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LMP8640: What is the minimum current sensing?

Part Number: LMP8640
Other Parts Discussed in Thread: INA293, INA190, INA186

Hi !

What is the minimum current sensing in the attached circuit?
Can you detect a current of 1[mA]?

Thanks for the answer.

  • Hi Gwanwoo,

    a worst case input offset voltage of LMP8640 of 1.2mV means an error current of 0.24A with respect to your 0.005R shunt :-(


  • Hi !
    Thanks for the answer.

    I have 2 additional questions.

    1. It should detect current from 0.1mA to 4A.
    2. It should detect current from 0.1mA to 0.4A.
    Do you have any recommended solutions?
    I hope the recommended solution is similar to the LMP8640.

    Thank you.

  • gwanwoo, 

    Measuring down to this amount of current with the LMP8640 will be challenging because of the offset voltage that Kai mentions above. You can set the shunt such that it maximizes your full scale range to help, but this will still see significant on the lower end. You can do that here by looking at the full scale range of the device, and working backwards to the shunt. So, for example, examining the G=20V/V variant, and a Vs of 5V, if the maximum output of the device is 4.95V, then dividing by the gain, we see that the maximum input sense voltage is 247.5mV. So for a 4A measurement, the maximum shunt we could choose is 61.8mΩ. Obviously this value of resistor does not exist, so I'll choose the next lowest standard value of 56mΩ. This value would maximize my measurement range, but with the 1.2mV offset over temperature that Kai mentions above, at 100mA, the generated sense voltage is still only .1A*.056Ω= 5.6mV, which means the 1.2mV offset is injecting 21% error into my measurement.

    Do you need precision at the lower end of your measurement scale? If so, can you share what you like about the LMP8640? Perhaps I can recommend a device with a better offset voltage for additional accuracy at the lower end of this range. 

  • Hi!

    Thanks for the answer.

    Please recommend another better solution.

  • gwanwoo,

    given that this is a higher BW part, I would recommend having a look at the INA293. I placed your desired range of measurement into our error calculator on the INA293 product page, and rendered the below curve. Using the same scenario I discuss above, you can see that this device exhibits <1% error for the full range you mention. If this is an acceptable error margin, then it should most likely work for both of your above sensing conditions:

    If you do not need the bandwidth, I would also recommend having a look at INA190 or INA186.

  • Thanks for the answer.