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BQ24610: Charge Timing vs Termination

steve wenner
Expert 2355 points
Part Number: BQ24610

Good afternoon....

I have reviewed the datasheet and still have questions......

With respect to the above part:

1.  Can you tell me does the Charge Timeout work on the Constant Current phase only or over the whole cycle?  I am confused as to how to tie the TTC pin and whether or not to place a capacitor there for charge timeout....

2.  What is the difference between Charge Timeout and termination?

3.  Also I have set the Iset1 to 7.875A...The load may draw up to 3.5A....The part mentions that it is capable of charging up to 10A....Is it safe to say that the load current is NOT part of this 10A path?  ...and secondly is it safe to say that if I place a low inductance in there (say 4.7uH) such that I have a ripple current of 4A which yields a peak of 12A on the battery charging side that I will be safe to not damage the part?

Sincerely,

Steve

  • 0
    TI__Mastermind 24075 points

    Hi Steve,

      There is a separate non configurable inbuilt 30 minute precharge timer, and apart from that there is the fast charge safety timer which can be configured using the TTC pin. The safety timer is a secondary protection which will disable charge and report a fault if the charger does not terminate within the safety timer range. 

    Charge termination is to ensure that the battery is fully charged, and cut off charge to accurately charge battery to set charge regulation voltage, and not over/under charge the battery. Termination is detected while the voltage on the VFB pin is higher than the VRECH threshold AND the charge current is less than the ITERM threshold. A precharge safety timer is often used to detect whether the battery has an internal short circuit. The safety timer can trigger a warning signal to be sent to the end user if the battery could not charge to VLOWV within the specified precharge time period. The fast-charge safety timer provides another level of protection, terminating the battery charging if the timer expires due to an unexpected system failure.

    The system load depends on how you connect it. If it hangs off the battery then the system load will count as part of the charging current. If you are using the powerpath feature of this charger, i.e you have a PFET driven by BATDRV between SYS and BAT, then SYS will be directly supplied by adapter, and charge current will be charged through the switching  Assuming you have the second option of connecting system load, then there is no issue, as the SYS load will be supplied directly through the adapter. The 10A limit is specified more because larger FETs with higher Qg (gate charge) are required which could possibly not be driven by our internal gate drive (HIDRV and LODRV)

    W.r.t inductor ripple most designers choose to design ripple between 20%-40% of max charge current, and this allows them to choose an inductor with saturation current of atleast max charge current + 0.5*ripple. Again this is a tradeoff the engineer must make with regards to ripple current vs size of inductor.