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Part Number: INA220
I understand that by using the Vshunt voltage ( Vsense) with my max current load (10mA) I can determine what my Rshunt value in my design should be. However, can you explain why I might want to use the lower Vshunt voltages? It seems like with a fixed bit resolution and my current load, there will be a fixed resolution in terms of Current/Bit based on that. I know that based on Vshunt and the range of currents measured, this will attribute to the resulting error of the measurement as the lower end of voltages will have the most error and will decrease as I approached the max Vshunt voltages. How does this fit in if I need to measure a minimum step size of 0.1mA and nominal currents of 6mA. Should I choose a Vshunt voltage that is closer to the currents I will measure nominally or the smallest current I need to be able to measure i.e. 0.1mA? Thanks.
Typically the shunt should be sized smaller enough such that the shunt voltage resulting from the max current is still within measurement range. At the lower end, it should be large enough that the resulting % error is acceptable to your application. The ideal selection is somewhere in between. There has to be trade-offs between current range and % error. A 2-decade current range is manageable but fairly large.
The absolute value of the load current needs to be considered as well. A 0.1mA load current is a few times that of input bias current (IB). Therefore the error due to IB becomes more pronounced at the lower end (20%).
Please check out this video series where topics on shunt selection, error analysis are discussed among others.
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In reply to Guang Zhou:
I assume your issue has been resolved, and will close this thread. Otherwise please let us know.
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