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LOW CURRENT BATTERY CHARGING WITH CELLULAR CURRENT DRAW LOAD

Ben Cotton
Prodigy 70 points
Other Parts Discussed in Thread: BQ24195L, BQ25890, BQ25980

Hi

I am powering a cellular/gps circuit and the BQ24195L handles the pulsed load of the cellular from the battery supply that I have.

The batteries that I have are Tadiran TLI-1550A.

 

In order to meet the charging requirements for multiple cells (in parallel) at -40 deg C, I would need to be able to trim back the fast and termination charge to something like what is available in BQ2512X.

This product will operate at -20 degrees C and below. Is there a product that spans both of these extremes or can someone suggest something like increasing the  SYS current of the BQ2512X to meet a cellular module type current load?

Many thanks

  • 0
    TI__Mastermind 25800 points

    Hey Ben,

    Take a look at the BQ25890/2 products. 

    If you don't use the boost function of the BQ24195L that you're currently using, take a look at the BQ2425x family of parts.

    Typically, if you see '"JEITA Compliance" in our datasheet, our devices will have two extra temperature thresholds that will either throttle back current or voltage. 

    Hope this helps,

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 70 points
    Thanks Joel

    The BQ25980 is certainly better for me than the BQ24195L. With its fast charge minimum of 64mA Vs the 20% of 512mA (102mA) of the BQ24195L.
    The termination is 64mA but I reckon I could disable that and just run a timer on the microprocessor based on battery temperature?

    Thanks again.

    Ben
  • 0 in reply to Ben Cotton
    TI__Mastermind 25800 points
    Hey Ben.

    ITERM is adjustable via I2C as well if that is what you were looking for via REG05, so you could set it to 128mA.

    But your method also works as well if you are monitoring the voltage at the TS pin, you could disable termination with REG07.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 70 points
    Thanks again Joel,

    At -40 deg C my termination charge is down at 10mA so I was reckoning to run on fast charge at 64mA then use the low temperature 20% of fast charge to drop it to 13mA, disable termination charging and start a timer.

    Does it work the way I expect it to?

    Ben
  • 0 in reply to Ben Cotton
    TI__Mastermind 25800 points
    Hey Ben,

    Did you measure that 10mA termination current?

    You can run fast charge at 64mA, but you will have to directly manipulate a resistor divider at the TS pin, unless you know for a fact you will drive below the Tcool temperature.

    Also, driving below Tcool may disable termination altogether, but this is not spec'd in our datasheet. If it does not, then you will have to manually disable termination via the I2C interface as our minimum termination current is 64mA. Be careful too that your FAST charge current is a little higher than our lowest termination current, unless you disable termination during fast charge mode as well.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 70 points

    Hey Joel

    Not measured it yet.

    In my schematic - based on our discussion

    I changed the TS divider as follows: RT1 at 2.26k and RT2 at 6.39k.

    I also changed the output inductor from 1uH to 12uH.(340mA)

    Have a dev kit on order but not got it yet.

    Ben

  • 0 in reply to Ben Cotton
    TI__Mastermind 25800 points
    Hey Ben,

    Do you plan on also having the NTC?

    What temperature do you plan on running the battery under to achieve the Tcool threshold?

    Either way, having ICHG (fast charge) exactly at the termination current is going to be tricky. You would have to disable charge termination for the entire process.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 70 points
    Hey Joel

    Yes, using the 103AT 10K NTC.

    T1: -40C
    T2: 7.8C
    T3: 65C
    T5: 85C

    Thats what I believe that I have with the new RT1 and RT2 values.

    Thanks

    Ben
  • 0 in reply to Ben Cotton
    TI__Mastermind 25800 points

    Hey Ben,

    At T1, all charging will stop, so assuming you calculated the values correctly, at -40C. 

    At T2, according to the picture below (this is for the BQ25890), the charge current will go down to the 20%_FastCharge. Thiat is driving the device into Tcool region, which automatically disables termination.

    While you are between T2 and T3, the device will keep termination enabled (unless you disable it), which is at 64mA. So unless you drive the device into the Tcool region, your FastCharge may have to be a bit higher. 

    Also, make sure the battery specs match what you need (-40C to 85C) in terms of charging region.

    Regards,

    Joel H