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OPA2834: Regarding OPA2834 application

Caliber
Intellectual 815 points
Part Number: OPA2834
Other Parts Discussed in Thread: OPA2387

Dear TI team,

Good evening.

We have requirement in which,we need to sense and measure -30V and +30V.

So we are using OP2834 for this application.

Kindly find the attached circuit.Where we have used 1.13 reference voltage to measure negative voltage.

is below circuit is correct implementation?

Thank you,

Caliber

  • 0
    Guru 140200 points

    Hi Caliber,

    the phase margin is rather low:

    caliber_opa2834_1.TSC

    If the customer insists in the values of R120 and C19, the phase margin cannot be improved drastically. Maybe to 50° with dual feedback circuit but not much more.

    Maybe I'm wrong, but I have no good feel with this circuit. I think the OPA2834 is just an order of magnitude too fast for that job with this high R120 and C19. I would go for a slower OPAmp.

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 24325 points

    Hello Kai and Caliber,

      Thank you for the in-depth simulation Kai! 

      It is a correct circuit implementation, but as Kai said there is concern for stability right at 45 degrees. This is still considered stable, but with added parasitic from board layout, it could lead to potential instability. It is possible to compensate for this issue by adding a DNP resistor between the two inputs of the amplifier which can be tuned during testing. This essentially increases the noise gain across all frequency.

      Like Kai said, there is a large filter which suggests very low frequency band. I have moved this thread over to precision amplifier team for their inputs. 

    5582.OPA2834.TSC

    Thank you,

    Sima 

  • 0 in reply to kai klaas69
    Intellectual 815 points

    Dear Kai,

    Good afternoon.

    Thank you for explaining and sharing simulation.

    Thank you,

    Caliber

  • 0 in reply to SimaJalaleddine
    Intellectual 815 points

    Dear Sima,

    Good afternoon.

    Thank you for valuable inputs and simulation.

    We are looking forward for suggestions and inputs from your precision amplifier team.

    Thank you for taking interest and escalating to your team.

    Thank you,

    Caliber

  • 0 in reply to Caliber
    TI__Guru* 93105 points

    Hi,

    There are a number of low-voltage Precision Op amps that might be applied in this sense application. It's not evident what levels of precision are required for the application, or what sort of current budget it has. What is evident is that the circuit doesn't need the speed and bandwidth of a High-Speed Op amp such as the OPA2834. With a bit more information a best match can be found.

    For starters, have a look at the OPA2387. It offers high precision and moderately low operating current:

    https://www.ti.com/lit/ds/symlink/opa2387.pdf

    Let us know your thoughts.

    Regards, Thomas

    Precision Amplifiers Applications Engineering