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Original question:

BQ25700A: BQ25700Using problem

BQ25708: my design board have very low efficiently，the bq25708 and mos is too hot！

user5141498
Intellectual 380 points
Part Number: BQ25708

hi ti engineer：

            my design board，use bq25708 to charge a 1S3P   18605 battery， now found the  charger have very low efficiently，the bq25708 and mos is too hot！

            i test use a battery in cc mode.  and not have system load

            when set charge current (0x14) = 4A,  the actual input voltage is 19V 1.1A  , the output voltage and charge current i get from bq25708 adc is 4V and 4A   ,  so the efficiently is  16/20.9= 76%

            no mater i set charge current (0x14) = 2A, in cc mode or use a low input adapter 13V ，， the result is all the same.

            charge 3-5mins,  no mater 4A cc mode or 2A cc mode

   the bq25708 is 64°

   HIDRV1 MOS is 74°

   LODRV1 MOS is 64°

  2.2UH  inductor is 50°

  the same condition ， the EVM temprature is good.

  which direction should i to check？ is the layout problem？ thank you very much

1s char.pdf

  • 0
    Intellectual 380 points
    the sch is the 1s char.pdf
  • 0 in reply to user5141498
    TI__Genius 16125 points

    Yanbin,

    I think your board efficiency should be too low. Can you choose lower Qg mosfet in your system board to improve efficiency.

    Our EVM board, the Qg is around 6nC.

    Thanks

  • 0 in reply to Paul Yeh
    Intellectual 380 points

    now i change the mos fet to CSD18534 ，  but There is no improvement， the mos teamperature is 70 °，  Is there any other reason that leads to inefficiency?   thank you

  • 0 in reply to user5141498
    TI__Genius 16125 points

    Yanbin,

    Good day.

    As for efficiency data, 76% is too low, so is it possible there are some other loading during your measurement.

    I saw your board is just 2-layer, I think to use 4-layer board will be better thermal dissipation?

    Thanks

  • 0 in reply to Paul Yeh
    Intellectual 380 points

    hi Paul Yeh：

                 first no other load ， only the charing battery ， the test condition is same as evm.     yes , i think the layout 2-layer maybe is the problem ， the SW1 SW2 HIDRV1 LODRV1 HIDRV2 LODRV2 BTST1

    BTST2 should be as close as possible to the supply of the switching MOSFET ？

                  Previous waveforms is captured at stop mode， now i found at run mode（oscilloscope）， the  Duty cycle regulate constantly，  maybe this is the problem？   the wave at evm is stable at run mode（oscilloscope）.

                  can you tell me The cause of this waveform and its influence.？  

                 now the bq25708 analog ground is not separate from power ground.  and have cause some noise into bq at capture voltage then cause the Unstable duty cycle wave？

                  thank you very much！