LiPo charger with load sharing

Question

I'm trying to make a LiPo charger + load sharing module that is mostly based on the popular TP4056 charger modules, this is my schematic:

I've made the prototype and the charging and protection part seems to work fine, but when I disconnect the power source (IN+ and IN-) and the module supplies the power from the battery, there is some leakage(?) somewhere and I can measure a voltage difference on the IN+ and IN- (around 1.17V). I thought the D3 diode was supposed to prevent this.

Am I missing something, is there something wrong with my design? How can I prevent this 1.17V to appear on the IN side?

PS: "VB" and "CH" are there to allow measuring with a microcontroller, but even if I remove those I experience the same.

Answer 1

Schottky diodes give you a low forward voltage drop but at the expense of higher reverse leakage. Looking at the manufacturer's datasheet, you can see the value at 5 V is typically a little over 10 uA:

12 uA flowing through R5 and R6 would give a voltage of about 1.13 V between IN+ and IN-

There may also be a small leakage through U1 to contribute to that.

In practice, leakage values as low as that are probably not going to cause you a problem; 12 uA of leakage will take over 9 years to discharge a 1 Ah battery, much longer than the battery's self-discharge rate.