I have been puzzling over this for days now, and cannot for the life of me figure it out...
I have a constant current source set up to use as an analog dimmer for my LM3429 LED driver. I have made very slight changes in order to use a digital potentiometer and avoid issues that arise from bad tolerancing of that part.
Here is a stripped back version of the cicruit I am testing on.
What I have observed so far:
- When unconnected the LM4120 reference give a stable 5V.
- The potentiometer is definitely changing
- When top of potentiometer is connected to reference, Reference drops to 3.9V
I really have no idea what is going on here. Can anyone help me debug this?
LM4120 DS: http://www.ti.com/lit/ds/symlink/lm4120.pdf
LM3429 DS (page 14): http://www.ti.com/lit/ds/symlink/lm3429.pdf