Battery protection low voltage disconnect issue

[SolarTrap]

Hello all,

just got my first EasyEDA project back from JCLPCB and it’s almost as I envisioned it.
My issue is the under voltage protection. It correctly disconnects the battery but I can still measure 0.7V between Vcc and GND.

My question: how to track down this issue?

I have attached the full circuit, the bottom part is the charger which was a public circuit I just integrated. It seems to be a standard implementation of the parts.

Thanks in advance,
Markus

https://files.engineering.com/getfi...3&file=Screen_Shot_2022-04-28_at_16.42.56.png

 

[Clash3]

Try blocking the light hitting the LED's, I suspect the LED's are generating a small voltage that you are seeing.

 

[itsmoked]

I'm with Clash3. Check again in darkness.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SolarTrap]

I ran the darkness experiment and it has no impact. I do not even understand why it would matter as the battery monitor disconnects GND from Battery Minus (via the FS8205A component).

 

[3DDave]

Lift the pins that tie FS8205A to ground and see if the voltage changes. Alternative, cut the trace(s) to those pins.

 

[itsmoked]

0.7V is suspiciously a Si diode voltage.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SolarTrap]

So i removed the FS8205A and I still measure 0.7V
what I can measure now is a is -0.2V (when the battery is completely removed) coming from the 25x WS2812 LEDs when they are exposed to light.

 

[3DDave]

So that leaves U4, which sits between the battery and ground.

 

[SolarTrap]

This means I remove R8 as a test?

 

[3DDave]

Seems reasonable. That's the problem with unexpected conduction - keep removing items until the conduction goes away on the paths that seem most likely first. Same thing with mystery short circuits in car wiring.

 

[SolarTrap]

So I removed R8 and now i read 0V !!
Is the circuit wrong? I have attached the 'typical application' diagram from the specs.

https://files.engineering.com/getfi...d&file=Screen_Shot_2022-05-01_at_16.41.40.png

 

[3DDave]

The circuit may be entirely correct but the components selected might have a problem - do you have a link to the data sheet of the U4 component?

 

[SolarTrap]

Yes DW01, attached:

https://files.engineering.com/getfi...-e0e5-44dd-8caa-3a728b71c4c5&file=DW01A-G.pdf

 

[SolarTrap]

To solve the puzzle: attached is the fixed circuit.
In- and output to the mosfet module was swapped

 

[3DDave]

Well - that would do it. Thanks for the update.