I'm using AP65111A buck converter and it works fine. It has typical beginner-level ripples, somehow manages to keep the voltage under moderate load and so on.

However, following the schematic 1:1 for 3.3V output yielded literally no power output under load. Output capacitor is 22uF MLCC cap and input voltage is 6.5V (kind of non-negotiable factor in my use).

After I removed the capacitor C5, the converter started outputting power normally, but it gets massive voltage drop when 0.4A load is applied. It drops about 1.2-1.5V and doesn't recover even though feedback voltage is too low.

AP65111A typical application

My problems being:

  1. Why adding bootstrap capacitor causes converter to not output any power?
  2. The IC is rated for 1.5A continuous current but gets hot and cuts off at ~1.4W ([email protected]). Could it be fault of improper value of inductor or output capacitor?
  3. Could input voltage be a deciding factor here?


  • \$\begingroup\$ Hard to say without seeing the specs for capacitors and inductors and also the PCB layout. It should work worse when the capacitor is removed. \$\endgroup\$
    – Justme
    Dec 9, 2020 at 19:48
  • \$\begingroup\$ Could be a layout issue. Which inductor are you using? A link to the inductor datasheet would be helpful. \$\endgroup\$
    – John D
    Dec 9, 2020 at 23:00
  • \$\begingroup\$ Add a link to the data sheet. \$\endgroup\$
    – Andy aka
    Dec 10, 2020 at 11:19
  • \$\begingroup\$ Inductor: tme.eu/Document/a7bba15336bc08baa49ff14d85d5dea0/… IC: diodes.com/assets/Datasheets/AP65111A.pdf \$\endgroup\$
    – fotelpl
    Dec 10, 2020 at 12:42

1 Answer 1


Maybe try adding an external bootstrap diode from V_in (anode) to BST (cathode)? Could be schottky. That should get you up and running I would think.


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