I assembled a 12-to-5V buck converter from an LM64460-Q1 (
datasheet) and I'm not getting any output. Schematics and board layout are attached. Here was my process and observations for testing the board:
* I slowly ramped the input voltage up with no load connected and noticed no current draw until 4V at which ~50mA started to flow. At around 6 or 7V the current spiked to 1A for a few seconds and then dropped to 6mA when I reached 12V. At this point I checked the output voltage which was only ~1.2V but was very slowly rising.
* I removed supply to Vin, briefly shorted the output terminals just to discharge the output caps, and reconnected 12V input. Now I have 0V output and that's all she wrote.
I checked all the other pins and other than the Vin1 and Vin2 pins and EN, all are 0V (including VCC which is nominally a 3.3V LDO output). I desoldered the chip and found the SW1, SW2, and SW3 pins shorted to GND, so the chip seems cooked. I guess I should have pulled the plug before I got to 1A draw.
Before I solder a new chip, is there something wrong with my design that one would expect to fail like this?
Before powering I did check for shorts but I'm not sure how to test for unconnected pins... doesn't seem likely that an unconnected pin would cause failure like this however.