V at 100V/130V with one BIG caveat: You have to keep the inputs and output within the rails.
    If you have an op amp that is specified at +/-15V and the IVR is -14V to +13V, then on 100/130V, the IVR would be 101V to 127V.

    In real life, this is not practical, because of power up/power down.
    Let's say you have a cap on the output of the op amp, and it is charged to +110V. When you shut off the power and the V- pin and the V+ pin go to zero,
    the cap will discharge back into the output stage and blow up the part."

    For InAmps, you need to worry about the Vcm, Vdiff, Vref, and gain.

    Most Inamp data sheets have "diamond" plots showing the allowable input range.

    But if your conditions are different, what do you do?

    We have a "diamond" plot tool that calculates everything for you.

    See:

    Instrumentation Amplifier Diamond Plot Tool | Analog Devices


    Depending on what you are doing and what temp range you need, I would look at newer parts:

    AD8421, AD8228, AD8222.

    If you are doing high side current sensing, I would look at the dedicated current sensing parts, such as 

    AD8417, or AD8418A.

    Harry

Reply
  • Oh.  So your question really was "The AD620 is spec'ed for +/-15V, can I operate it on ground and +24V??"

    Here's a snippet from a recent email to another customer regarding op amps, but it also applies to InAmps:

    "We get this type of question a lot with respect to op amps:
      --- Your op amp is spec'ed on +/V, will it work single supply?? OR
      --- Your op amp is spec'ed on ground and +V, can I operate it on +/- supplies?
      With respect to dual supplies vs. single supplies, ALL op amps can run on both.

    The little electrons inside the op amp don't know where ground is, because there are no ground pins on modern op amps.
    So an op amp that is spec'ed for +/-15V operation, can run on +100V and
    +130V PROVIDED you observe the input voltage range (IVR) and output
    swings. The first op amps did not have RR inputs or RR outputs, so when National introduced the LM324 in 1975, it had a PNP input stage,
    so the IVR included the V- pin. So you could run it on ground and +V. So the official definition of single supply is:

    "An op amp whose input range includes the V- pin".

    To stay with this example, can I say to a customer, "Yes, you can use the part at dual supply +110V/+130V ? Does the part work in this case like specified at +-15V? Do we guarantee this?

    "All specification data in the +-15V table, exclusive of input/output range are valid; in other words, CMRR, PSRR, Isy, etc. are the same.
    Although note that the CMRR test conditions might be -10V <Vin < +10V, so you would have to adjust for this.

    When I was talking my network analysis course, the professor said you could pick any node for ground and write your equations for the other nodes in terms of that reference point.
    He also said to pick a direction for current through a resistor. If the number came out negative, it was going in the other direction.
    Again, there is no ground pin on the op amp, so if we measure a Vos of
    100 uV on an op amp with +/-15V supplies, and then move everything in the test circuit up by 115V, then you will have
    100V on the V- pin and 130V on the V+ pin. But the silicon doesn't know this, so the Vos is still 100uV.

    You could operate any op amp that is specified at +/-15V at 100V/130V with one BIG caveat: You have to keep the inputs and output within the rails.
    If you have an op amp that is specified at +/-15V and the IVR is -14V to +13V, then on 100/130V, the IVR would be 101V to 127V.

    In real life, this is not practical, because of power up/power down.
    Let's say you have a cap on the output of the op amp, and it is charged to +110V. When you shut off the power and the V- pin and the V+ pin go to zero,
    the cap will discharge back into the output stage and blow up the part."

    For InAmps, you need to worry about the Vcm, Vdiff, Vref, and gain.

    Most Inamp data sheets have "diamond" plots showing the allowable input range.

    But if your conditions are different, what do you do?

    We have a "diamond" plot tool that calculates everything for you.

    See:

    Instrumentation Amplifier Diamond Plot Tool | Analog Devices


    Depending on what you are doing and what temp range you need, I would look at newer parts:

    AD8421, AD8228, AD8222.

    If you are doing high side current sensing, I would look at the dedicated current sensing parts, such as 

    AD8417, or AD8418A.

    Harry

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