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BQ25713: About VSYS Internal Resistor Value

NAIM OTHMAN
Intellectual 270 points

Part Number: BQ25713

Dear TI Team,

May I know the internal voltage divider resistor value  at VSYS pin of BQ25713?

Pin No 22 in page 22 block diagram.

http://www.ti.com/lit/ds/symlink/bq25713.pdf

For safety reason, we want to add 10Ω limiting resistor series with this pin.

I think it will not have significant effect to voltage regulation, can you clarify?

Thank you.

Naim

  • 0
    TI__Expert 3320 points

    Hi Naim:
        

        The internal voltage divider is much higher than 10Ohm for sure. By adding 10ohm series with pin 22, you will not have regulation issue. 

    Regards

    Shishuo

  • 0 in reply to Shishuo Zhao
    Intellectual 270 points

    Hi Shishuo,

    Thanks for the reply.

    There is a change of specification.

    Vsys is approximately 17V, and there is need to ensure the limiting resistor can withstand even if 17V is applied across it.

    So we plan to change this 10Ω to 10kΩ.

    And same goes to SRP & SRN pin which currently has 10Ω series resistor.

    As summary of my questions;

    1) How much will it affect regulation if we add 10kΩ to vsys? Is it permissiable? Can we tune the output by adding offset(In that case how many volts)?

    2) Is it ok to change 10Ω to 10kΩ at SRP and SRN pin? If not what is the maximum permissabel value?

    Best Regards

    Naim

  • 0 in reply to NAIM OTHMAN
    TI__Expert 3320 points

    Hi Naim:
        

       Thanks for your explanation. I believe our part can support up to VSYS 19.5V under 4S case. How many cells for your application? If it is 4S, I don't see any issue without current limit resistor you want to add here.

     

       Would you please help me clarify your motivation for this current limit? 

    Regards

    Shishuo

  • 0 in reply to Shishuo Zhao
    Intellectual 270 points

    Hi Shishou,

    It is related to IEC62368-1 fire enclosure requirement.

    The battery used is PS3 level, and all device directly connected to the battery need to be cover with enclosure.

    We dont want to cover BQ25713, it will affect product size.

    So by adding limiting resistor between main line and the device, we can exclude it from fire enclosure requirement.

    Is it ok to add 10kΩ to SRP, SRN and SYS pin?

    Thanks

    Naim

  • 0 in reply to NAIM OTHMAN
    TI__Expert 3320 points

    Hi Naim:
       

        We don't recommend to connect 10k resistor to SRP, SRN and SYSPIN. The page 22 picture is just a highly simplified diagram the internal circuit is much more complicated. The addtional 10k may influence the sensing accuracy and loop stability. 

    Regards

    Shishuo 

  • 0 in reply to Shishuo Zhao
    TI__Expert 3320 points

    Hi there,

    We haven’t heard back from you. We are assuming you were able to resolve your issue. If not, just post a reply below or create a new thread if the thread has locked due to time-out.

    Regards,

  • 0 in reply to Shishuo Zhao
    Intellectual 270 points

    Hi Shishuo,

    Thanks for the clarification.

    Regards