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BQ25895: BQ25895 VBUS

Hao Nguyen
Prodigy 10 points
Part Number: BQ25895

Regarding the IC BQ25895, I'm using this IC to power management which managed by MCU and provide power for Linux board.
I noticed that when I use the battery and connect a 12V input source, the measured VBUS is approximately 11.3 ~11.5V. However, when I disconnect the battery, the power measures around 11.8V. Could someone clarify why this is happening?

  • 0
    TI__Mastermind 32020 points

    Hello, 

    Thank you for reaching out via E2E. Can you please share where on your board and how you are measuring VBUS voltage?

    Assuming the measurement is taken near the VBUS pin on the BQ25895 IC you are mostly likely observing a lower VBUS voltage with the battery connected because the current draw is higher when the IC provides power for the Linux board and charges battery compared to just powering the Linux board. 

    With the input current draw increased the voltage drop across the cable/PCB trace from input source to VBUS will be larger. One way you could confirm this theory is measure VBUS with the battery attached, but with charge disabled. In this case I would expect VBUS to be approx. 11.8V rather than ~11.3-11.5V. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Thank you for your prompt response! Currently, I am utilizing an MCU by Atmel SAML21E to oversee BQ25895 and a Linux board with an Ambarella chip. My method of measuring VBus is by reading the register of REG11.
    "but with charge disabled. In this case I would expect VBUS to be approx. 11.8V". You are right.

    For the VBus levels when a low percentage battery is connected, they typically range between 11.3-11.5V.

    Thank you!

  • +1 in reply to Hao Nguyen
    TI__Mastermind 32020 points

    Hi Hao, 

    Thank you for the additional explanation. The reduction in VBUS is due to the increased current draw. 

    Please let me know if you have any additional questions. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Hi, Thank you!
    Till now it clear to me.