Hello,
I am designing a handled device powered by a 1S LiPo battery. We use the MP2760GVT-010A to manage the battery charging from a 4.8V input.
Our design is in production at the moment but we discovered a severe issue with charging a dead battery. Previously, we made these tests:
- Apply 4.8V at charger input with no battery ==> VSYS is powered and stable
- Apply 4.8V at charger input with dead battery ==> VSYS is powered and stable
However, we recently discovered it is not always working. We tested it on several devices, some from production, some from engineering samples, some assembled in house, and the verdict is the same. It might work or not. Sometimes it does not work, sometimes it does not work until we remove the 4.8V input, sometimes it works if we plug the battery after the 4.8V input. All cases observed on each device.
This happends:
- with and without load on VSYS
- with and without host I2C communication.
Unfortunately I cannot upload pictures (Schematic, oscillo view, …) but I’ll try to explain.
Checking with an oscillo, we the charger is cycling the power-up sequence, with around 400ms period.
VSYS has kind of a saw teeth profile, reaching the target VSYS then directly falling down.
Zooming on VSYS where it reaches its target value, we see that BGATE is activated to start the charging process. However, it never reaches its rated 6V, quickly drops to less than 1V then turns back off. This means the BAT MOSFET is never activated (we could observe no movement on VBAT).
Furthermore, INT is never pulled low and ACOK is aloways low. However, I am not sure about the error reporting on the INT pin as it is disabled by default and the MCU maybe has not the time to enable it.
So my question is, what could cause such behavior?
Otherwise, the system runs perfectly fine in all other situation. We have tens of devices in test on field for more that 2 months now and there is no issue in nominal conditions. The problem only appears when battery is fully depleted.
Thanks in advance four your insights.