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BQ25710: Primary battery and other integration questions

MMx
Intellectual 300 points
Part Number: BQ25710
Other Parts Discussed in Thread: BQ40Z50

We are developing a device that is powered from USB-PD and may also source back to a compatible USB-PD accessory.

The device will feature a Li-Ion battery (3S) or alternatively primary batteries (6x CR123 --> 9-18.8V, 6x L91 --> 5.4-10.8V) which may be connected instead of the rechargable battery in the same mechanical slot.

Is it possible to use BQ25710 with primary cells while ensuring that charging is prohibited using CHRG_INHIBIT=1?

If yes can you use the sensing resistor in the battery path to measure the amount of energy drawn and thus estimate the remaining battery life?

Am I understanding correctly that I could set the charger current to zero thus discharging the battery while operating the device instead of drawing power from the supply (which may be a power bank style limited source).

As I am new to the whole SMBus topic I was wondering if this charger works when directly connected to a battery. Would I typically add battery, controller and charger on the same SMBus and both masters (battery and controller) give instructions to the charger, or would I connect the controller to the battery on one bus and connect the controller to the charger on a separate bus?

I miss the option to connect a battery NTC line to the charger... Would I need to use an ADC in the controller to surveil this feature?

  • 0
    TI__Mastermind 32745 points

    BQ25710 supports multi-chemistry batteries. Charging stops when you write 0 to charge current register or enable CHRG_INHIBIT=1. BQ25710 works with a battery gauge who estimates the battery capacity, such as BQ40Z50. 

    LEARN function allows the battery to discharge while the adapter is present. SMBus uses address to identify each device, thus allowing multiple devices on the same bus. 

    There is a independent comparator inside the BQ25710. You may use this feature for surveillance. 

  • 0 in reply to Tiger Zhou
    Intellectual 300 points

    Thank you for the feedback, I have still some questions regarding the use with rechargable batteries (1) and primary batteries (2):

    1.

    Thank you for the reply. Is it correct that the charger directly listens to the 0x14/0x15 commands from the smart battery and sets the charging voltage/current without system host interaction? So the system host will only have to configure the charger initially and if necessary prevent charging if a primary battery without SMBus is present.

    I noticed that other SMBus battery chargers (that don't offer the buck-boost and USB-PD features) often include connectivity to the batteries NTC safety signal. Did I see correctly that BQ25710 has no such interface and the system host would have to check this signal and inhibit charging if the battery gets too hot?

    2.

    Do you have any experience with connecting primary batteries to this device? Will charging inhibit completely disable charging or is there any chance a trickle charge may still flow into the battery?

    As learning is not possible with primary batteries, does the charger support the measurement of how much capacity has been removed from the battery or would I have to continually surveil the analog current output pin to get this information?

  • 0 in reply to MMx
    TI__Mastermind 32745 points

    It is true that BQ25710 directly listens to charge current /voltage registers 0x14/0x15. It also has AUTO_WAKEUP_EN by default to charge a dead battery. BQ25710 is a host-driven battery charge controller. 

    Charge_inhibit completely stops charging, there is no switching signal. The part won't know the state of charge status, it is designed to work with a battery gauge.

  • 0 in reply to Tiger Zhou
    Intellectual 300 points

    Is there any application note available on how to surveil a smart battery temperature (NTC) signal when using BQ25710?

    What do you mean with "designed to work with a battery gauge"? Is there any application note / schematic available for this?