[ measuring load voltage using minimum current ]

[texane]

Hi,

I am implementing a carrier board for the TEENSY3.1
microcontroller to measure both voltage and current
of an external DC load. With this circuit, I am interested
in seeing voltage and current transients related to load
current peaks. The MCU 2 integrated 16 bits ADCs are
used for measurements. Attached is a functional view.

To measure the load current, I use a high side shunt
resistor and a INA210 (powered by the MCU). This has
been validated, I have no questions on this part.

The external DC load voltage may be within 0 - 12V.
Thus, I will use a voltage divider to scale the voltage
before feeding it to the MCU ADC (blue path on picture).
The resistor sum is large, as I want to minimize the
current used for the measure: the DC load current resolution
is in the uA order, and I do not want to influence the
external DC load supply (a 3v coin battery typically).

Is a resistor divider well suited at all ? If not, what
do you propose ? Otherwise, I am aware that the current
used for the measure should be large in respect to the
ADC internal current. But I also want it low to not
perturbate the measure. How do you solve this ?

Thanks very much for your help !

Cheers,

f.