We received a set of prototype boards. They have a DC power supply input feeding into a step-down converter, which is built around an RT6224D. It is supposed to deliver 5.0V. The circuit is almost exactly straight from the datasheet, just that the designer chose a 3.3 uH inductivity.
The problem is, I get exactly 0V at the output. And I can not figure out why. Even on a quick breadboard reproduction of the same circuit, I still get 0 output. I have this feeling there must be something very obvious.
Do you have any idea what is going on here? I greatly appreciate your help!
Edit to answer SamGibson's questions:
(c) Someone else did the design and the layout, I am just trying to make it work. The boards came from a domestic manufacturer. I talked with the designer about the issue, he said U6 it must be a faulty chip. On all 5 boards. So I replaced it with a new one, same result.
(d) I don't know where the board manufacturer got the components initially, my replacement was from Digikey.
(e) I can't find any usable signal to scope, VIN and EN are at 12V, all other pins show a flat lines at 0V.
(f) The inductor is an ASPI-4030S-3R3M-T.
This is my "hotfix" based on the feedback by Randy Nuss and Spehro Pefhany. The originial RT6224D did not work any more, but with a new chip and the 100k resistor, I get the desired 12V: