Hi.
I plan to use 4x DDC112 devices on a PCB to provide 8x channel current measurement. I need to extend the measurement range by adding external integration capacitors.
I am following the datasheet guidelines for choosing the capacitors. Page 10 says..
Since the range accuracy depends on the characteristics of
the integration capacitor, they must be carefully selected. An
external integration capacitor should have low-voltage coefficient,
temperature coefficient, memory, and leakage current.
The optimum selection depends on the requirements of
the specific application. Suitable types include chip-on-glass
(COG) ceramic, polycarbonate, polystyrene, and silver mica.
So I am looking at using C0G 0805 type capacitors. https://www.digikey.com/products/en?keywords=GRM1885C1H221FA01D
Tolerance = +/-1%;
Temp Co = +/-30ppm (not big problem will be used in air conditioned environment)
10Gohm insulation resistance
My question is related to the capacitance tolerance of +/-1%. Does the DDC112 do some sort of a internal correction during the m/r/az cycle or at some other point in time? See page 13 DDC datasheet (It is active whenever a measurement/reset/auto-zero (m/r/az) cycle is in progress) What is the auto zero?
I doubt that this is done or even possible. I assume I will have to correct for the capacitance tolerance in my implementation. I can't see how one would do it without injecting a very accurate current source into each input during a initial calibration phase to estimate the values of the external integrating capacitors. The 13pC test input's accuracy is +/-10% in the datasheet. Not very helpful.
Any ideas and thoughts are welcomed.
Chris
