A customer would like to know the details about a resistor divider used in both example circuits, so I will provide the schematics in question and my response in a REPLY post.
See the image below:
Thank you for your answer here, ARad - I've been struggling on another thread to get some help in an understanding of this?
If you don't mind some follow-on questions at the risk of appearing to be stupid?
By preloaded bias do you mean this voltage differential or some current differential?
Is it to do with the fact that min load current (to stay in regulation) for LT3083 is 1mA & for LT3081 is 5mA?
So for LT3083 acting as current booster to 3.3V would require R to gnd of 3.3K (for 1mA load) & hence 4.2ohm as the second R in the voltage divider to give 4mV drop - the datasheet shows X 10 of these values which reduces this load by 10 to 0.1mA so what gives???? There's also a differential between the R connecting the SET pin to load (20mohm) & OUT pin to load R (10mohm) but I doubt this comes into play?
For LT3081 as current booster for 3.3V, R to gnd of 660ohms (for 5mA load) & hence 800ohm for other resistor in voltage divider for 4mV drop - using X10 would give 6.6K (6.2K closest shown in the datasheet which only gives a load of 0.5mA - so again what gives?). here, there's NO differential between the R connecting the SET pin to load (20mohm) & OUT pin to load R (20mohm)
Are these calculation errors on my part ???
I updated the image in my previous post with some calculations.
Great, thanks, ARad
OK, then the LT3083 datasheet diagram stating a 4mV drop is wrong - it's actually 2.1mV drop?
The mV drop is not so consequential as it just turns off the output of the LT308X when a light load, I believe.
But the minimum load (5mA & 1mA) needed for regulation on these devices seems to be crucial to maintain regulation - unless when working in current mode they don't use regulation - in which case why wasn't the same voltage divider used on both LT308X devices?
My simpler calcs on R sizing for 1mA & 5mA gave me 1/10 the values used in the schematics - so I was/am thrown by these R values & the text in the datasheet schematics stating 4mV drop for both (when in fact it is 2.1mV on LT3083?) also confused/confuses me??
Just so I can be sure I understand -
- if I want to use LT3083 as current booster for regulated 5V, then a voltage divider of 50 & 33000 ohm will provide 5.1mV of bias between SET & OUT pins?
- I can ignore minimum load requirements?