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OPA4170-Q1: Input current in simulation

Prodigy 150 points

Replies: 3

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Part Number: OPA4170-Q1

I recently tried running a SPICE simulation using the model for OPA170 op amp. Positive input is fed from ISO7740 device where voltage transitions from low to high. Negative input is feedback from output through 59 ohm resistor. VDD is 10V. Load is RC divider using 59 ohm resistor and 0.22uF cap. At the transition, the simulation shows ~28mA of input current on the positive input and a similar current out of the op amp on the negative input.

Am I being had by simulation? 28mA exceeds rating for input current and it doesn't seem to make sense that the op amp would source 28mA out of the other input pin. What am I missing?

  • Hi William,

    the OPA170 has a protection circuit between the inputs. See section 8.2 and figure 38 of datasheet. When you read section 8.3.3 of datasheet you will find the following passage:

    william_opa170.TSC

    Kai

  • In reply to kai klaas69:

    Kai, thank you! I missed that note when I read through the datasheet.

  • In reply to kai klaas69:

    Hi Kai,

    Thank you for the help!!

    -Tim Claycomb

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