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TINA - TI problem

Todd Price
Expert 3885 points

Other Parts Discussed in Thread: OPA314, LM358

“Attached are two circuits, one using an LM358 model provided inside TINA TI.  The other uses a model from your webpage for the OPA314.

8750.OPA314 test.TSC

2311.LM358 test.TSC

 The AC sweep for the LM358 matches what I expected for gain with about -4.5dB.

 The AC sweep for the OPA314 shows over -70dB of gain – not what I would expect.

 Can you check your OPA314 macro and see if it has a problem?”

Regards,

 

Richard (Garry) DuBose

Sr. Manager, R&D

iGo Inc.

17800 N. Perimeter Dr., Suite 200

Scottsdale, Az. 85255

480-477-3564

  • 0
    TI__Mastermind 40295 points

    Richard,

    The OPA314 circuit has been modified and uploaded to this page. Some DC offsets were added to the signal source and the ground connection of the feedback path.

    The 5V DC source (V2) on the signal source forces the OPA314 noninverting input  to a nominal mid-rail value of 2.5V (via the R5/R6 voltage divider).

    The 2.5V DC source added to one side of R4 forces the OPA314 inverting terminal and output terminal to the 2.5V mid-rail.

    Forcing the nominal DC voltage on the OPA314 pins to mid-rail will maximize the circuit's available voltage swing.

    Using a single-ended supply without these extra offsets will frequently cause at least one of the device pins to operate near the power supply, or ground.
    This leaves the circuit with no available voltage range to support signal swing.
    Many op amps can't cope with this kind of operating condition.

    However, some devices are designed to work under these conditions, and these are usually designated as rail-to-rail on the input (RRI) or output (RRO) or both (RRIO). Some devices also have internal offsets built in so they can work with signals that go below ground in a system with a single supply.

    If you have a  TI apps engineer or techical sales rep supporting you, they should be able to help you pick the best device for your application.

    Please let me know if you have any more questions.

    Regards,

    John

    8750.OPA314 test_Modified.TSC
  • 0 in reply to John Miller - Sensing
    Prodigy 20 points

    OK, thanks for the information.  In the last few days I have added a BIAS input on the + opamp input that puts the output at about Vdd/2.  Also have AC coupled the signal input to work into that pin.  Circuit performs as expected.

    Its been a long time since I worked with Spice in general, so I make foundational mistakes.

    Garry