Tool/software:
Hi everyone,
I have designed a custom Li-ion battery charger circuit using the BQ25306.
The charger initially worked perfectly, completing one full charge and discharge cycle without any issues. However, during the second attempt to charge the battery, it started charging normally but then stopped when the battery voltage reached approximately 3.3V. The initial battery (NCR18650B single cell) voltage was 2.7V.
Since then, the charger will not initiate a charge cycle. I have tried power cycling the unit and disconnecting/reconnecting the battery, but the problem persists:
- The STAT pin LED remains completely off. It does not indicate charging (solid on), charge complete (off after charge), or any fault condition (no blinking).
- Upon probing the IC pins, I discovered that the REGN pin voltage is only 0.36V. According to the datasheet, this pin should output approximately 5V to supply the low-side FET driver.
- I have the required 2.2µF ceramic capacitor correctly placed between the REGN pin and GND, close to the IC.
- On an identical, functional board, I measure the expected ~5V on the REGN pin.
- The main input voltage (VIN) is stable and within the correct operating range (12V). The battery voltage was around 3.3V when the charging stopped.
This low REGN voltage seems to be the likely reason the IC is not functioning. Could this indicate an internal failure of the BQ25306's internal LDO? What could cause the REGN voltage to drop to 0.36V after working initially? Are there any other potential causes or troubleshooting steps I should consider before concluding the IC is damaged? I have visually inspected the board for shorts or damage around the IC and found nothing obvious.
Any insights or suggestions would be greatly appreciated.
Thank you,
