BQ25306: Issue on output side when battery is not attached

Zhonghui Xu

Part Number: BQ25306
Other Parts Discussed in Thread: BQ25302,

Hi team,

1.I have noticed strange thing when battery is not connected with IC. Both battery and load is not connected --> Measured voltage across SW pins (inductor included) is ~4.15 Battery is not connected and Load is connected --> Measured voltage across SW pins (inductor included) is ~1.5 and not getting enough power to drive the load. The question is, how can i drive the load independent on presents of battery when VBUS is available?

2.i have additional enquiry on same part. i connected battery in reverse polarity, then it got short circuited and melted positive terminal from battery.. but circuit is fine.. But i don't understand how it got shorted . and what is the path for return current

Thank you very much for your help.

Best regards,

over 3 years ago

0 Kedar Manishankar over 3 years ago

TI__Mastermind 24075 points

Hi,

This is a non powerpath device and you will not be able to drive a CC load on its own at the output. You would need to consider the topology with SYS load hanging off of PMID, or a battery always present configuration with SYS load hanging off of the battery. With regards to battery reverse plug in, the charger IC does not have inbuilt protection as there is a conduction path through the body diode of the LSFET, and external protection would have to be implemented for plugging in battery in reverse: www.ti.com/.../slva139.pdf

0 Zhonghui Xu over 3 years ago in reply to Kedar Manishankar

TI__Expert 5445 points

Hi Kedar,

Thanks for the replay.

1)Is there any application note or reference design for "sys hanging off of PMID"

2) If I keep a PFET in between battery and SW pin, then does it effect the charging current direction?

Thanks a lot.

Best regards,

0 Kedar Manishankar over 3 years ago in reply to Zhonghui Xu

TI__Mastermind 24075 points

Hi,

You can refer to BQ25302 datasheet section 9.2.2 Typical Application with External Power Path. It has same topology as BQ25306.

0 Zhonghui Xu over 3 years ago in reply to Kedar Manishankar

TI__Expert 5445 points

Hi Kedar,

Understood. But what about reverse polarity protection? External power path won't fix that issue right? How to do reverse polarity protection without effecting battery charging and discharging cycle?

Thanks a lot.

Best regards,

0 Kedar Manishankar over 3 years ago in reply to Zhonghui Xu

TI__Mastermind 24075 points

Hi,

You can refer to the app note linked in the first post. It shows how to implement reverse polarity protection.

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BQ25306: Issue on output side when battery is not attached