ADC unstable reading at High current

Thread Starter

Emmanuelpeace

Joined Mar 20, 2018
3
Good Morning, Seniors
Please what could be the reason and possible solution, for my ADC measurement on the microcontroller increasing more than the actual values, when high current is going through the circuit.?
Basically, I had just designed a battery charger with interleaved buck converter and I am using the MSP430FR5994 microcontroller for the control, while the battery is charging, I am monitoring the voltage at the output. Before start of charging, the voltage being measured on the microcontroller corresponds to the multimeter, however when the device starts charging and starts drawing current of more than 2.5A, the voltage being measured on the microcontroller, is far above the one meausred on multimeter, by about 0.8V, this is not nice for me.
I have checked the ground of the device and made sure the ground of the biasing circuit runs seperately from the power electronics ground., though connected at the source gnd (in this case, solar panel).
I will appreciate any suggestion to deal with this
Thanks
 

MisterBill2

Joined Jan 23, 2018
18,934
If the reading differ from the actual and the problem seems to be centered on the A/D converter IC, then there is either noise getting in or else the operation sequence of the conversion is being disrupted. For most A/D conversion schemes a stable and steady and noise free reference voltage is needed, AND the timing for each step of the conversion must be stable and correct.
So in describing the circuit and the operation please do not assume that the fault is in any small area an d choose to leave out information. THAT wastes time.
 

BobTPH

Joined Jun 5, 2013
9,124
I am going to guess the micro is using Vdd as its reference and the voltage supplying the micro is dropping when high current is being drawn. The lowered reference voltage would make all readings higher by the same ratio.
 

MisterBill2

Joined Jan 23, 2018
18,934
I agree with Bob. So I suggest that to verify that the problem is a drop in the reference voltage that using an isolated voltmeter of adequate resolution that you measure the reference voltage at the same points as the A/D system measures it, and verify the change. That may be a challenge if the A/D is a part of the micro package. In that case, measure the voltage at the power terminals of the micro using the isolated voltmeter. The change may be just a few millivolts, which is why I stated "with adequate resolution.
 
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