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BQ24250: Powerbank Battery Management, Fuel Gauge, Charger simple solution

Simon Gast
Prodigy 80 points
Part Number: BQ24250
Other Parts Discussed in Thread: BQ27532-G1, BQ25895

Hi Team, i hope you can help me choosing the right ic's for circuit planning.

The application (Powerbank) needs the following features:


-Charging 1 Lithium Battery (3,7V/4,2V) with max. 2A (not removable/changeable) (at least 1A charging current)
-Power Path Management (support the system (load) with 5V power, while Battery is charging with less than 2A -> maybe remaining current from the 2A charging current)
-measuring state of charge with at least 10% accuracy, not sure if impedance track is necesarry for that, 4-6 LED displaying the State of charge
-only operate when load is added
-only QFP, QFN, DFN, SOP, SOIC or PLCC Packages

-optional integrated step up boost DC-DC converter for converting the Batteryvoltage to USB-Voltage 5V (Powerbank Output) at min. 1 - max. 2 A charging current

I already found the BQ27532-G1 with the BQ2425x for that application, but the BQ27532 is only available in DSBGA Package in Germany, witch is not an option.
Maybe you can recommend one or even multiple IC's for that application.
Is there a Solution where i dont need an additional microcontroller for driving the LED's?

Thanks for your help preaviously
with kind regards from Germany

Simon

-

  • 0
    TI__Guru**** 167196 points
    Simon,

    Have you considered bq25895 in QFN? It was designed for powerbank. It has integrated 7-bit ADC which can be used to read the battery voltage. It will automatically switch to boost from battery back to PMID pin when VBUS is removed (after a short delay).
  • 0 in reply to Jeff F
    Prodigy 80 points
    Thank you,
    this one looks very suitable .
    What i am not sure about is the current output charging the device plugged into the powerbank later. Please correct me if im wrong:
    -->For 5V devices charged by the Battery i need another DC-DC converter Boost chip, to transfer the SYS-Voltage to 5V and determine the load and the current drawn by the load.
    -->When i use the Boost charging mode for 5V devies the PMID-Pin is used as an output (OTG-Pin High)
    -->When i disable the Boostmode (OTG PIN control from host) i cant use the PMID-Pin as an output and can use the SYS-Pin for lower charging current

    Can i determine a maximum current for the SYS-Pin where the BQ25895 cut off the output for safety reasons?

    Thanks for your help!
    Simon
  • 0 in reply to Simon Gast
    TI__Guru**** 167196 points

    Simon,

    Please keep in mind that there is only a FET between VBUS and PMID.  So, when VBUS has input power applied, approximately the same voltage appears on PMID. 

    If you need a regulated 5V rail when input power is being applied to VBUS, then yes, you would need to add an external boost converter, powered from SYS.

    If no input power is applied to VBUS, the PMID output provides 5V up to 3A.

    If boost mode is disabled and no power is applied to VBUS, V(SYS) = V(BAT). 

    If by "cut off" you mean the bq25895 has turned off the internal BATFET, isolating the battery from the SYS pin, then you can use the datasheet efficiency curves to predict the buck converter's maximum output power from the input power.  For example, with VBUS=5V and maximum input current of 3.25A, giving input power = 16.25W, you can get output power = 16.25W *~92 = 14.95W.  Dividing that by 4.2V output voltage gives about 3.6A of output current. 

  • 0 in reply to Jeff F
    Prodigy 80 points
    Thanks for your reply,

    Sorry if this is a stupid question but,
    how do i then determine the charging current for the phone? I suppose that the USB connection (D+ and D-) in the example circuit is only to determine the charging current for the battery (connected to BAT) and not for the phone (so this bus only communicates with the adapter plugged in to charge the battery and power the SYS).
    Is therefore an extra IC or cuircit neecssary/responsible, that communicates with the phone to
    set the right charging current, that the phone will draw?

    Thanks for your help
    Simon
  • 0 in reply to Simon Gast
    TI__Guru**** 167196 points

    Simon,

    D+/D- only sets the charger's input current limit until the host is up and running, in order to be prevent crashing the input power supply.  Using efficiency power balance, eff=Po/Pin= 4.2V*(ISYS+IBAT)/(VBUS*IBUS), where ISYS is your expected maximum system current, IBAT is your desired charge current and IBUS is the input current being limited by D+/D-.  For example, if D+/D- detects an unknown 5-V adapter and sets input current limit to 500mA, I recommend that your system will not pull more than 92%=4.2V*ISYS/(5*500mA) in order to prevent supplement current from the battery until the host is up, can enumerate the USB lines and get the real USB power and then hopefully increase the charger's input current limit and/or charge current.

  • 0 in reply to Jeff F
    Prodigy 80 points

    I did understand that.
    Still im not sure how the PMID is used charging the PHONE.

    My circuit is for a powerbank... and the plan is to connect the SYS Supply to power the microcontroller (HOST) for now it shall be e.g. a ATtiny2313 driving some LED's and communicate via I²C with the BQ25895.

    So i assume that i could connect a smartphone via USB VCC to the PMID pin (charging the PHONE or better the battery of the phone with 5V up to 3.1 A) and the Ground of the SYS. The D+ and D- Pins (not of the BQ25895 but of the Smartphone/Cable) determine the charging current the Phone will draw from the BQ25895 through the PMID pin.
    So how can i determine this charging current for the Battery in the Phone (I read that this is controlled by resistors connected to D+ and D- of the phone, or even short the two contacts of the phone!?). Ofcourse i dont mean the current for the Battery connected to the BAT pins of the BQ25895.


    Or shall i even use an additional step up modul connected to the SYS pin for charging the phone?
    There will be only the application of the powerbank to charge one Phone.

    I also got a first circuit set up if this helps to understand my Problem.

    Best Regards

  • 0 in reply to Simon Gast
    TI__Guru**** 167196 points
    The charger works either in charge mode to charge the powerbank battery connected at BAT or in OTG mode to power a phone, etc connected at PMID, not both at the same time. The phone connected at PMID will have a preset low to medium level default charging current. You could write HOST software to communicate with the phone's charger IC at PMID using the D+/D- lines, assuming the phone's charger IC is BC1.2 compliant. This would tell the phone charger the maximum input current from the powerbank output (895 PMID pin) that it can expect. The powerbank charger IC does not use the D+/D- in OTG mode.

    Alternatively, if you do not want to use charger's OTG mode, you can add an external boost converter connected at SYS. There are a few powerbank designs like this at www.ti.com/tidesign.
  • 0 in reply to Jeff F
    Prodigy 80 points
    Thanks, i realy just needed those examples to be sure of what i am doing there.
    This helped alot!