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INA199: Asking or the INA199 schematic review

SHH
Mastermind 31176 points
Part Number: INA199

Hi Team,
customer is evaluating INA199.
Would you please review the schematic and provide your comment?

The trigger voltage will be designed as 1.65V for 33mA as below calculation.

txn.box.com/.../71ikwey1ngjhn2gmfq96grhngs6xffuy


BR,
SHH

  • 0
    TI__Mastermind 24145 points
    Hello SHH,

    Thanks for reaching out on the forum. Is your customer expecting alot of common mode transients a little above 1.6MHz? I ask as the 10 ohm resistors on the input will create a gain error. This error could be as high as 100-(100-1250*20000/(1250*10+1250*20000+10*20000))=0.842836%. Excluding resistor tolerances and all the other possible sources of error, your trigger may be as low as 1.636V. Another thing you may to do is buffer the voltage divider input to the REF pin as the voltage divider can provide an additional source of error. What value resistors are you using for the voltage divider by the way?
  • 0 in reply to Patrick Simmons
    TI__Mastermind 31176 points
    Hi Patrick,
    thanks for your feedback. Could I know what would you recommended for customer case for the gain error and REF voltage divider error?

    BR
    SHH
  • 0 in reply to SHH
    TI__Mastermind 24145 points

    Hello SHH,

    If your customer does not have high frequency common mode transients, I would remove the 10ohm resistors.  If your customer's common mode transients are in the low Megahertz range I would suggest increasing the capacitor size and decreasing the resistor sizes.  As for the REF a general purpose op amp should be sufficient to buffer the voltage divider input.

  • 0 in reply to Patrick Simmons
    TI__Mastermind 31176 points

    Hi Patrick,

    thanks for feedback.

    .      There is 1.3MHZ frequency boost converter before Rsense, and plan to use current shunt monitor 120Hz/35%/10V/26mA PWM load.

    What is the cap and resistor value you would recommend?

    Customer plan to use +/-3% as our error tolerance, so consider the INA199A internal gain error max value, the theory gain error will be 0.84+1.5=2.34%.

    Is it right?
     

    2.      The resistive divider of REF is reserved if it need in the future. The high side resistor is not insert, only use low side 0ohn resistor pull to GND.

    BR,
    SHH

  • 0 in reply to SHH
    TI__Mastermind 24145 points

    Hello SHH,

    If your customer wants to guarantee a lower possible error, I would suggest a resistor smaller than 10 ohms with a bigger capacitor.  I do not have a specific value to recommend.  As for the gain error, how you calculated above would be the theoretical worst case.  A more likely error would be calculated by taking the root sum squares of 0.84 and 1.5.  Your customer should also pay attention to the tolerance of the resistors in the filter as well as the tolerance of the shunt.  Those too will contribute to the total error.   The total error your customer would expect would be the RSS value of all the error sources.  For more information on those, we discuss them in our training series.