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INA220: current value

Part Number: INA220

Hi team,

I have some questions in below for the INA220.

1. For the INA220, the shunt voltage LSB is 10uV (in datasheet 7.5 DC acurracy).

So the current LSB* Rshunt should be bigger than 10uV?

2. In Configuration Register about ADC Settings (SADC [6:3]), not really understnd for this.

If SADC [6:3]= 0000, does that mean current_LSB should be changed to: max expected current/(2^9) ?

I don't know what's the difference for mode/sampling for 9-12 bit and 2-128 samples?

And not understand if I choose 9-bit mode, what's the impact?

Thank you!

  • Hi Zoe,

    I have received your question and will respond today.


    Thank you for your time,
    Manuel Chavez
  • Hello Zoe,

    Thanks for reaching out on the forum. The LSB value should give you a shunt value of 10uV or higher. Otherwise the signal will be lost in the noise. If I use the following procedure, I can get a current LSB that will yield a minimum vshunt value close to 10uV. For my example I assume my max current is 5A and I am using the PGA/3 setting, then my current_LSB = 0.000153 and the shunt value that allows me to use the full sensing range is 64mohm. The product of the LSB and the shunt will be a bit smaller than 10uV (9.8uV).

    Current_LSB = Max current/(2^(ADC bits) * 2^(Gain Bits))=5/(2^15)=0.000153A

    So for SADC 9 bits, PGA/3, current_LSB=5/(2^(9)*2^(3))=5/(2^12)

    As for the ADC samples setting, this corresponds to how many 12 bit measured values are averaged.

    The impact of the 9-bit mode is faster conversion time with less precision.
  • Zoe,

    1. The ADC’s LSB voltage is given to provide resolution information for signal conversions. The current_LSB parameter scales those 10µV to a useful resolution for your measurement, calculated with equation 2 on page 12 of the INA220 datasheet:

      current_LSB = max expected current / 2^15

    2. Bits 3-6 of the configuration register adjust the ADC settings for shunt voltage measurements. The adjustable settings here are ADC resolution (9-bit to full 12-bit) and averaging (1x – 32x) which affect conversion time (84µs – 17.02ms) as shown in the table below.



    • Configuration register bits 3 – 6 are displayed above as ADC1 – ADC4 respectively. If these bits = 0000, the INA220 will operate with 9-bit resolution where conversions complete after 84µs. If the bits = 1101 where bit 6 is on the left, the device will average 32 samples for each measurement, completing conversions after 17.02ms.

    These different modes offer conversion times dependent on what you need in a system. If resolution is preferred over speed, 11-bit or 12-bit settings might be your choice. In noisy environments averaging could be preferred for steady measurements.

    I hope to have been helpful! Thank you for your post here on E2E.

    Best regards,
    Manuel Chavez