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SITUATION

Hello All, I have designed a PCB the using a MT3608 to produce 5V from an 18650 Li-Ion battery. This is my second revision of the PCB (the first one worked fine), however this one has different behavior and the only the that changed was the component layout. This circuit is being used to power the following:

  • an ATMega328P (internal clock 8Mhz)-pulls about 12mA
  • A wireless transceiver (pulls about 15-16mA)

So my circuit draw about ~30mA total. this should be well within the current range of the MT3608.

PROBLEM

The circuit only outputs ~3.7-3.9V under load. If I remove the wireless transceiver it will then output 5V. Here's the peculiar part; If I use an external DC power supply and connect it to the output of the MT3608 and then raise the MT3608's output to 5V and then disconnected the external 5V source the circuit will happily maintain 5V until I cycle power.

Does anybody have any ideas?

Two things worth mentioning:

  • The first PCB (that worked well) had all empty space between traces fill with a ground plane.
  • The second PCB has it's capacitors located physically farther away from the MT3608

Link to MT3608 datasheet

360

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So I figured out the problem was due to the fact that the capacitor (C10) was located physically too far from the MT3608. Hopefully someone can learn from my mistake :)

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