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OPA2387: parameter problem

Anna
Intellectual 940 points
Part Number: OPA2387
Other Parts Discussed in Thread: OPA192

Hi Dear,

I have read the manual of OPA2387, and there is a maximum value of Differential in Chapter 6.1.as follows

May I ask how to understand this parameter and how customers consider it when designing circuits?

  • 0
    Guru 271250 points

    The single-ended input voltage is allowed to go 0.5 V beyond the supplies. But the difference between the two inputs is limited to the total supply voltage plus 0.2 V, so if one input is at (V+) + 0.5 V and the other at (V−) − 0.5 V, the resulting differential voltage of (V+) − (V−) + 1 V would be too large.

    In practice, you will be using signal voltages between V− and V+, and then these details do not matter.

  • 0
    TI__Mastermind 19177 points

    Anna,

    I agree with Clemens that the potential difference between the two inputs can be the entire supply voltage +0.2V.  Also, the single ended voltage each input can be as much as 0.5V above V+ or below V- to meet the ABS MAX ratings.  Some op amps have a diode structure between the inverting and non-inverting input to protect the input transistor pairs.  This diode limits the differential input to approximately +/-0.5V.  Devices with this diode structure can have some limitations when used with multiplexers (see OPA192 data sheet, section 8.3.1 for a discussion on this).  The OPA2387 doesn't have that diode structure so it gets the full supply voltage for differential range.

    Best regards, Art

  • 0 in reply to Art Kay
    Intellectual 940 points

    Hi Art,

    But as shown in the OPA192 manual, the maximum value of differential input is (V+) -(V-)+0.2，same as OPA2387

  • 0 in reply to Anna
    TI__Guru 62760 points

    Anna,

    There is no inherent conflict between OPA2387 and OPA192 having the same equation describing Absolute Maximum input differential voltage of (V+) -(V-)+0.2 BUT considering their absolute maximum supplies are vastly different, 6V (or +/-3V) vs +/-20V, respectively, in practice it mean 6.2V for OPA2387 and 40.2V for OPA192,

    Having said that, these are op amps and NOT comparators and thus both inputs should NOT be driven independently - in a typical operation a negative feedback drives the input terminals together within the virtual short (the same potential).