Nice pointers scrat.
i hadn't considered decoupling the NI input of U1B, i'm going to add it as well, .01uF or 47nF should do it i think...
the R4 is on the schematic but not on the protoboard(in simulation i didn't notice any difference with or without R4, i should add it as well to the built circuit).
in my original circuit, C5 also wasn't there, i borrowed it from johnmx current sink circuit.
how would you do a differential config for the Rsense with x10/variable gain?, i've been looking at some circuits using opamps and i'd need to balance and match the 4 gain resistors and have to deal with the decreased impedance as well(unless using some specific differential amp like the INA106 that has fixed +10 gain, then again if i have to do gain adjust i'm screwed with that device).
Even without going differential, should the ground point being close/same as R10 do the trick?
Yeah i don't know why i'm getting such large difference with a straight soldered single-core wire, i'll redo the ground path to do single point ground today when i get home and add the missing R4 and the decoupling cap to ground.
BTW, forgot to add, tested the sink from 0 to 30V and the current didn't even blink, Vgate wasn't any different as well(i thought it would change, but i guess not).
i'm going to lower supply to +-12V as well, after all the only reason i'm using -rail is because the OPA4277 isn't RtR so U1B would never go to 0V.
I'm still seeing differences in set value to current measured even after setting the trimpot, but i can't be sure if it's because of the DMM inaccuracy in 10A range or those funky differences (side note: i need to get a good dmm, but no cash at hand atm).
Edit: After these issues it occurred to me:
1) Since the initial idea is to feed the output of U1B to the on-board ADC of a micro, thus having a direct current readout and i could calibrate via software, problem is that if the U1B output =! to the Vshuntx10(or to be more precise, straight Current across Rsense) i have no way of knowing what the "real" value is, as i'm using U1B as the sense amp as well which could lead me to over/undercompensate and have false data....
So... why don't i calibrate the sink in "best guess" scenario, without much precision issues and don't use U1B as sense?, then...
2) I use a low-side current sense like this one:
http://focus.ti.com/docs/prod/folders/print/ina220.html which as a bonus has I2C output, Vbus sense, etc etc and thus use that value as true feedback for the current sink(in software doing something like: rise Sink current by ".2 amps"(or whatever value) -> small delay -> read INA -> use difference as feedback, readjust), trick would be to do a feedback calculation that won't end in oscillation....
i don't know why i hadn't come up with that idea before... probably because i thought i wouldn't encounter these issues with the feedback amp being so imprecise