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BQ25505: BQ25505 Cbat reduction

Stefano Contini
Prodigy 75 points
Part Number: BQ25505

Good Morning,

question is about the possibility of reduction of capacitor on Vbat_sec. To manage my load I use only Vstor output, but i have to respect a total capactior limit connected to BQ25505 for Atex certification.

Can I remove Cbat_sec and connect the pin to GND or insert a capacitor 1/10 uF maximum?  I could have DC/DC stability problems?

Regards, good job

Stefano.

  • 0
    TI__Intellectual 2050 points
    Hi Stefano,

    Are you using the bq25505EVM?

    What is the total capcitance limit you need to meet?

    -Joe
  • 0 in reply to Joe Stephan
    Prodigy 75 points
    Hi Joe,
    thanks for you answer.
    Total capacitance around the component have to limit to 55 uF for this type of certification, actually I place around 10 uF of total capacitance without consider Cbat.
    I want to understand if it is possible reduce this cap (< 47 uF ca) without compromising the DC/DC stability.

    Thank you and good job

    Stefano.
  • 0 in reply to Stefano Contini
    TI__Intellectual 2050 points

    Stefano,

    Stefano Contini said:
    Hi Joe,
     
    I want to understand if it is possible reduce this cap (< 47 uF ca) without compromising the DC/DC stability.

    No, the stability of the DC/DC will depend on the capacitance on VBAT. I do not recommend doing this. Testing that was done for this device determined 100uF as the minimum.

    If you decide to reduce it, do not expect the device to be as stable.

    -Joe

  • 0 in reply to Joe Stephan
    Prodigy 75 points

    Ok Joe, thank you so much.

    The last answer is:

    Is possible to short-cirtcuit Vbat_sec and Vstor? Because I've to use only one of this outputs to supply my load.

    In photo, you can see the situation.

    I'm open to evalue other ideas for this schematic,If you have any.

    Regards, good job.

  • 0 in reply to Stefano Contini
    TI__Intellectual 2050 points

    Stefano,

    I do not recommend shorting VBAT_SEC to VSTOR. This will bypass the internal FET which is used to protect the battery from over charge/discharge.

    Also, the FET is used to connect VBAT_SEC to VSTOR once VSTOR reaches the BAT_UVLO threshold. If they are shorted together, the VSTOR will alwasy be connected to the battery, which may delay the Boost charger from reaching its optimal efficiency state.

    What is the equivalent capacitance of your battery? Depending on what that is, you may be able to reduce C3.

    C3 + BAT_equivalent_capacitance = 100uF should be okay.

    -Joe

  • 0 in reply to Joe Stephan
    Prodigy 75 points
    Joe.
    I resolved my problem with the last test.

    Thank you for support.

    Good job