In the datasheet the data are specified for a 600 Ohms resistor, can it be that the low resistance is giving you bad results?
Thanks for the answer,
No I just mentioned the 2 resistance values. I measured with E12 from 100 to 100k, knowing that on the high end the voltage over the resistance will become too high.
See attached picture -
X-Axis=resistance 100-120-150...82k-100k (logaritmic scale)
D1a=Source; deviation in % from 31.875uA
D1b= Source; deviation in % from 32uA
D2a=Sink; deviation in % from 31.875uA
D2b= Sink; deviation in % from 32uA
It looks like D1a and D2a goes to 0.4% at origin (255/256=0.4% !!!)
It looks like D1b and D2b goed to 0% at origin
For calculating these values, I measured the resistance of the resistors used also with the HP precision meter.
dev.png 27.4 K
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If you do an error budget analysis the results you are seeing well
within spec -
The voltage ref specs are -
So you could use a precision R, the DelSig A/D, and possibly have a built in self cal
correction to improve the overall specs for the IDAC. However you are intrinsically
limited to 8 bits, ~ +/- .4%, so not sure even this approach would be useful.
You could use PWM, OpAmp, Bipolar PNP and develop a more accurate I source,
but this would require a precision ref driving Vdd.
Thanks for answering.
I know it is within the range of the datasheet. I am just trying to get a current source which is as accurate as possible. The 32uA / 0.1% which I have now suits me very well. When using the IDAC on less then Full Scale, the output gets more inaccurate (but still within datasheet mentoined limits)
While working on my first PSOC project, I am positively surprised every day about the possibilities of these devices (PSOC3/5LP) and the flexibility and accuracy I can get. :-)