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INA239: Queries

mudit mittal
Prodigy 50 points
Part Number: INA239

Tool/software:

Hii,

we are using INA239 for our project, following are the specs.

Current Measure : 450A

Rshunt : 100uOhm

following are some queries

1. If we are not using VBUS pin ,can it be left floating

2. The INA239 freezes if we measure current more than 50A

3. The shunt is busbar type ,the distance betwwen INA239 and shunt is more than 20cm how can mitigate the effect of harness drop,will extra filter helpful

4. we are powering INA239 using 3.3V is that effect the IC performance

Regards

Mudit Mittal

  • 0
    TI__Expert 3115 points

    Hi Mudit,

    1. Yes, you can leave Vbus floating.

    2. Can you verify the value of your SHUNT_CAL register please. It should be 1125 (decimal), but if you accidently programmed 125 (decimal) then you will be capped at 50A.

    3. To minimize the harness drop you need to find ways to lower resistance across the wires. However, since we are measuring differential voltage as long as the wires are symmetric the drop across both should be the same and therefore your differential voltage measurement will be the same. Adding filter resistors will make the drop worse, but you can add a filter capacitor.

    4. Powering the INA239 at 3.3V is fine. Our Electrical Characteristics table in the datasheet is specified for when the supply voltage is 3.3V.

    Let me know if you have any further questions.

    Best,

    Holly

  • 0 in reply to Holly R
    Prodigy 50 points

    Hi Holly

    for the current of 500A and shunt of 25uOhm , the shunt calc register value should be 312(decimal) , is the value is correct pls verify

    also i have 10ohm series resistor at IN+ and IN- pin as Rprotect, do i need to increase / decrease the value for my configuration.

    Regards

    Mudit Mital

  • 0 in reply to mudit mittal
    TI__Expert 3115 points

    Hi Mudit,

    The value in SHUNT_CAL at 500A and a shunt of 25uOhm is 312, you are correct.

    A value of 10ohms is ok on the IN+ and IN- pins.

    Best,

    Holly

  • 0 in reply to Holly R
    Prodigy 50 points

    Hi Holly

    with the shunt of 25uOhm , we are getting a error of more than 10% error in current measurement ,if we flow a 1A current along the 25uOhm shunt the measured voltage drop along shunt is .025mV while INA 239 is measuring .06mV

    i am using adc range of 163.84mV ,128samples for averaging,4120us conversion time

    Regrads

    Mudit

  • 0 in reply to mudit mittal
    TI__Expert 3115 points

    Hi Mudit,

    With the setup that you have it is normal to have this error at 1A. I am including a picture from our error calculator tool and I will link it here as well.

    https://www.ti.com/tool/CS-AMPLIFIER-ERROR-TOOL 

    If you increase your shunt resistor you will be able to get lower error at 1A. For example, at 364uOhms the error at 1A is 2%:

    Regards,

    Holly