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INA226- pulse current measurement

Rajesh Kumar72
Intellectual 500 points
Other Parts Discussed in Thread: INA226, INA228, INA237, INA226EVM

Hi,

We are planning to use INA226AIDGSR to measure pulsing current. Current is pulsed using PWM frequency of may be 40KHz with varying duty cycle of 10% to 100%.

Is this device capable to measure average current?

Max current 50mA, with 40KHz 10% duty cycle, average current will become 5mA, will INA226 able to measure average current? If yes, how does it averages out the current, please explain.

Regards,

Rajesh

  • 0
    TI__Mastermind 26485 points

    Rajesh,

    I am not sure if this can be done and I will have to see if I can verify this.  What value do you have as your Rshunt?  This will help me determine the input voltages to model in the lab.  Also is the Common Mode of the INA226 input change with the PWM signal or not.  This will help determine if the AC CMRR input will be an issue.  The there is a large Common Mode voltage transient that may be an issue as there is no settleing time that will be synced with your PWM signal causing a spike during the measurement that is not real but an artifact of the Common Mode rejection for the analog front end of the INA226.

  • 0 in reply to Javier Contreras4
    Intellectual 500 points

    Hi Javier,

    Thanks for your prompt response.

    Rshunt is 40m ohm, and INA226 is used for high side sensing.

    Common mode voltage (BL_LED_SUPPLY) will be 28.5V +/-0.5V which is not pulsing, only shunt current will be pulsing. Below is the circuit for your reference:

    To take care of CM transient, we are planning to use a low pass R-C filter at the input of INA226.

    If INA226 doesn't meet our requirement, do you have any other current sensing device which can meet our requirement.

    Regards,

    Rajesh

  • 0 in reply to Rajesh Kumar72
    TI__Mastermind 26485 points

    Rajesh,

    What is the RC filter you are using at the input?  I will attempt this in the lab tomorrow.

    You may want to look at the INA228 it does a faster conversion time.  If you don't need that much resolution you can use the INA237.  These are new devices and our in preview status meaning you can get samples but these are not ready for production.  "Preview".

    If it does not work for the INA226 it may not work the other digital devices either.

  • 0 in reply to Javier Contreras4
    Intellectual 500 points

    Hi Javier,

    We are planning to use 2 ohm and 0.01uF RC combination.

    We would prefer to go ahead with production ready devices.

    Regards,

    Rajesh 

  • 0 in reply to Rajesh Kumar72
    TI__Mastermind 26485 points

    Rajesh,

    I attempted a 40kHz signal with a 0-2mV at the fastest conversion time of 154µs and varied the averaging but mostly 1024.  I was able to vary the duty cycle form 20% to 80%.  I placed it to only measure the Shunt voltage and the number measured as it was all valid output.

    The average improves the value. Increasing the conversion time made the value worse.

    I believe you should just attempt a INA226EVM and try it on your system.  The accuracy you need vs the configuration you can tolerate will dictate if this will work for you but the functionality has verified in my lab.

  • 0 in reply to Javier Contreras4
    Intellectual 500 points

    Thanks a lot Javier for trying out the experiment in your lab and confirm the functional validation.

    That means we shall be able to measure pulse current accurately by trying out suitable conversion time and averaging options available with this device.

    Currently we don't have INA226EVM with us, we will try to test the functionality on our proto board.

    Just to ensure, in your lab have you tried reading shunt voltage with  RC filtering or without that, please confirm.

    Best Regards,

    Rajesh

  • 0 in reply to Javier Contreras4
    Intellectual 500 points

    Thanks a lot Javier for trying out the experiment in your lab and confirm the functional validation.

    That means we shall be able to measure pulse current accurately by trying out suitable conversion time and averaging options available with this device.

    Currently we don't have INA226EVM with us, we will try to test the functionality on our proto board.

    In your lab what mode you have selected to read the values - continuous or triggered? Also, when you say all outputs were valid, does it mean that you got the shunt voltage values of 2mV each time after reading the converted values, or does it give you 0.4mV for 20% duty factor and 1.6mV for 80% duty factor. Please confirm.

    Just to ensure, in your lab have you tried reading shunt voltage with  RC filtering or without that, please confirm.

    Best Regards,

    Rajesh

  • 0 in reply to Rajesh Kumar72
    TI__Mastermind 26485 points

    Rajesh,

    Please excuse the delay as I was on holiday.

    In my lab the measurements were continuous and they did give me the values you explain above.  I did vary the averages and the small average value the output varied more.  I was only looking for it to function and it would be understood that for ~150µs conversion time you would need a few averages to get the desired average value.

    I used the RC filter you described as a 2Ω on each input pin and a 0.01µF capacitor between the inputs.

    Let me know if you are not getting similar results.

  • 0 in reply to Javier Contreras4
    Intellectual 500 points

    Thanks Javier for responding back and answering all the queries.

    We took some time to understand the working of sigma-delta ADC and with your lab results we are sure that INA226 will provide good results based on optimal selection of conv time and averaging. In real application, we may not be going for such a higher PWM frequency - it may be limited to 5KHz or so.

    We will go ahead with circuit implementation now and would like to get it reviewed by you offline. Could you please provide your email id so that we can share two circuit implemetations using INA226. Please note we are using 2 nos. of INA226 in our proto design for different applications. Is there any possibility to get the INA226 EVM for testing?

    Best Regards,

    Rajesh

  • 0 in reply to Rajesh Kumar72
    Intellectual 500 points

    Thanks Javier for answering all our queries.

    Regards,

    Rajesh