Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 31 subscribers
  • Views 869 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

About the current LSB of INA219

Takamaru Akita
Prodigy 140 points
Part Number: INA219
Hi team,

Would you help my understand of the current LSB?
In the datasheet of INA219, there is the description of the shunt voltage LSB =10uV.
When using the 1mΩ shunt resister,  is the current LSB  =(shunt voltage LSB:10uV)/(shunt resister:1mΩ)=10mA?
I think 10mA is the minimum unit of the current that INA219 can recognize difference of the current, is that correct ?
In datasheet p12 , there is the equation (3) (Current_LSB)=(Maximum Expected Current/2^15).
I couldn't understand what does mean.
Does the (Current_LSB) appears in equation (3) means the recommended software value of Current LSB  for good mesurement?
Thanks,
Best Regards
Akita
  • 0
    TI__Mastermind 30910 points

    Hi Akita,

    These two approaches don’t contradict and are equivalent. The first approach starts with Rshunt and current LSB in mind; the 2nd (datasheet) starts with Rshunt and full scale current in mind.

    You just need to pick one and go with it, the end results should be identical if the selected current LSB is also 10mA in approach #2.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Prodigy 140 points

    Hi, Guang

    Thank you for your reply.

    >These two approaches don’t contradict and are equivalent.

    But it looks two aproaches are not equivalent in the datasheet application.

    [ p25-p26(Conditions:Maximum expected load current = 15 A, Nominal load current = 10 A,VCM = 12 V, RSHUNT = 2 mΩ, VSHUNT FSR = 40 mV (PGA = /1).]

    In this case, the minimum-current LSB is calculated to be 457.78 uA/bit, and it rounded up to 1mA/bit. 

    On the other hand, (Shunt Voltage LSB:10uV)/(RSUHNT:2mΩ)=5mA, and the first apprach and the second aproach looks different.

    Would you let me know how could I comprehend this mismatch?

    Thanks

    Best Regard

    Akita

  • 0 in reply to Takamaru Akita
    TI__Mastermind 30910 points

    Hi Akita,

    When LSB=1mA, the full range current=32A, and full range Vshunt=64mV; when LSB=5mA, full range current=160A, and Vshunt=320mV.

    To put it simply, the current LSB is somewhat arbitrary; it is only needed by the device for the sake of calculating the scale factor.

    When it comes to reading the shunt voltage (reg 01), there is no difference between the two. And there is no difference in actual (aka analog) current resolution. If we don’t need to read current in digital format from INA219 directly, we can simply do the calculation ourselves using Reg01*10uV/2mOhm/1000, the result is in Amps. See section 8.5.3.

    Regards, Guang