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BQ25180: Sourcing the input with backup battery?

Emanuel Soares
Intellectual 530 points
Part Number: BQ25180
Other Parts Discussed in Thread: BQ25620,

Hello,

I would like to know if it's possible/recommended to put a diode between IN input and SYS output of BQ25180YBGR.
The purpose on this is so that the system that power the BQ input is a 5V bus that in certain moment could fall. In case of fall, the battery should source both the SYS pin and the 5V bus (in case of the battery sourcing the 5V, this bus will not be expected to have the 5V level, but the battery's - and this is ok).




Regards,
Emanuel.

  • 0
    TI__Intellectual 910 points

    Hello Emmanuel,

     Thanks for reaching out! This is not recommended.

    When input power is removed, the IC is able to determine if a battery is present thus supplying power to anything loaded on SYS. This mode is called supplement mode. We would recommend to place anything that needs to be powered by the 5V_BUS at the SYS PIN which will then be powered by the battery if the 5V_BUS rail falls. When the IC senses an adapter removal then the internals of the IC will swap power from V_BUS to the Battery, if the concern is the IC register settings.

    From reading your post it sounds like you are looking for a product that does offer OTG (On-The-Go) charging. We do offer some ICs with this feature (ie. BQ25620). With the OTG feature the IC is able to deliver power from the battery to VBUS. 

    BQ25620 data sheet, product information and support | TI.com

    V/R

    Rafael Camarillo

  • 0 in reply to Rafael Camarillo
    Intellectual 530 points

    Hello, Rafael.
    Thanks for your reply.
    I understood your point. Another question I forgot to mention: knowing that the battery is made of lithium-ion, a 5V at the Input pin will manage to recharge it correctly? Or, is there any voltage regulation so that the 5V will be down converted to the battery necessary voltage during recharging cycle?

  • 0 in reply to Emanuel Soares
    TI__Intellectual 910 points

    Hey Emanuel,

    Yes, 5V at the input will charge the battery.
    The BQ25180 is a Power Path linear charger. The linear charger is essentially an LDO and will use the available power to charge the battery according to the battery voltage. Voltage regulation happens inside the IC and VIN will not be effected, unless the IC goes into VINDPM regulation. VIN gets regulated when the input power is not able to source the programmed current for the system load.

    V/R

    Rafael Camarillo

  • 0 in reply to Rafael Camarillo
    Intellectual 530 points

    Hello, Rafael.
    Thanks for your response.
    Another two questions:
    1. Should I place the three PU resistors for the I2C and INT to the SYS pin or to the INPUT pin?
    2. Is it possible to have a information from the chip whether the SYS pin is attached to the INPUT or to the battery? Is there any register that tell me this info?

    Regards,
    Emanuel.

  • 0 in reply to Emanuel Soares
    TI__Intellectual 910 points

    Hello Emanuel,

    1. From your previous screenshot, the three 10K resistors that you have will work were you have them connected. Please consult and review the MCU datasheet to ensure that the pin tolerance is able to handle the voltage that you are applying at those pins.

    2. There is no information from the chip that tells you whether the INPUT power is going to power a load on SYS or to charge the BATT. There are a couple registers that could help in determining what state the IC is in though.

    The first one is the STAT0 register and, CHG_STAT_1:0[5:6] this will tell you If the IC is charging the battery or not, and what mode it is in.

    The second one is the STAT0 register and, VIN_PGOOD_STAT[0] this will tell you if your INPUT power is sufficient.

    V/R

    Rafael Camarillo

  • 0 in reply to Rafael Camarillo
    Intellectual 530 points

    Hello Rafael,
    I meant, is there any register that tells if the SYS bus is being powered by the battery or by the IN?

  • 0 in reply to Emanuel Soares
    TI__Intellectual 910 points

    Hey Emanuel

    There is not a register to specifically tell you what SYS is being powered by.

    The SYS_REG, SYS_MODE_1:0 will allow you to control how SYS powered, but it will not change once you set it. 

    V/R

    Rafael Camarillo