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BQ21080: The heating problem of the chip

Tonyx.wu
Expert 2735 points
Part Number: BQ21080

This charging chip BQ21080YBGR inputs 5V 220mA to charge one lithium battery. The battery voltage is 3.1V, and the device will generate heat. The current is only two to three hundred MA, so what's going on? After the charging current slowly decreases, it will not be hot.Can you help me see where the problem is?

Software configuration:

schematic diagram

Watchman_MB_V2.0.pdf

LAYOUT:

Watchman_MB_V2.0_PCB_20230901_1735.pcb


  • 0
    TI__Intellectual 910 points

    Hey Tony

    While we look over the pcb file attached, would it be possible to get a full register dump, to assist us in troubleshooting?

    V/R

    Rafael Camarillo

  • 0 in reply to Rafael Camarillo
    Expert 2735 points

    The register log is supplemented as follows:

  • 0 in reply to Tonyx.wu
    TI__Intellectual 910 points

    Hey Tony

    Thank you for the information. When looking at the STAT0 register (THERMREG_ACTIVE_STAT [1]=0) bit is not set. This means that there is no thermal regulation happening. Would it be possible to measure the battery voltage when the current starts to drop? This would help us determine if the device is in Constant Current or in Constant Voltage mode. Would it be possible to elaborate on heat? Is this "heat" due to the IC or due to other factors on the PCB?

    We have been trying to open the .pcb file that was sent but have not been able to. Would it be possible to send the gerber files?

    V/R

    Rafael Camarillo

  • 0 in reply to Rafael Camarillo
    Expert 2735 points

    Watchman_MB_V2.0_gerber.zip

    gerber files As attached, please check.Could you please provide a solution for all the problematic areas on my end? Thank you！

  • 0 in reply to Tonyx.wu
    TI__Intellectual 910 points

    Hey Tony

    When looking at the information and settings provided it appears that the device is operating within the expected temperature range.

    We have been looking at the gerber files submitted and have not noticed any thing that stands out. We do recommend improving copper pours for better heat dissipation. 

    V/R

    Rafael Camarillo

  • 0 in reply to Rafael Camarillo
    Expert 2735 points

    Is there anything else that needs improvement in all the information submitted? The current issue here is urgent. Could you please take a look again? Thank you!

  • 0 in reply to Tonyx.wu
    TI__Mastermind 23220 points

    Hi Tony,

    Due to the nature of the BQ21080 being a linear charger, any power dissipation gets dissipated as heat. 

    Based on this duplicate thread that I was initially supporting: BQ21080：Power management forum - Power management forum - Power management - TI E2E support forums, the concern is that the charger goes up to 50-60 degrees. This is within the expectation of operation on a board like you've provided.

    The following are images of our charger operating at 300 mA and 400 mA respectively at 3.7 V battery. 

    This is on a board designed with thermal in mind and why Rafael has recommended larger copper pours. At 3.1 V battery @ 200 mA I would expect 100 mW more dissipation and based on the thermal resistance I've provided below, I would expect 10C.

    The recommend solution if larger copper pours is not possible is to reduce power dissipation from the input to the battery which would mean reducing your charge current which you've seen reducing the temperature.

    Please refer to 8.3.7.7 Thermal Protection and Thermal Regulation in the datasheet for more considerations for thermal. 

    Best Regards,

    Anthony Pham