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Original question:

BQ25792: BQ25792 HEAT about

BQ25792: Heat Dissipation, Estimation and Recommendations

Hassan Hafeez
Prodigy 40 points
Part Number: BQ25792
Other Parts Discussed in Thread: TPS25750, , BQ25756

Tool/software:

I have a prototype PCB with TPS25750 and BQ25792 charger. 


Battery is 3S and charging current is 2A. 

The BQ gets quite hot and stop charging after just 10 seconds. I tried placing heatsinks etc on it but no avail. 

In the first iteration of the board, I had no ground polygon pours around the device in top or bottom layer. the inner layers had ground pours. the SW nodes had similar pours as in EVB. 

In the second iteration of the board, I have placed many suitably sized vias for heat dissipation and I wanted to be sure before manufacturing. 

Since the board is part of an embedded device, How can I ensure proper heat dissipation besides more plane area around the BQ? if any other part is recommended, pl let me know. 

I am attaching the pictures for layers 1, 3, 4, 6. 2 and 5 are ground planes. 

Layer 1:

Layer 3:

Layer 4:

Layer 6:

Lastly, how can we estimate heat dissipation for the BQ?

  • 0
    TI__Mastermind 32771 points

    Hello Hassan,

    I'm reviewing your layout, I will provide an update after I gather more information.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    TI__Mastermind 32771 points

    Hello Hassan,

    I don't see any obvious issues with the layout,

    Hassan Hafeez said:
    I have placed many suitably sized vias for heat dissipatio

    This will hep improve heat dissipation.

    Hassan Hafeez said:
    Lastly, how can we estimate heat dissipation for the BQ?

    We don't have a way to estimate the heat dissipation.The datasheet thermal table has RthetaJA in degrees C/W which can be used to estimate the chip heating but it is only helpful if the PCB is of a very specific type and size.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 40 points

    Hi Christian! 

    Thank you for the reply. 

    I saw a post where someone from TI estimated some temperature. would you be able to help me estimate the temperature keeping the reference design with TPS25750 and BQ25792? assuming my PCB is the same size as that?

    How can one estimate temperature using the provided RthetaJA?

    Furthermore, Can you recommend any other charging ICs that are not so sensitive to temperature? The embedded device this PCB is being designed for is supposed to be an industrial device with ambiend temperatures of ~50C. I chose the BQ25792 for dual input selection and charging capabilities but I am facing a lot of difficulties related to heating. 


    Would you recommend I move the desgin to power muxes such as the TPS259470x for input power selection and the BQ25756 with external FETs for charging?

  • +1 in reply to Hassan Hafeez
    TI__Mastermind 32771 points

    Hello Hassan,

    Hassan Hafeez said:
    I saw a post where someone from TI estimated some temperature. would you be able to help me estimate the temperature keeping the reference design with TPS25750 and BQ25792? assuming my PCB is the same size as that?

    He estimated the temp based on the BQ25792 EVM, so this measurement would not be accurate. I recommend using the method below.

    Hassan Hafeez said:
    How can one estimate temperature using the provided RthetaJA?

    I recommend refering to this E2E post:https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1311540/bq25792-abnormal-temperature-during-charging/4983724?tisearch=e2e-sitesearch&keymatch=BQ25792%2520RthetaJA#4983724

    Hassan Hafeez said:
    Furthermore, Can you recommend any other charging ICs that are not so sensitive to temperature? The embedded device this PCB is being designed for is supposed to be an industrial device with ambiend temperatures of ~50C. I chose the BQ25792 for dual input selection and charging capabilities but I am facing a lot of difficulties related to heating. 
    Hassan Hafeez said:
    Would you recommend I move the desgin to power muxes such as the TPS259470x for input power selection and the BQ25756 with external FETs for charging?

    I don't think this would be the best option. This would require more rework, and could potentially cause further issues. I think with second the iteration of the board you will see better thermal efficiency.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 40 points

    Hi Christian!

    Thank you for the explanation and the confidence. 

    I will mark the question resolved. If I have any further question regarding this in future, I may come back lol. 

    Have a great day!