I'm trying to use TI's LMR16006 Simple Switcher Buck Converter to regulate 48V down to 5V on my circuit.
I used TI's WebBench tool to calculate component values for their reference design, and had a board fabricated according to the design:
I hand-soldered a prototype of the board, and was able to get it working after some finicky hand-soldering. I had some trouble, but assumed that it was just due to poorly soldered joints (since I was hand-soldering a bunch of small parts for the prototype).
Then I had 10 boards professionally made, and I'm finding that they don't function at all. V_out (across C6) is 1.26 V, and I'm expecting to see 5V!
I checked a couple of obvious things on the nonfunctioning boards:
- I checked connectivity across the board to see if there were any bad joints and/or if anything was wired incorrectly, but that doesn't seem to be the issue.
- The bootstrap capacitor (C4) needs to have a voltage of at least 3V; in both of my boards (working and not working), the voltage is around 6-7 volts.
- I was concerned that perhaps the SHDN pin was being pulled low, but on both boards the value is hovering around 5V, which should be high enough to ensure that the regulator itself isn't shut down.
After looking at them on scope, it looks like the on the working board, the SW pin is switching at the correct frequency (~700 kHz), while on the non-working board, the frequency is MUCH slower (~150 kHz).
I'm trying to figure out why the converter's not working as expected, but I'm honestly not sure what to investigate next. Any suggestions for how to proceed troubleshooting would be super helpful.