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INA220: Parameters of INA220A

Intellectual 940 points

Replies: 2

Views: 121

Part Number: INA220

Hello Team, 

One of my customer is looking for following parameters of INA220A sensor. Can you please suggest. 

  • Switched capacitance of an analog input
  • Resistance of the analog input path
  • Programmed gain
  • Gain drift after calibration
  • CSA input bias current
  • CSA input offset current
  • settling time of the OPAMP
  • CSA Input resistance

Regards,
Naveen

  • Hello Naveen,

    Im looking into your question now. I need to run some of your questions past people in design and therefore it may take a day or so to get back to you.

    Best Regards,

    Patrick Simmons, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your 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 your designs.

  • In reply to Patrick Simmons:

    Hello Naveen,

    When you say switched capacitance of an analog input, it makes me think of the front end of a SAR ADC that has a switched capacitor for sample and hold measurements. If this is what you are implying, then it does not apply to the INA220 as it is not a SAR architecture but rather a delta sigma architecture.

    For the input resistance and analog input path resistance, can you clarify what you mean and what you hope to achieve with that information? I presume your customer is thinking he can modify the gain with an external resistor that is assumed to be simply in series with one of the gain setting resistors of the internal amplifier. Typically that is not advised for any of our devices as those with a front end difference amplifier have their resistors trimmed ratio metrically with the ratio having low tolerance while the individual resistor might have a tolerance of 15 to 30%. In addition to the high tolerance in the resistors, our parts typically also have a front end common mode sense circuit which means there is another circuit branch that feeds into the node between the external resistor and the internal gain setting resistor. These two items typically complicate a simple modification of gain and we will therefore typically provide a gain error equation when relevant. However, for this part we don’t provide that equation, because the front end is not a difference amplifier but rather a delta sigma ADC.
    The PGA setting of the INA220 corresponds to the number of bits used in the ADC register. The LSB of the INA220 is ~10uV for all PGA settings. In the datasheet table PGA = /8 corresponds to 15 data bits and 1 sign bit. Each subsequently smaller Full-scale current sense (input) voltage range has one less data bit or a smaller MSB.
    For example:
    PGA = /8, 15 bits used : 0.320V/(2^15)=~10uV
    PGA = /4, 14 bits used : 0.160V/(2^14)=~10uV
    PGA = /2, 13 bits used : 0.080V/(2^13)=~10uV
    PGA = /2, 12 bits used : 0.040V/(2^12)=~10uV

    The gain error over temperature is 1 m%/ᵒC. The calibration procedure provided in the datasheet modifies the output scale.

    The CSA input bias current oddly place under the IN+ and IN- pin input impedance specification of the datasheet. Here both input bias currents are typically around 20uA. Defining input offset current as (IB+)-(IB-) therefore yields 20uA-20uA = 0. While it is probably not 0, its still something comparatively much smaller.

    With respect to the settling time, it depends upon the accuracy you want to have. 9-12 bits of accuracy ranges from 84 to 532us and these values can be found in the electrical characteristics section of the datasheet. Each extra bit of accuracy corresponds to an order of 2 averaged conversions. For instance 13 bits corresponds to 2 conversions, 14 bits corresponds to 4 conversions, and 15 bits corresponds to 8 conversions. The remaining averaging options are for removing noise that may be present in the system.

    Best Regards,

    Patrick Simmons, TI Sensing Products Applications Support

    Getting Started with Current Sensing Video Training Series

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your 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 your designs.

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