This is a circuit to measure a current flow that is 0-10A DC. The output goes to an ADC.
The circuit itself works fine, however, over a dozen cards, the output of this circuit is all over the place.
At rest, I=0, the output offset can vary by a factor 10 (300 to 3'000 count on the ADC) from one board to another; but is stable in a specific board.
So far, it might be related to the input offset voltage, given at 0.11mV typ. but this would account for perhaps 10%.
The manufacturing of the cards was also poor and noticed some pads seem not well soldered, I wonder if that could be a cause as well.
Are there other fundamental flaws in this circuit?
I need to fix an existing batch of boards.
- VDD: 3.3V
- ADC is 0-3V with 0.1% reference. the ADC is not saturating.
- ADC is 12bits, 16 measurements summed: 16*12bits = 65535 counts.
Two random cards measured at rest I = 0A voltage at the circuit output:
- A: 150mV / 3445 count
- B: 34mV / 336 count