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Wide range current sense 0.1uA - 500mA

Paul Antunes
Intellectual 2590 points

Other Parts Discussed in Thread: INA209, TIPD104, INA326, TIPD135, PGA281

I have a new request from industrial key account.

The desired current range for customer application is given as 0.1uA to 500mA.

Supply voltage is 5V, signal to sense is quite slow (us to few seconds).

Do we have a circuit to recommend for such application ?

thank you in advance for your support.

Paul

  • 0
    Prodigy 10 points

    Need a recommendation for a current sense amplifier (using resistor shunt) but the following requirements are:

    • High side
    • 5V USB supply
    • Detect current ranges from nA to mA
    • Interface with external MCU adc

    Any help on this would be greatly appreciated as i am fairly new to all of this

  • 0
    TI__Genius 15770 points

    Hi Andrea,

    Thanks for reaching out. Our current sense amplifiers are not able to detect current in the nA range. The input bias current of our devices is significantly higher than nA's.

    I am going to move your question to the precision amplifiers group. They might be able to recommend one of their devices.

    Regards

  • 0
    TI__Guru**** 174826 points

    Andrea,

    What is the needed accuracy for each current flow decade (or some other separation factor)
    This will let me know if multiple amplifiers are needed and maybe multiple shunt resistors
    It would also help to know why such a large range is needed.

    1 to 10nA = xx%
    10n to 100nA = yy%
    and so on. (or you can pick your own divisions)

    Would a logarithmic amplifier be acceptable?

  • 0 in reply to Ron Michallick
    TI__Intellectual 2590 points
    Hi Ron,

    I have similar request from industrial key account.

    Customer would sense current in range 0.1uA - 500mA. He plans to use different shunt resistor to get the accuracy needed for his application.
    Supply voltage is 5V and signal to measure is in window between micro-second and few seconds.

    Which opamp do you recommend for my customer ?

    Customer has identified INA209 but not sure this part fit his use case. Leakage current on input pins of INA is 0.1uA typ which is the min current customer wants to sense.

    thank you in advance for your support.

    regards,
    paul
  • 0
    TI__Mastermind 25875 points
    Hello Paul,

    We do not have a reference design for such a wide range of load current. 100nA to 500mA represents >6 decades of load current. The customer will require a PGA and/or shunt resistor switching network. Here are a couple Precision Designs that will give them an idea of how it may be accomplished:

    TIPD104: This TIPD uses the INA326 on the low side. There is a switch that changes the gain of the device once, which allows for the sensing of 3 decades of load current. Please note that this Precision Design was only simulated.

    TIPD135: This TIPD uses the PGA281 on the high-side to sense 4 decades of load current (10uA-100mA). It is supplied with +/-15V.

    One additional important factor when dealing with very small load currents is the input bias current of the amplifier (in addition to the offset voltage). Make sure that the input bias current is much smaller than the load current. In addition, please note that the PCB layout of switching shunt resistors may be difficult. If they choose this path, make sure each shunt is Kelvin-connected to the amplifier and that the switch's on-resistance does not affect the measurement.

    I hope this helps!
  • 0 in reply to Paul Antunes
    TI__Mastermind 25875 points
    Hello Paul,

    Looks like there are multiple threads here, so I will merge this one with the thread that I replied to.
  • 0 in reply to Pete%20Semig
    TI__Intellectual 2590 points
    Pete,

    Do you recommend INA326 or PGA281 to sense small current like 0.1uA? if not, which circuit better fit customer spec ?

    TI design you have recommended as reference are designed for 10uA.

    thanks
    Paul
  • 0 in reply to Paul Antunes
    TI__Mastermind 25875 points
    Hello Paul,

    Both of those devices have maximum input offset currents of +/-2nA. So the bias current itself may introduce up to 2% error given a 100nA load current.

    I recommended those reference designs as examples for the customer that show how to change gain discretely or with a PGA in order to sense 3-4 decades of load current. The customer's final solution will likely be much more complex given the extremely wide load current range.

    Note that the supply voltage vs. common-mode voltage is very important here. It sounds like the supply voltage and common-mode voltage are both 5V...is this correct?