This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

> 0uA Current Detection Presence

Other Parts Discussed in Thread: INA190, INA191, INA186, INA333

After working on this for a few days I need some ideas. I have a 3.3V load that can vary from 10uA to 150mA when plugged in. I can't afford more than .1V drop in the sensing circuit and need a 3.3V signal to indicate => 10uA to the load. I am not trying to measure the current, just the presence of =>10uA (>0uA also works). Any ideas greatly appreciated! 

  • Hello Alan,

    Thanks for the question.

    If you want to detect a condition of load current > 10uA, then you will want to narrow down how this detection happens. So would you prefer it to be analog (comparator output changes) or digital (firmware  making a decision on data from ADC)?

    Overall, using a high-input impedance current sense amplifier (such as INA186, INA190, or INA191) will easily provide a way to accurately amplify the load current signal and drive this signal into a comparator or ADC.

    There is one tricky system requirement here which is the max 100mV shunt voltage drop. For a max load of 150mA, this will limit the shunt resistor to 100mV/150mA = 666.667 mOhm.

    With a shunt resistor of 666 mOhms, this means the shunt voltage at 10uA will be in single digit uV and this is already less than the max input offset of the amplifiers listed. All of this means you would need to choose a way to negate this offset error. I would recommend choosing a current sense amplifier with a REF pin (INA186 or INA190) and then perform a system calibration with ADC and firmware. The reference voltage biases the output voltage up and into linear range, the ADC reads output when load =0A, and then stores this value in memory as the starting point.

    Hope this make sense.

  • Hi Peter, thank you for the quick responses and good question. I am looking for an analog (comparator output) solution. Your analysis is spot on. For an analog solution it sounds like I manually adjust the REF pin value to get "0A", please supply the steps needed. Also, how do I deal with the small amplifier output voltage into the comparator, please suggest one? Sounds like I'll need a DC offset?

  • Hey Alan,

    There are a lot of options for comparators including some with internal references sources, which you could potentially use for INA186 REF pin. It may depend upon your budget what you choose. As long as you choose a comparator with a small enough offset, this will allow you to drive just the differential output signal into comparator with low error. Also to reduce comparator offset error, I would recommend using the highest gain variant of INA186 (500V/V). You will probably want the comparator and INA186 to share the same reference voltage too.

    Overall you shouldn’t need to tune any reference voltage for calibration. You simply need the reference voltage to be high enough to bring INA186 into its linear region of operation (~100mV to ~Vs-50mV), but not too high where the output signal is slammed into supply rail (Vs) during 10uA condition.

    If you need more gain from the shunt sensing stage, you may consider an instrumentation amplifier such as INA333, but you will need to ensure that you don’t violate any common mode limitations that current sense amplifier like the INA186 don’t have.