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BQ25606: Efficiency is 85% instead of 93% and Vsys unstable when battery is not connected

Emilija Zukauskaite
Expert 1100 points
Part Number: BQ25606

Hi,

I measured the efficiency and its not as eXpected.

I supply 5V input and it draws 423mA.

The battery is charging at 480mA and battery voltage is 3.75V.

I calculated the efficiency to be 84%. 3.75*0.48/5*0.423 * 100 = 84%

Datasheet shows that at 5Vin 0.5A and inductor DCR is 18mR the efficiency is 93-94%. Where am I losing the efficiency? Is it because my inductor DCR is 90mR?

I also not sure what the system output fluctuates from 3.8V to 4.2V when the battery is not connected?

Thanks!

  • 0
    TI__Genius 16105 points
    Hi,
    For efficiency measurement result, can you also try lower inductor DCR value? Based on your DCR, I think the efficiency may have 5% different based on my quick calculation.
    And is there any system load during your measurement?

    When battery is not connected, can you try to disable charger at first then check your system voltage again?

    Thanks
  • 0 in reply to Paul Yeh
    Expert 1100 points

    Hi Paul,

    Thank, I will try a different inductor next time I order the parts.

    I have a dc-dc converter connected to the output of the charger circuit from ~4V to a fixed 5V. No load.

    I won't be able to disable a charger for my application. Do you think there will be any issues if I connect the output and step up to 5V? The 5V output of the dc-dc looks stable even though the input oscillates.

    I read questions about this part and at least 5 people asked about this oscillation when the battery is not connected. I think the datasheet should mention that and warn. At the moment the datasheet just says that it has an instant on feature and I would expect to get a stable output.

    Thank you for your help!

    Regards,

    Emilija