• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 62 subscribers
  • Views 244 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ78350: BQ78350+BQ76920 connect MCU problem

Star Xu
Genius 9645 points
Part Number: BQ78350
Other Parts Discussed in Thread: BQ76920, ,

Hi 

The customer design with BQ78350+BQ76920. They used BQ76920+BQ78350 with five 18650 batteries in series. When the battery pack is connected to the main board, it is easy to burn out the MCU under the condition of output protection. At this time, they monitored the temperature on the resistance at the SMB line of the BQ76920+BQ78350 battery management board , and found that the temperature kept rising, This indicates that the current on the SMB line is very high. What is the cause of this?

Attached the schematic for your reference.

电池组.pdf

where P2 interface is the interface with the battery pack, and the GND of P2 is disable.

Waiting for your reply.

Thanks

Star

  • 0
    TI__Guru* 77283 points

    Hi Star,

    This schematic does not show very much - it only shows the pull-up resistors for the SMB_CLK and SMB_DAT. Maybe it is possible something is shorted near the P2 connector - the power connections (BAT+ and PACK-) are sharing the same connector with the SMBUS pins.

    Regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Genius 9645 points

    Hi Matt 

    Thanks for your help.

    This is part of the MCU circuit in the motherboard. The MCU and battery pack pass through SMB_ CLK、SMB_ DAT connection.

    Test conditions: A five 18650 series battery connected to the motherboard (through P2 interface, namely, BATT+, PACK -, SMB_CLK, SMB_DAT, etc

     ASCD Threshold and Delay are all set to 0. The battery output is protected ( short circuit protection). If the battery pack is connected to the motherboard for a few minutes, the MCU will burn out.

    They increased the resistance (R36 and R38 in the figure below) on the SMB line (both changed to 510R), which is reproduced under the same conditions

    Please give some suggestions about this problem.

    Thanks

    Star

  • +1 in reply to Star Xu
    TI__Guru* 77283 points

    Hi Star,

    I do not see anything in the schematic that explains why the microcontroller is getting damaged. I do not think this is caused by the SMBus lines since these lines are driven by the STM32 (host) and not the BQ78350-R1A. They need to figure out where the damage is occurring on their microcontroller and why. I do not think this is related to the TI devices.

    Regards,

    Matt

  • 0 in reply to Matt Sunna
    TI__Genius 9645 points

    Hi Matt

    Thanks for your help.