MP2625B puts only 1V in BATT (pad 14) if there is no cell when VBUS is plugged to IN (pad 1)

Battery Management
1

Hi, we received our first prototypes of our phone PCBs and we are having an unexpected issue with the charger IC.
The IC we are using is the MP2625B. We are using single LiPo pouch cell. The cell has its own typical protection for undervoltage (it opens a high side mosfet when discharges below 3V).
CC in the IC is setup at around 900mA.
The input to the charger is VBUS (5V).
(1) If when I plug VBUS to 5V, the cell is disconnected, the chip will put around around 1V in BATT pad (this is unexpected, I was expecting CV voltage 4.2V in this case).
(2) If when I plug VBUS to 5V, the cell is connected, it will enter in CC and I’ll see battery voltage in BATT pad. If then I unplug the cell, I’ll get CV voltage in the BATT pad as expected.

The issue is that (1) is very normal for our product usage, as when the battery discharges, the cell protection will open the cell mosfet. When the user plugs the phone to USB, the charger IC should output 4.2V to reestablish cell and start charging.

Currently with this behaviour, the cell will keep the MOSFET open and won’t charge.

I need urgent help, as I have been trying to solve it for the whole week, I couldn’t and need to give a solution to the CEM for fixing it.

Thanks!!! Best.

MP2625B
MP2625B1756×981 315 KB

wrong in the setup of the chip

2

To add info:
In this state where the charger IC outputs 1V in BATT (pad 14):
VCC (pad 20) is 4.5V solid
CHGOK and ACOK are both in 0V solid

3

To add more info:
I didn’t setup VSYS_FB (left it floating). So VSYS is regulating at 3.6V.

In a nutshell: What do I need to do in order to have, with No Battery connected, 4.2V in the VBAT node?
Is the problem that I left VSYS_FB floating?

This is the waveform that I’m currently having in VBATT. Also attaching the plot that I want to achieve (taken from datasheet… I guess “R6 and R7 floating” is incorrect?

vbat_error
vbat_error1478×287 16.5 KB

vbat
vbat935×777 197 KB

4

I did the rework to use VSYS_FB, and regulate the DCDC at 4.2V. But same, if I start the charger with cell with open MOSFET, the charger puts only 1V in BATT pad. How do I suppose to wake up a battery that triggered UV protection?

Please I need your advice, I’m getting quite desperate :-\ .

5

Hello Sebastian,

Given the urgency and complexity of the situation, I have notified local support to give you more direct support.