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INA199: Current taken by the power supply to the INA199

Part Number: INA199
Other Parts Discussed in Thread: TLV1701, , INA186

With a larger sense resistor like a 10 ohms used with the INA199A2, should we expect a larger amount of current being taken at the power supply pin when the current being sensed and therefore the voltage across the 10 volts is higher? The power supply is around 3.1Volts. 

The output is connected to a high impedance like the input of a TLV1701 comparator.

  • Ashvin,

    You should not see a large increase in power supply.  Be aware that your input bias current is about 28µA so there could be an error associated with that.

  • Hello,

    To be specific, these are the parameters:

    1. Supply voltage where the current is to be sensed: 6.3V

    2. Sense resistor 10 ohms, 5.1 ohms also gives a similar result

    3. Current passing through the sense resistor is 1mA to 20mA.

    4. Current drawn from the power supply @ 3.1V = 100uA @ 1mA, but it is around 1 amp at 20mA.

    5. If the sense resistor is changed to 0.8 ohms to 1 ohms, then this much of a change in the supply current is not noticed and it is around 10 to 20uA only.

  • Sorry point number 4 should read 1mA instead of 1amp.

    So could any other change in the test circuit explain this increase in current at the power supply at 20mA with a higher sense resistor than a lower sense resistor?

    Thanks,

    Ashvin.

  • Hi Ashvin,

    is it the current drawn by the whole circuit (including the INA199) or only by the INA199 itself?

    Kai

  • Hi Kai,

    The whole circuit consists only of a INA199A2 (gain 100) or INA199A3 (gain 200). There is no load at the output of this.

    The 1mA is consumed only by the INA199A2/A3, only when the 10 ohms is used as a sense resistor and a current of 20mA is passing through this 10 ohms.

    The question is this increase in supply current expected when the sense resistor is as high as 5 ohms or 10 ohms?

    Thanks,

    Ashvin.

  • Hi Ashvin,

    could it be the output current of INA199 into the load resistance?

    Can you show a schematic?

    Kai

  • Ashvin,

    I looked into it some more and found out that if you overdrive the inputs to create the output above the supply rail it will cause the supply current to increase just like you have seen.  This is operating the part outside of the linear range.  The best way to avoid this is to limit you input to Voltage Supply/Gain.  In your case you could increase the supply voltage to the 6.3V of your supply but you will still be limited to 6.3V/200 if you use INA199A3 version.  You could also drop your Rshunt value like you mentioned.

    We do have newer parts like the INA186 which might be a better option for you application as the input bias current is in the nA range vs µA range of the INA199.  The output is better with the output saturation as well.  It is also a drop in replacement if you are using the SC70 pakage and would like to try it in your circuit.