For the maths, use the 'typical' values in the spec.
Let's assume R1 = 10kΩ, Vref = 2.5V, Iref = 1.5uA.
You want Vka = 23V.
So,
23V= 2.5V*(1 + 10kΩ/R2) + 1.5uA*10kΩ ≈ 2.5V*(1 + 10kΩ/R2),
23V/2.5V = 1+10kΩ/R2,
9.2-1 = 10kΩ/R2,
R2= 10kΩ/8.2 = 1.22kΩ
The values have helped me try and get my head around, the current in equation threw me off.
I misunderstood the datasheet and was using 10ma in the sum
Is 1.5uA fixed across the Vka range, otherwise it is harder to calculate?
The TMS102A combines building blocks of a dual operational amplifier, a dual comparator, and a precision voltage reference.
It is a very handy IC for adjusting voltage variations to fit the full input range of Arduino.
Seems to be good value for the functions.
What is your budget for achieving a reference voltage accurate to within even 0.01% or better? Do you have a temperature-controlled environment for the circuit?
A bit like the length of string question.
I looked for single or dual op-amp with high adjustable reference,
TMS102A is the only one I could find with high reference,
the others were set at 2.5, 2.6 or 5v.
If you stumble across another op-amp with reference IC of similar specs, let me know!
Always room for increased accuracy for the right price.
I like to look for bargains under $2 AUD per IC.
Cheers