I examined my MP1584 module and learned it was activating at far too low of a voltage. I want this buck converter to deliver 3.3V, and generally buck converters need input voltage a few volts (~2V) above the specified output. By that rule of thumb, my project shouldn’t activate until somewhere north of 5V, but it was activating at 3V and making a sound I could hear as it tried to perform an impossible task. This can’t be good.
I thought I would try modifying the board with different resistor values to raise its input enable voltage level. I will leave the low side resistor as-is at 100kΩ between EN and GND, and replace the high-side resistor. Looking through my commodity resistor pack, I thought a 220kΩ in series with 470kΩ should do the trick. Having 690kΩ between Vin and EN, and 100kΩ between EN and GND, should result in a voltage divider that activates EN (1.5V) when input voltage rises to approximately 11.85V.
At first, I thought I would have to switch to my small soldering iron tip to remove the existing high side resistor. But before I switched, I noticed my normal soldering tip is almost the same width as the resistor, allowing me to heat up both sides at the same time for removal. It left a big glop of solder doing so, but that wasn’t too hard to clean up. I then soldered the two resistors, in series, between the EN pad and Vin pad. Since these are through-hole resistors and not surface mount, it was not elegant. But it seems to work.
Slowly increasing input voltage with my bench power supply, I didn’t hear unhappy sounds at 3-5V. Nothing happened until I was close to 12V, at which point the MP1584 came alive and started delivering 3.3V. Success! Or so I had thought… and proven wrong by a puff of smoke.