OP4177 Power Voltage Supply

Datasheet is not complete clear to me.

Does this opamp only work with a negative voltage at v- or can it also work with 0 VDC at v- and 5 VDC at v+?

  • Fons,

    We get this type of question a lot with respect to op amps, but it also applies to InAmps:

    --- 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.

     

    If you are doing a new design, I would use the ADA4077-4, which is the next generation OP4177.

     

    QUADS:  For precision signal chains, I would use two duals instead of one quad.  Better performance, easier layout, especially with active filters.  See:

     

    Planet Analog - Articles - Op amps: to dual or not to dual? (Part 1 of 2)

     

    Planet Analog - Articles - Op amps: to dual or not to dual? (Part 2 of 2)

     

    Harry

     

     

     

     

  • Harry, thanks for your input.

    Any idea why Analog use this way of specifying the power supply voltage?

  • Fons,

    Sure.  About 1970, with the 741 op amp, etc. analog signal paths were designed with +/-15V.

    PMI introduced the OP07 in 1974.  Since that time, we have done several more generations of the

    OP07 -> OP77 -> OP177 -> OP1177.  The OP2177 is the dual version, and the OP4177 is the quad.

    It is not too common to see systems that run on ground and +24V.  There are still quite a few

    systems that run on +/-15V and +/-12V.  Of course, with the scaling in CMOS technology,

    the world went to ground and 5V, then ground and 3.3V.  The CMOS processes have breakdown

    voltages approx 6V or less.  No one does analog with +/-2.5V, so the CMOS op amps

    usually have spec tables at ground and +5V or ground and 2.7V, or 3.0 or 3.3V.

    Harry


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