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Original question:

INA186-Q1: INA186-Q1 setting time

INA186-Q1: Impedance

Beida Song
Intellectual 790 points
Part Number: INA186-Q1

Tool/software:

Hi Expert,

Customer wants to know the input impedance of IN+, IN-, which is not displayed in data sheet. Can you give a support?

what does the impedance consists of?

  • 0
    TI__Expert 7160 points

    Hi Beida,

    I'm not sure if the customer is enquiring about the input impedance of IN+/- pin to GND or the differential input impedance (Rdiff) that is present within the device as shown in the diagram below.
    Rdiff is typically around 2Mohms or between 4-5 Mohms as shown in the graph below. A1 - A5 being different gain values.

    The impedance of the pin with respect to GND can be calculated as follows:

    R = Common mode voltage / Input bias current = Vcm / Ib = 12/(0.5nA) = 2400 MOhms.

    Since these are devices that are connected to a DC supply, you can consider the impedance to be purely resistive.

    Best,
    Mallika Senthil

  • 0 in reply to Mallika Senthil
    TI__Intellectual 790 points

    Hi Mallika,

    Thanks for your update.

    Customer is asking the input impedance of IN+/- pin to VCC, which is found in data sheet. Can you give a support for the impedance value and calculation process?

    The IN+/- input structure to VCC is BJT or CMOS?

  • 0 in reply to Beida Song
    TI__Expert 7160 points

    Hi Beida,

    The calculation would be the same as in my previous post. Take the voltage on the line IN+/- is connected to and the bias current at the input (Ib = 0.5nA), then use Ohms law to calculate the impedance.

    Best,
    Mallika Senthil

  • 0 in reply to Mallika Senthil
    TI__Intellectual 790 points

    Hi Mallika,

    I didn't see the electronic path from IN+/- to VCC, so I am confused on your guidance. Why bias current can be used to calculate the input impedance?

    If Vs = 5V, IN+/- = 24V, can you give the calculation process for impedance between IN+/- and VCC?

  • 0 in reply to Beida Song
    TI__Expert 7160 points

    Hi Beida,

    The connection path your referring to is internal to our device and is TI intellectual property. All customer relevant information is specified in the datasheet.

    Best,
    Mallika Senthil