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BQ27531-G1: BI/TOUT pin

K.Yaita
Guru 29720 points
Part Number: BQ27531-G1

Hi Team,

I would like to ask about BI/TOUT pin.

I undersand it is battery insertion detection input but how to detect battery insertion?
The datasheet shows the following and I believe the pin should be pulled up to VCC that isn't battery voltage through 1.8MΩ.
I couldn't understand why BI/TOUT can detect battery insertion with this connection. 



I would also like to know how to connect BI/TOUT and TS if we use internal temperature sensor.
May I have your advice?

(datasheet page 11)
The external temperature sensing is optimized with the use of a high-accuracy negative temperature coefficient
(NTC) thermistor with R25 = 10.0 kΩ ±1%, B25/85 = 3435 K ±1% (such as Semitec NTC 103AT). The fuel gauge
can also be configured to use its internal temperature sensor. When an external thermistor is used, a 18.2-kΩ
pullup resistor between the BI/TOUT and TS pins is also required. The fuel gauge uses temperature to monitor
the battery-pack environment, which is used for fuel gauging and cell protection functionality.

Best Regards,
Yaita

  • 0
    TI__Guru** 105760 points

    Hello Yaita,

    When the internal temperature sensor is used you do not need to populate the components in the schematic examples it is best to ground any inputs that are not used, I also attached the image. If you plan to use the battery insertion function then you will still need to populate the components, the gauge pulses the pin to determine if the battery was inserted.

    From the TRM:

    6.3.1 Battery Detection Using the BI/TOUT Pin During power-up or hibernate activities, or any other activity where the fuel gauge needs to determine whether a battery is connected or not, the fuel gauge applies a test for battery presence. First, the BI/TOUT pin is put into high-Z status. The weak 1.8-MΩ pull-up resistor keeps the pin high while no battery is present. When a battery is inserted (or is already inserted) into the system device, the BI/TOUT pin is pulled low. This state is detected by the fuel gauge, which polls this pin every second when the gauge has power. A battery-disconnected status is assumed when the fuel gauge reads a thermistor voltage that is near 2.5 V.

    Image from the EVM guide:

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Guru 29720 points

    Hi Wyatt-san,

    Thank you for your reply.

    Can we use battery insertion function with internal temperature sensor is used?
    If the answer is yes, I want to know how to connect BI/TOUT and TS in this case.

    Note)
    I would like to know if internal temperature sensor can be used with 10kΩ resistor is populated instead of thermistor in your schematic. 
    May I have your advice?

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru** 105760 points

    Hello Yaita-san,

    Yes you can use the battery insert function still, when the battery is inserted the BI pin must be pulled low.

    Yes that's that would be the equivalent.

    There's some more information on this thread: e2e.ti.com/.../2238741

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Guru 29720 points

    Hi Wyatt-san,

    Thank you for your reply.
    Is it okay to leave TS pin unconnected if we use internal temperature sensor?

    Best Regards,
    Yaita 

  • 0 in reply to K.Yaita
    TI__Mastermind 19195 points

    Hi Yaita,

    As long as IC is close to battery to get accurate temp reading this is fine.

    Best regards,