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BQ25895: Problem in finding RC Settable option.

RAJARSHI ROY
Prodigy 140 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ25606, BQ24610, TPS63000, TPS61230, TPS54494

Hello Everyone,

I was looking for a 1S LiPo/L-ion battery charging IC with Standalone(RC Settable) control interface which has a charging current output of 4-5A. I found the BQ25895 which is supposed to have both the feature (I2C and RC Settable) but I was unable to find the RC Settable setting option in the datasheet. Also, I've checked a few other ICs too and and found the same problem in each of them. Can anyone help me understand why the RC Settable option is given as a control feature in the IC selection tool but not in the actual datasheet? (refer the pic for details). Also, if I want a Standalone IC , what other options do I have?

  • 0
    TI__Guru**** 157141 points

    Hi Rajarshi,

    The ICs above function standalone but only with the default charge current (2.0A) and voltage (4.2V).  The input current limit is RC settable.  For a standalone charger with 4.5A charge current, you could use two BQ25606 standalone chargers in parallel or change to a controller with external FETs like BQ24610.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 140 points

    Hello Jeff,

    Thanks for the prompt reply. Actually my application was kind of like this:(Please refer to picture for details). Can you suggest some relevant ICs/ application diagrams by which I can achieve this?  

  • 0 in reply to RAJARSHI ROY
    Prodigy 140 points

    Hello Jeff,

    Another thing I wanted to ask, you suggested that I can use two BQ25606 ICs in parallel for getting my desired output. Did you suggest something like this?(Please refer to picture for details).

  • 0 in reply to RAJARSHI ROY
    TI__Guru**** 157141 points

    Hi Rajarshi,

    I checked with my manager and we cannot recommend tying the two SYS pins together on any of our chargers with 1 shared battery or with 2 separate batteries.  With 1 share battery, the issue is as follows. The SYS pin regulation has a wide regulation range and will not be the same between ICs.  So, without adding quite large ballast resistors in series from each SYS pin to the system load, there is no way to ensure that the 4.5A load is evenly shared between the 2 buck converters.  This would result each converter alternating in and out of thermal regulation, which would cause an oscillation on the SYS output.  With 2 separate batteries, there is the additional problem of uncontrolled charge current flowing from the higher regulating charger to the lower regulating charger, when both batteries are above MINSYS.  I apologize for recommending this.

    The BQ25895 can provide 5-A to SYS from VBUS=12V but the charging current to a 1-S BAT is default set to 2A.  Without I2C, you cannot change the charge current.  You could use 2 separate batteries and chargers, like BQ25606 and then 2 separate ICs, connected to each charger SYS output, like TPS63000 buck-boost for 3.3V/3.5A and TPS61230 for the 5V/2A output. 

    For highest charging efficiency, I suggest you use a single 2-S battery and charge with BQ24610 controller and external FETs.  Th BQ24610 does not provide NVDC power path like BQ25895/606 but does provide power-path selection of either the battery or input 12-V to the system. Then from the system output you can use the TPS54494 dual buck converter to provide 5-V/2A and 3.3V/3.5A.

    Please double check my part selections for the buck and buck-boost ICs as I haven't recently supposed these.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 140 points

    Hi Jeff,

    Let me check on the parts suggested and then I'll be able to decide what kind of topology we'd want to use. Thanks again for the prompt reply. :)

    Regards, 

    Rajarshi