The AD586 (5V reference) has a trim pin on it. I would like to use that trim pin to crank the reference output up to 5.12V. Unfortunately, there is no equation to help me select the proper resistors needed to do this. Figure1 of the datasheet shows resistors, but doesn't give values. Are these resistor values known, or are they trimmed at the time of manufacturing? If they are known, I could use those to come up with my own equation.
Is it possible to get either the equation or the resistor values? If necessary, approximating will do fine, just need an initial guess for the trim resistors.
The references are supported out of San Jose, CA, so we had to go back to corporate and have them access the archives
for this 1987 vintage part. The .pdf that they sent is a little hard to read, but it looks like ~6k for the feedback RF, ~14k to
ground (RI), and ~125k for the trim resistor, RT. Both RF and RI are shown as trim resistors, so depending on whether the
Zener is a little high or a little low, or the intial RF and RI are high are low, RF or RI is trimmed. My guess would be no
more than 10%.
Although I can uderstand why you would want 5.12 Volts (512 = 2^9) nowdays with microprocessors, people use 5.00V
(lots of choices) and do scaling in software. My personal favorite 5V reference is the ADR435 because it is one of the
few references that allows you to easily overcompensate the loop and get rid of noise peaking. See "High Frequency Noise"
starting on page 16 of the datasheet: