BQ25628E: Issues with Charging and Calibration Using BQ25628 and BQ27Z746

Gopika Raj V S

Part Number: BQ25628E
Other Parts Discussed in Thread: BQ27Z746

Tool/software:

Hi Team,

We are currently using the charger IC BQ25628ERYKR in conjunction with the fuel gauge BQ27Z746YAHR for charging and monitoring a 3.7V, 1500mAh LiPo battery in our new design. However, we are encountering a couple of issues:

Charging Issue:
- We are unable to charge the battery through the fuel gauge. We’ve observed an unstable output at the SYS pin of the charger IC. Despite providing a stable 5V input, the output voltage at SYS as well as the BAT voltage of the charger IC fluctuates between 2.7V and 4.2V.
- Could you please help us understand why this instability is occurring and how we might resolve it?
Calibration of the Fuel Gauge:
- In our attempts to calibrate the fuel gauge, we have discovered that a constant current source is necessary for current calibration. Could you please explain what a constant current source is and how it can be implemented in our design?

For your reference, I am attaching images showing the varying voltages along with the charger IC input.

over 1 year ago

0 Michael Emanuel35 over 1 year ago

TI__Mastermind 40305 points

Hello,

Please provide all the register settings and schematic for when you cannot charge. It seems at first glance the gauge is not being activated, and the charger is charging the small output cap instead of the battery because the FETs for the gauge are not being connected. Please capture the above waveform to see 2-3 cycles so I can confirm.

Regards,

Mike Emanuel

0 Gopika Raj V S over 1 year ago in reply to Michael Emanuel35

Intellectual 360 points

Hi,

I am hereby attaching the schematics, the corresponding GG file. Please note that waveforms can be shared shortly. Kindly review them and let me know your feedback.

ZCS_SCH_REVA_30MAY2024.pdf

board3_27aug2024.gg.gg.csv

0 Michael Emanuel35 over 1 year ago in reply to Gopika Raj V S

TI__Mastermind 40305 points

Hello,

The schematic seems ok from what I can tell on the charger side. Please provide all the register settings and values when this is happening.

I will let the gauge team comment on the gauge schematic.

Regards,

Mike Emanuel

0 Jonny over 1 year ago in reply to Michael Emanuel35

TI__Mastermind 24741 points

Hello,

I do not see any obvious issues with your schematic for the battery fuel gauge. For the calibration process, please refer to the BQ27z746 EVM user's guide. I understand that you are not using the EVM and are using a custom board, but the principle should be the same.

Regards,

Robert.

Power management

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BQ25628E: Issues with Charging and Calibration Using BQ25628 and BQ27Z746