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Hello everyone!

I am trying to test this circuit, but actually I have some issues with LDO power supply!

Actually the problem is that, the two LDO: LDO_circuit and DLDO are working fine. I mean that if the power supply is 3.3 V they put on output 2.6 V and if the power supply is 5 V on the LDOs'output there is 3.3 V. Instead, on LDO_uC I have always on output very few mV even if I checked that on input I have the given power supply. Someone have ideas to suggest?

Thank you very much in advance!

  • \$\begingroup\$ Have you checked the output for a short circuit? It could be solder, a bad capacitor or any number of things; I might be suspicious of a short at pins 17 and 18 of the controller - Vcc and Gnd respectively aalthough it looks like theey are corner pins. \$\endgroup\$ Commented Feb 21, 2016 at 17:02
  • \$\begingroup\$ You appear to be saying that the problem is things are working fine. I'm confused. \$\endgroup\$
    – Andy aka
    Commented Feb 21, 2016 at 17:13

1 Answer 1


Looking at your schematic you have pin 1 of the uC (GND) connected pin 32 (AVCC). You have created a short between GND and the output of the LDO via the 2 inductors (or ferrite beads).

It is simple to prove this: remove "Inductor uC" from the circuit, and the output of the "LDO uC" should be 3.3V.

The solution is probably to lift (disconnect) pin 1 of the uC and use some fine wire (mod wire) to connect it to GND somewhere else.

It would make it easier to refer to the parts on your circuit if you used a standard way. Rather than calling the LDO's "LDO 3.3 circuit" it would be better to call them U1, U2, U3 etc. Inductors are always called L1, L2. Ferrite beads can be FB1, FB2. Capacitors are C1, C2, etc. Connectors are usually K1, K2.

  • \$\begingroup\$ Thank you very much for all your answers! Indeed there is both a short circuit between pin 1 and 32 and 17 and 18. If I remove Inductor_uC, do you think I can solve both these problems? \$\endgroup\$
    – Francesca
    Commented Feb 23, 2016 at 9:30
  • \$\begingroup\$ @Francesca Removing the inductor does not solve the problem, it just allows you to verify that the LDO is working correctly and that the fault is elsewhere. One of the basic methods of fault finding is to disconnect parts of your circuit so you can test them in isolation. You will need to lift up pin 1 of the uC and connect it to GND somewhere else (eg pin 18). \$\endgroup\$
    – Steve G
    Commented Feb 23, 2016 at 9:59
  • \$\begingroup\$ Actually I solved the problem: pin 1 uC is now connected with a wire to a GND directly. It was the shortest correction I could do. Hopefully will work. Thank you again! In reality I tested again and the short circuit between 17 and 18 is not present. Now it seems to work fine:) I will try to test the board. Thank you again for your consuideration! \$\endgroup\$
    – Francesca
    Commented Feb 23, 2016 at 11:06

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