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Currently we are evaluating the LMP8645 as a current monitor, so far the IC performs quite good but we have a question.
Since the IC seems to be very accurate we want to sue it to measure voltage as well, we think it can be done if Rsense is placed between GND and Vin. The only problem is the Vsense voltage since it will be quite high, 12V or more since our application is to measure a 12V lead acid battery current and voltage.
I want to know if our idea can be done, we are thinking in make a design as the one showed in the picture attached, roughly the idea is use a 1M resistor (660K + 330K + 10K) connected between Vin and GND, then use the 10K as Rsense. For a maximum Vin of 15V the current flowing through the resistor network should be 0.000015A, then Vsense should be 0.15V (0.000015 A x 10.000). Using a Rgain of 110K will produce a 3.3V Vout for a 0.000015A current.
Our application also need to measure charge and discharge current from the battery, this is preform using two LMP8645. We have two options to evaluate, A and B, as you can see the difference is either use a individual Rsense or share it, If we share it then the resistance added will be decreased from 20mOhm to 5mOhm. the only problem that I see here is the Vsense, it is just 10mV at maximum range and the spec file says the best performance is obtained when Vsense is between 100mV and 200mV.
I would like to know your comments about this two options.
Wait for your comments.
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