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OPA2170: Can OPA2170 short-circuit output current limits be adjusted to custom levels during test process at TI?

Part Number: OPA2170

Can OPA2170 short-circuit output current limits be adjusted to custom levels during test process at TI?

  • In reply to Ron Michallick:

    Ron,
    This looks very reasonable. I look forward to hearing about your results. I think it'll work.

    I found the stabilizing network in this blog post:
    e2e.ti.com/.../do-it-yourself-three-ways-to-stabilize-op-amp-capacitive-loads

    I did step response and saw minimal overshoot as described in blog post. I think this means it's stable, but I'm not sure. How would I need to modify this TINA schematic to simulate for stability?

    Regards,
    Dave
  • In reply to Dave Knight:

    Dave,

    There are a few ways to check stability.

    For multiple feedback paths to inverting pin only, I break at inverting input and add C5 (expected input capacitance to ground )

    Phase margin is 74 degrees at 210 kHz and gain margin is 43dB at 8.2 MHz

    opa2170 bode (gainphase).TSC

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Dave,

    Here is IOUT vs VOUT.  No pnp is white, with PNP is red.

    The red slope is a little higher than I expected. Alos input current is -3mA with VOUT at 32V. ~30V/10k = 3mA

    Here is V+ vs VOUT

    The PNP did not work with the switch open. This make sense because inverting > non-inverting with or without PNP.

    So, there is still room for improvement

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Ron,
    The plots look good.

    What is the input current of -3mA you mentioned in your last post?
    I don't understand your comment regarding the switch and inverting vs non-inverting. The switch changes the gain of the amplifier. The pnp doesn't change the amplifier from non-inverting to inverting. What do you mean by this comment?

    Where do you think the steep slope comes from? Do you see any harm in using 1M and 24k instead of 100k and 2.4k resistors to lower power dissipation and current?

    Are these plots from simulations or actual hardware?


    Does phase margin of 74 degrees would mean the circuit is somewhere between critically damped(67 degrees) and totally overdamped(90degrees)?
  • In reply to Dave Knight:

    Dave,

    Some of the slope does come from the feedback path. I used 2n3906 as the VCC diode [EB,C I should have left emitter open) ]at it leaked 2mA at 32V so using a real diode will save current that too.

    If PNP pulls non-inverting input high then that will fight input signal, that's why 3mA.
    If gain select switch is open then inverting input is almost same as OUTPUT force (32V). Non Inverting will be less voltage even with PNP turned on.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Dave,

    I increased resistors by 10X and now have better result for gain set to ~2. I added a NPN and diode to get good result for gain set to ~1.

     

    Here is the circuit as tested. (I simplified / modified some components for my testing)

    8688.opa2170 analog output(with high voltage input reversal) (2).TSC

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Ron, what is the purpose of the npn? I see that it changes the gain of the opamp, but I don't see why this is desirable.
    Why is D1 added?
    I'll try building this myself. I'm hoping to gain your insight into the circuit.

    Have you noticed that TINA shows the OPA170 sinking 21mA and 20mA flowing into the ground terminal of the OPA170?
  • In reply to Dave Knight:

    Dave,

    This is the third time that I have said that having a gain near 1, will result in IN- > IN+ so output will not go high, so there will be no reduction in output current. The diode keeps R9 and NPN from affecting the input voltage to IN+ (during normal operation). All of this will become clear after building the circuit. I have not looked deeply into the reason that it doesn't simulate as low current at 32V

    This was a fun project.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).