Current measurement

Hello Shlomi,

Thank you for your question.

My first observation is that the current you’re trying to measure is very small.  Assuming that 20uA is your minimum load current & your current shunt monitor’s Vos(max) is 35uV, you would need a shunt resistor of at least 17.5ohms to generate a sense voltage of sufficient size for your accuracy requirement.

One thing to keep in mind, though, is the maximum expected load current.  You need to ensure that the output does not rail. 

That said, here are some additional questions that will help in selecting an appropriate current-sensing solution:

a)      What is the common-mode voltage?

b)      What is the range of current you’re sensing?  Is 20uA the minimum load current?

c)      Do you have a preference with respect to high or low-side sensing?

d)      Is this a uni or bi-directional current?

e)      Do you have any frequency concerns?

f)        Do you have a preference for the output (e.g. voltage, current, or digital)?

Shlomi;

Do not overlook using an instrumentation amplifier (IA) to measure the voltage drop across a shunt resistor. Current shunt monitors and difference amplifiers all have their place but the accuracy of a true IA is unsurpassed.