I fried my Nexus 7 topic

I was doing a car install of my Nexus because I wasn't really using it for anything else. I wanted a good power source so I could avoid the charging issues people were running to, so I went with a DC-DC converter instead of a cigarette lighter adapter. I used the same converter that many others have used, and dialed it in to the correct voltage output and wired it up to my USB-OTG Y cable. I plugged it into my tablet to test, and the system immediately shut down and got really, really hot. After I unplugged it and let it cool off, I was able to boot the tablet, but it no longer charged anymore from the wall socket adapter. I woke up to a dead tablet and started troubleshooting. I was tracing the power circuit and was seeing 5V everywhere except for at the battery connector. (Battery tested fine at 3.7V). After removing the metal shield inside the tablet I found this:
Needless to say, the thing is toast. I wish I knew what happened, but I don't. Everything appeared to be setup correctly. I'd like to blame the converter for being a POS, but maybe I did something wrong, who knows. Any one have any thoughts as to what could have happened?