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OPA625 input bias and offset current in SPICE model

Alexander Slepoy
Prodigy 20 points
Other Parts Discussed in Thread: OPA625, TINA-TI

According to OPA625 datasheet the nominal input bias current in High-Drive mode is +2uA, and the input offset current is 20nA. While simulating the SPICE model of OPA625 in TINA-TI I've noticed that the input bias current is being +2uA into the positive input and -2uA into the negative input. This makes the input current to be 4uA, which is in direct contradiction with Ibias and Ioffset values defined in the datasheet. Seems like a problem in the model, but I would like to be sure. The device is being simulated in the same conditions defined in the datasheet:  V+ = 5 V, V– = 0 V, MODE pin connected to V– pin, VCOM = VO = 2.5 V, gain (G) = 1, RF = 1 kΩ, CF = 2.7 pF, CLOAD = 20 pF, and RLOAD = 2 kΩ connected to 2.5 V.

Please let me know if the problem is in the model, the datasheet or in my understanding.

Thank you

  • 0
    TI__Genius 15410 points

    Hi Alexander,

    The issue seems to be within the model, I too would expect ~2uA flowing into each input of the model and the Input Offset Current being around 20nA. Thank you for infoming us of this.

    If you are interested in learning more about input bias current, I recommend checking out our TI Precision Lab videos on Offset Voltage and Input Bias Current.

    -Tim Claycomb

  • 0 in reply to Tim Claycomb
    Prodigy 20 points
    Hi Tim,
    Thank you for the advice. I've noticed another issue with the existing OPA625 model: the overload recovery times are much higher than what is specified in the datasheet (~300us vs. 35-50ns). I don't know if typically the model is supposed to reliably mimic this feature, but it caused a lot of confusion in my simulation.