What is your input voltage? I think your inductor might be too small. Looking at the data sheet, they're using values of 170-220 uH. How did you "choose" that 10uH value?
(And I assume you meant you were using a 10uH inductor, not a 10uF...)
With your chosen CT=820pF…..that gives you ton = 20us and toff = 4us.
Generally you won't use all that on_time…you will hit the current sense reference of 300mV long before 20us….so basically, your buck is behaving as a constant off time buck converter with an off time of 4us….however, your fet may be off for more than 4us in any time interval due to the FB comparator…..so I also added a comparator feedback on the external voltage loop.
The attached is an LTspice simulation showing you how your buck works…you can sub in inductors and loads and see what you get….look at the peak inductor current….basically your peak inductor current will be 0.3V/0.235R = 1.27A
I have given you an effective current sense trip threshold of 300mv like in the MC33063.
To make it more accurate…you could implement BJT instead of FET, and get the relevant on state voltage.
LTspice is a free download from linear.com..now analog.com
BTW i assumed your load was 2.5W...but please change it if yours is different...what is your load by the way?
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to run the sim, change .txt for .asc...then open it in ltspice...then hit the running man icon.....then fill in how long you want the sim to run for, the start time, etc
What is your max load?
MC33063A is important to get exact part - also read the data sheet very carefully ...!
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View attachment 157675
here is the ckt from the data sheet - start with this I think ...
The most likely reason it works is the schematic has the wrong value marked on it. Probably just a typo but possibly to stop people copying it. If that is the reason, it worked!
Brian.
Do you have it working now?
Doesn't is have '100' marked on the inductor in the photograph. Most likely 100uH than 10 x 10^0.So they even mount a false board (with value wrong value) to take picture of it ?
if this is the case, I don't qualify this product as open source (as they claimed...)
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