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Current sensing wide range low to mid current

Snir Azulay
Prodigy 10 points
Other Parts Discussed in Thread: INA226, INA190

Hi

We need to measure a device that working under different current consumption

0.1uA to tens of mA (60-100mA) 

Do you have any recommendation for components that can help to measred such wide current range

  • 0
    TI__Mastermind 21805 points
    Hello Snir,

    Thank you for considering to use Texas Instruments for your current sensing application. Our current shunt devices typically have a fixed gain, so it is unlikely you will be able to cover such a wide range with those alone. Our adjustable gain devices similarly would have problems accommodating such a range as those are typically controlled by a resistor value. However, if you absolutely need to measure this range and happen to have already a microcontroller nearby on board, you could potentially have the microcontroller toggle a FET switch that would either change the shunt resistor used or the gain setting resistor when certain output thresholds are exceeded for a given state. What kind of resolution are you trying to achieve in your measurements and what is the range of your common mode voltage?
  • 0 in reply to Patrick Simmons
    TI__Genius 16080 points

    Hello Snir,

    In addition to Patrick's comment on the range of current measurement being difficult with a single shunt/amplifier, the low-end of the current you want to measure (0.1uA)  is less than any of our current sense amplifiers can measure due to the bias current on the inputs pins of the device.  For measuring this current level, you need to look at instrumentation amplifiers that have extremely low bias currents.

  • 0 in reply to DHarmon
    Intellectual 570 points
    Hi Dan,
    I have a similar requirement of measuring 0.1uA - 25uA. There are 2 other currents I need to measure in the 1mA to 2A range with a 2-10VDC range. The feature rich devices like the INA226 seem ideal for this higher range and I'd like to have a single interface for the software. Any chance an amplified current mirror might boost the current up to a level that is workable for the the INA226 type devices?
  • 0 in reply to Mark Nohr
    TI__Mastermind 21805 points
    Hi Mark,

    Sorry for the delayed reply. Your current mirror suggestion is an interesting approach to measuring the lower currents, however I suspect it may be difficult to achieve high accuracy. A current mirror may require meticulous placement of your transistors, accounting for both manufacturing variation of the transistors and temperature variation throughout your board. However, how were you planning on implementing your current mirror? Could provide a basic schematic?
  • 0 in reply to Patrick Simmons
    Intellectual 570 points

    No problem. we are working the issue actively. I've engaged an analog engineering specialist given the sensitivity of the design. We are planning on putting a front end on to amplify the signal (probably not a current mirror). If there are any recommended approaches or pitfalls we should watch out for, I'd greatly appreciate the insight.

  • 0 in reply to Mark Nohr
    TI__Mastermind 21805 points

    Hello Mark,

    For measuring  such low currents, we do not have a current sense chip that can attain such resolution with high accuracy yet.  However, you still may be able to come to an appropriate solution through using one of TI's instrumentation amplifiers.  I would recommend reaching out to the Precision Amplifiers group on their forum here: https://e2e.ti.com/support/amplifiers/precision_amplifiers/

  • 0 in reply to Patrick Simmons
    TI__Mastermind 21805 points
    Hello Mark,

    As you have not replied in a while, your desired specifications are outside of what we can provide, and as the precision amplifier team may better assist you, I will close this thread. However, if your desired specifications change, feel free to reach out and open a new thread. Good luck on your design!
  • 0 in reply to Patrick Simmons
    TI__Mastermind 21805 points
    Hello Mark,

    I am sure by now you are far along with a design for measuring measuring 0.1uA - 25uA. However, if you're are still looking for a solution or would like to know of an alternative, our product line just released the INA190. This particular device has ultra low input bias current. To illustrate its performance we can compare it with the INA226 you previously posted about. If we look solely at the input bias current specification and assume you are using a 2mohm shunt, we see that input differential voltage at 0.1uA detection current for the INA190 would be 550pV while for the INA226 it would be 50.5nV; (sense current + input bias)*Rshunt = input differential voltage. Consequently the INA190 gives a 10% error while the INA226 gives a 10000% error; (input differential with input bias - ideal input differential)/ideal input differential *100= % Error. One thing to note though, there will still be other sources of error such as input offset voltage. However, the input offset voltage specification for the INA190 is also substantially lower than that for INA226.
  • 0 in reply to Patrick Simmons
    Intellectual 570 points

    Thanks Patrick.

    A nice front end indeed. We wound up pre-conditioning the lower range to match up electrical interface of the INA226 to take advantage of all the other features the INA226 offers. Switching horses at this point would mean a major architectural change.

    -Mark

  • 0 in reply to Mark Nohr
    TI__Mastermind 21805 points
    Mark,

    Glad to be of help. Good luck on your design, and feel free to reach out again if you have any further questions.