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INA210: Current Sense Amplifier Suggestion - High Dynamic Range

mithun swamy
Prodigy 155 points
Part Number: INA210
Other Parts Discussed in Thread: TIPD129, OPA320, , INA213, INA138, INA139, INA225, INA169, INA168

Hi,

Our application requirement is as below and we are in need of a Current Sense Signal Conditioning/Amplifier for this. 

Requirements-

Current Range - 1mA to 30A

Resolution - 1mA

We are using low side current sense for this  as high side will lead to high common mode voltage. We plan to use a current sense resistor of 25mOhm to counter lowest current measurement. Doing the math for 1mA to 30A will lead to a voltage drop of 25uV to 750mV across the sense resistor.

1. Can you suggest a suitable Current Sense amplifier/conditioning to measure this differential voltage across the resistor?

2. Also, even with a highly precision Opamp, offset voltage tends to be in order of tens of uV. Our lowest measurement might me well below this offset voltage. Will this impact our application considering we will be calibrating this system before its use to nullify the offset error? 

3. Are instrumentation amplifiers are required for this application or can this be achieved using a precision Current Sense?

Regards,

Mithun

  • 0
    TI__Genius 17990 points

    Hello Mithun,

    I think you might be able to adapt the TI design TIPD129 (http://www.ti.com/tool/TIPD129) to your application. Will this work for you? 

  • 0 in reply to Mitch M
    Prodigy 155 points

    Dear Mitch,

    Thanks for your feedback. 

    This reference design uses OPA320 precision opamp with a low noise and low offset voltage. One additional point to note is the use of a negative rail to not saturate low current outputs. But with this design, current is not measured deferentially. The path from Current shunt ground to opamp ground is long and any parasitic will add additional resistance and its affect on higher currents is even worse.

    Also, this additional parasitic resistance depends on temperature because of which even if system is calibrated with this parasitic is mind, its performance will become temperature dependent.

    With this in mind, do you still suggest to use this Opamp or use any differential Current Sense?

    Regards,

    Mithun

  • 0 in reply to mithun swamy
    Prodigy 155 points
    Hey Mitch,

    Any feedback from your side?

    Mithun
  • 0 in reply to mithun swamy
    TI__Genius 17990 points
    Hello Mithun,

    I am still looking into your question and checking out your options. I will get back to you as soon as I can.
  • 0 in reply to Mitch M
    TI__Genius 17990 points
    Hello Mithun,

    I am still checking on some options for you, but I see what you are saying about the OPA320. For now it looks like the INA210 could work for you. The maximum offset is 35uV, which won't work for your specifications, but the majority of that could probably be calibrated out for each device if you have a consistent system.
  • 0 in reply to Mitch M
    Prodigy 155 points
    Dear Mitch,

    INA210 seems alright, except for the gain. Its minimum gain in this series which is INA213 is 50V/V. As said earlier with a 25mOhm resistor, voltage drop across it without any gain for maximum current of 30A is 750mV.

    If we have to use INA213 I will have to use a resistor of around 1mOhm. This translates to following.
    1mOhm - Maximum Voltage Drop - 30mV - After Gain Voltage will be 1.5V.

    But at minimum current of 1mA, this translates to a voltage drop of 1uV. Though this translates to a voltage of 50uV at the end of the OPA213, I am skeptical if we can achieve this practically. Even with a very small track resistance, these voltages might not even reach ADC input. Also matching the exact resistor which gives a full scale ADC voltage range is also a challenge with fixed gains.

    Also, is there any Current Sense Amplifier with unity gain. I know it does not become a amplifier then, but a signal conditioning unit to convert differential signal to single ended signal. But this should also do the job for us.

    What do you think about my above point of view?
  • 0 in reply to mithun swamy
    TI__Genius 17990 points

    Hello Mithun,

    I see what you are saying. We do have some unity gain Current Shunt Monitors, the INA138, INA139, INA168, and INA169. Also, you may want to look into the INA225, which has a programmable gain that can be used with a microcontroller to change the gain dynamically. If none of these work for you to get the resolution you need, then a discrete solution may be best. If that is the case, let me know and I can move this conversation to the Precision Amplifiers forum so that they can help you find what works for you.