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INA214: High Side Bi-Directional Current Sense appnote, calculations, component selection

Jason Muhammad
Prodigy 130 points
Part Number: INA214

Greetings,

I could not find app note on INA214 precision high side current measurement so I used calculation example from SBOA300–June 2018 document. I wanted to know if TI can verify both I can use these guidelines (calculations) from low side document and that my calculations on attached writeup is OK. Basically I have +/-5A, VSS=3.3V so needed to decide what voltage reference, gain (ie INA21x device) and sense resistor to use. I came up with 1.8V reference, 0.002 ohm sense resistor and gain=100 to obtain 0.8V-2.8V output.

Also, is there any hysteresis with these devices when setting reference to midscale?

Thanks in advance.

-Jason.

CWB DSG_Event Calculations (using INA214).pdf

  • 0
    TI__Mastermind 26465 points

    Hello Jason,

    The calculations look correct.  The one thing I would also make sure you look into is if you have a large load on the output you will need to observe figure 10 in the datasheet.  This shows the output limitations as you increase the load at the output.  If you have the option to place any voltage on the Vref pin I would suggest you use Vs/2 = 1.65V.  The 1.8V will work but best would be VS/2=1.65V.  Note that INA214 swing high is lower that swing low.  Note(2) in table is to observer figure 10 as mentioned above.

    By hysteresis I assume you mean crossover.  This is where it crosses the zero current point.  I do not think you will have issues there.  I would make sure the frequency and bandwidth is what is required as this is where you could have more issues if the device cannot keep up with your input signal.

  • 0 in reply to Javier Contreras4
    Prodigy 130 points

    Thanks for looking this over.

    The output of the INA214 and the 1.8V reference are going into a comparator. So if discharging (.8V-1.8V) the comparator will output a logic low (0V); if charging (1.8V-2.8V) the comparator will output a logic high (3.3V). Should be 

    I don't know why the INA214 doesn't just go to an ADC and let software determine that it is charging/discharging (maybe logic levels for uC interrupt or was going to use to drive an enable pin of something else; comparator for noise immunity...I don't know) but my job is to modify an old existing design for 3.3V and higher charge/discharge currents.

    I did find a low quiescent current (5uA) 1.6V reference IC (I think this is good enough). With VREF=1.6V and RES1=3mOhms:

    DSG(0A to -5A): VOUTmin=0.1V; VOUTmax=1.6V
    CHG(0A to 5A): VOUTmin=1.6V; VOUTmax=3.1V

  • 0 in reply to Jason Muhammad
    TI__Mastermind 26465 points

    Jason,

    Offset could be your biggest issue doing this. You will need to look at the offset of both the comparator and the INA214 and the biggest contributor will most likely be the INA214 as the offset will be gained up by 100.  At room temperature under global operating conditions the max Vos  = 60µV meaning an error of 6mV that the output.  Also at low currents you will need to account for the input bias currents and this is specified at max of 35µA.  This should be an error that is much smaller than the error from VOS unless you have Resistors in series at the input.

    For your circuit with 3mΩ this will correspond to 60µV/3mΩ = 20mA current error from VOS. 

  • 0 in reply to Javier Contreras4
    Prodigy 130 points

    Greetings,

    Thanks Javier, this is good information. Is there anyway to reduce the INA214 offset?

  • 0 in reply to Jason Muhammad
    TI__Mastermind 26465 points

    Jason,

    Unfortunately not, but a bidirectional device is easy to calibrate by measuring zero voltage at the input.  Then you will mostly need to worry about changes from that point.  The way you are planning to use it may not be ideal for this calibration.  We do have some other devices that do have lower offsets but for me to give a recommendation.  I have included a link with list of devices with offset below 50µV.