I created my first buck converter circuit and I keep frying the buck IC. I created the design in TI webench, copied the schematic over to KiCad and then designed my pcb. The goal behind this was to be able to have JLCPCB assemble the boards for me. Normally I assemble my own boards, but due to amount these will be sold for, ie not much, I want as little as my own time in them as possible.
So what is this? This is a power distribution block for 12V DC and 3x USB A connector for 5V usb devices. The idea is to plug the input into a 12V DC power supply, then you have 4 pair of 4mm connectors to power your chargers and other items for RC racing. A lot of racers complain that the cheap USB connectors they get don't supply enough current so I wanted to design my USB 5V with a buck converter that could supply high current.
The webench design parameter was 8A and 5V, and it conveniently spits out a circuit for me. I then went through BOMs of the designs and chose one that JLC had the components in stock for, with the exception of the inductors. This was really the only change I made from the webench design. I chose a 2.2µH inductor instead of the 3.3µH in the design, however I did look at the datasheet of the TPS51396ARJER and it suggests a 2.2µH inductor for use.
Long story short, the completed boards that JLCPCB sent me short the VIN as soon as power is applied. No load being applied through the USB connectors, it shorts on power up. The IC burns up with a little flame, and melts the solder mask above the traces (yes the IC is placed correctly). When I remove the component the short is gone. So there is not a short in the traces. This happened with all 5 prototype boards I got from JLC. Kind of expensive failure since this was done in 2oz copper and ENIG finish.
I am attaching the webench design, my schematic, my pcb layout and the BOM.
I hope this is some minor mistake I missed that can be easily fixed, thanks for any help.
-Andrew