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Variable output buck problem in regulation( or lack of it)
QDrives , 07-29-2024, 09:08 PM
What is "mess xcel"?
Sniper2 , 07-29-2024, 09:08 PM
that 0.9-1V is still there for some reason , if it was the FB voltage then yea i vould understand somehow but it is that + something
Sniper2 , 07-29-2024, 09:08 PM
mesured - expected , or rather error
Sniper2 , 07-29-2024, 09:09 PM
the offset i wanted to also plot it since i think it can help
QDrives , 07-29-2024, 09:10 PM
So what do you measure with DAC output voltage 0V, 1V and 2.5V?
QDrives , 07-29-2024, 09:11 PM
My calculations still seem different compared to yours.
Sniper2 , 07-29-2024, 09:11 PM
maybe it is FB_v + what is droped over the DAC resistor? then again it is likesuper low current
Sniper2 , 07-29-2024, 09:13 PM
0V expected 4.56V measured 5.46
1V 3.59 measured 4.502V
2.5 2.148V measured 3.132V
Sniper2 , 07-29-2024, 09:14 PM
uploading to git xcel that i have atm
Sniper2 , 07-29-2024, 09:14 PM
here too in case u dont want to use git
QDrives , 07-29-2024, 09:15 PM
My calculations:
0V --> 5.36V
1V --> 4.36V
2.5V --> 2.86V
Sniper2 , 07-29-2024, 09:17 PM
hmm much closer but at the end it still drifts a lot
Sniper2 , 07-29-2024, 09:18 PM
ill restudi your math and see , the next evening
Sniper2 , 07-29-2024, 09:18 PM
good night*
QDrives , 07-29-2024, 09:18 PM
Could be average compared to peak of the ripple...
Good night.
Sniper2 , 07-30-2024, 02:00 PM
I can also average out like 10 100 samples
Sniper2 , 07-30-2024, 02:01 PM
Should be able to from the chip itself but I'll do it in code
QDrives , 07-30-2024, 08:20 PM
What about tolerances?
Sniper2 , 07-30-2024, 08:55 PM
standard JLC so 1% if i remember well
Sniper2 , 07-30-2024, 08:56 PM
i measured them and thy all seem to be very close to mnominal and all are a bit lower resistance so ratios are not massively changed
Sniper2 , 07-30-2024, 08:56 PM
PS did not have time to test new code or eamine your xcel due to IRL problems
Sniper2 , 07-31-2024, 07:54 PM
didnt make it in time ill return to this project in like 10-11days from now
Sniper2 , 08-02-2024, 07:29 PM
Hmm so you computed current and based on that vout
QDrives , 08-02-2024, 09:34 PM
Yes.
Sniper2 , 08-10-2024, 05:52 PM
ok i am back and redoing the math + some corrections for reference and leakage ....
Sniper2 , 08-12-2024, 07:45 PM
now it seems to work way better in terms of math
Sniper2 , 08-12-2024, 07:50 PM
at this point i think i am into tolerances and i have no idea what is the FB input current well it is pA or less BUT my current is like 0.8uA in that node
Sniper2 , 08-12-2024, 07:50 PM
then again i wander why my initial math screwed up ... maybe forgot a current direction and fb voltage at some point
QDrives , 08-12-2024, 09:17 PM
You might want to do a tolerance calculation.
If you are still outside the tolerance, then we are missing something else.
Sniper2 , 08-14-2024, 06:17 AM
It seems out of my rought math that I am in them more or less
Sniper2 , 08-14-2024, 06:18 AM
Fb input current in not documented and I did not account for fb voltage tolerance so I am sort of sure in tolerances
Sniper2 , 08-14-2024, 06:31 PM
so:
deviation from expectd is from 1.8% to 7% + 2 odd cases of 14% but that is proably typo on my part since there was no change
Sniper2 , 08-14-2024, 06:34 PM
my resistors are 1%+- AND Vfb is itself 1% +- and on top of that there is that unknown FB current needed by the IC itself
Sniper2 , 08-14-2024, 06:35 PM
and i forgot to mention that i bodged a THT for the DAC resistor and that is 5% or worse....
Sniper2 , 08-14-2024, 06:37 PM
5%
Sniper2 , 08-14-2024, 06:38 PM
ill correct the c++ code and then add code to compute on the fly deviation and % deviation
QDrives , 08-14-2024, 07:54 PM
And your DAC output is correct too?
Sniper2 , 08-14-2024, 08:06 PM
like measured?
Sniper2 , 08-14-2024, 08:07 PM
i am makeing a function for averaging readings
QDrives , 08-15-2024, 07:39 PM
Yes, did you also measure the DAC output.
Sniper2 , 08-16-2024, 04:13 AM
No, that needs to be done by hand .
The % error code is running but buggy atm since vout is wrong typo somewhere
Sniper2 , 08-16-2024, 07:09 PM
ok so new data is is basically this:
at the scale extreme error is large like 10% while in the middle it is like 1%
Sniper2 , 08-16-2024, 08:02 PM
corected code
Sniper2 , 08-16-2024, 08:03 PM
now it is way more precise and typeinf new data
Sniper2 , 08-16-2024, 08:03 PM
BUT now it is like a 0.1-0.2 V offset
Sniper2 , 08-16-2024, 08:30 PM
-6% max error
Sniper2 , 08-16-2024, 08:30 PM
error seems to grow liniarly so i think it is current related from seomething
Sniper2 , 08-16-2024, 08:31 PM
BUT good enough for now ....
ill akso need to math out the reverse fucntion + code to rectly read current
Sniper2 , 08-16-2024, 08:31 PM
@QDrives
QDrives , 08-16-2024, 11:28 PM
I would redo multiple measurements at random just to see if it is a measurement / documentation error.
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