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AD585 internal op amp pin connection

Hi,

I am designing a sample hold circuit for ADC, and testing AD585.

The datasheet of the AD585 says the PIN1 and the PIN2 are -Vin +Vin (of internal Op amp) for DIP IC,

however the connection diagrams in Fig 6 Fig 7 Fig 8 inconsistent with typical integrator sample hold circuits.

In some traditional articles, the op amp input for sample-hold circuit should be as follows:

1) In non-inverting integrator sample hold circuit

Signal input should be connected to negative input of op amp and

feedback should be connected to positive input of op amp.

2) In inverting integrator sample hold circuit

Signal input should be connected to positive input of op amp and

feedback should be connected to negative input of op amp.

The actual circuit is working fine in Fig 6 diagram connection.

Is this some mistakes of the datasheet, in which the op amp's positive input and

negative input in the IC circuit diagram are reversed?

Thank you.

Ref:

IEEE JOURNAL OFSOLID-STATE CIRCUITS, VOL. SC-9,NO.6, DECEMBER 1974 381 A Complete Monolithic Sample/Hold Amplifier

Electronic Circuits: Handbook for Design and Application Ulrich Tietze、 Christoph Schenk、 Eberhard Gamm

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  • Hi:

    I didn't design the AD585 but I'm one of the few still reading this forum who have been around long enough to remember the insides of the circuit.

    The block diagram shown in the datasheet is a simplification of the actual transistor level circuit design. The two "op-amp" symbols in the block diagram are not actually full stand-alone op-amps that you might think of. Showing the connections as in the diagram is the simplest way to show gross functionality at the building block level. As you noticed the pin labels and connections are correct for the three gain settings shown in figure 6, 7 and 8.

    So if the circuit connections are working in your application then don't sweat the details in the (simplified) diagram.

    Doug

Reply
  • Hi:

    I didn't design the AD585 but I'm one of the few still reading this forum who have been around long enough to remember the insides of the circuit.

    The block diagram shown in the datasheet is a simplification of the actual transistor level circuit design. The two "op-amp" symbols in the block diagram are not actually full stand-alone op-amps that you might think of. Showing the connections as in the diagram is the simplest way to show gross functionality at the building block level. As you noticed the pin labels and connections are correct for the three gain settings shown in figure 6, 7 and 8.

    So if the circuit connections are working in your application then don't sweat the details in the (simplified) diagram.

    Doug

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