I’m hoping someone here can set me on the right track to fix a schematic that went wrong somewhere.
I made a power supply sub-system (image below) for my PCB about a month ago. My project is powered by a 3.6V 13Ah LiSOCl2 battery. Battery-VIN is connected to D1. The purpose of this power supply system is to ensure that I would always have a steady 3.6V output even during high current draws (up to 800mA) and cold-weather conditions (down to -20C). Previous tests without this power supply system showed that under these conditions the battery-voltage could drop as low as 2.8V which would create frequent brownouts on my microcontroller (Particle Electron).
I based my schematic + parts on this datasheet (page 1).
Note that since VIN is 2.8-3.6V, and VOUT should be 3.6V, I went with the 610995 model with FB connected to GND. W1+W2 are two wires with a JST-PH2 connector that can be inserted into my microcontroller to power it.
My DRC clearance is set to 6mils, and object clearance is set to 10mils (as per manufacturer’s recommendation).
Yesterday, I finally received this PCB (10 copies). I tested it and while it worked for 3 copies, for the remaining 7 copies some parts (particularly U1 and L1) became extremely hot to the touch and VOUT was 0. Clearly, something went terribly wrong. I looked at my parts again, and here’s my thoughts:
(1) The maximum rating for D1 is 500mA, which is too little for my project. Nonetheless, just by powering up my PCB these components should draw nowhere near that amount.
(2) The saturation current for L1 is 1A, which ideally should be higher. But again, simply powering up my PCB should draw nowhere near that amount.
(3) C1+C2 = 20uF, but the maximum here can be 100uF. To better mitigate current drops, stronger capacitors should be used.
Basically, after seeing that my PCBs didn’t work, I looked into the parts and came up with several things that can be improved, but nothing so far that could explain why my system entirely didn’t work.
I’m really hoping someone here can give me a push in the right direction as I’m not sure what else to look at.