I'm pretty new at hardware side of things and trying to teach myself circuit and PCB design just as a hobby, so. bear with me if I'm annoyingly noob for you.

As a relatively simple first task, I decided to design a USB powered Li-Po charging - 3V3 LDO circuit. It looks like a pretty common hot-plug type design. basically when the USB cable is connected it cuts the Li-Po from the load and charges the LI-PO while powering the circuit from USB power. When USB isn't connected it uses LI-PO power. Here's how it looks:

enter image description here

The problem(?) is with the Schottky diode (D5) which is supposed to block the current from Li-Po to USB (and the MOSFET gate) when the USB cable isn't connected.

I used the following diode for my prototype: https://datasheet.lcsc.com/lcsc/2303141100_MDD-Microdiode-Electronics--SS54_C22452.pdf

Anyway, after getting 5 prototype boards I noticed: When I unplug my USB and plug in a LI-PO Battery (when the Li-Po is at around 4 V) I see 2.55 V at the Schottky's anode terminal. Now I know you're supposed to have reverse leakage with a Schottky diode and it can be high. The unit functions correctly, but that 2.55 V is giving me an itch. Is this normal for this diode? At first I thought the diode may be faulty but all 5 prototypes consistently have the same voltage at that terminal with that 4 V Li-Po.

If this is normal, is this a problem in general? (let's say I will power a MCU board with this)

I'm not sure if it's relevant, but the input impedance of the multi-meter I use is 1 MΩ.

  • \$\begingroup\$ Are you sure it's only the Schottky diode leaking? You have other components such as the charger IC between 5V node and battery voltage too. \$\endgroup\$
    – Justme
    Dec 1, 2023 at 9:51

1 Answer 1


Look at Fig.2 in the Diode's Datasheet (Typical reverse Characteristics). 25µA reverse leakage are exactly in spec for the Diode.


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