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BQ25895: What is continuous output power of BQ25895

Rahul Surawase48
Expert 2395 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ24610, TPS61088, BQ27542-G1, BQ24773

Hello TI, 
             We are worried about BQ25895 Output power rating, we are looking for 5V/4.5A system output what is the maximum System Output power of BQ25895 

1. Adapter Input 5.5V/5A  (BQ25895 Input source)

2.Required power path management feature to auto switch Adapter power(Fails) to Battery power, Can BQ25895 provide this feature ..?

3.What is the Maximum continuous System output power of BQ25895 ..? 

4. What we need to give power the system PMID or SYS pin ..?

Thanks, 

Rahul Surawase  

  • 0
    TI__Guru*** 143850 points

    Rahul,

    Maximum output power to SYS (including charge current from SYS to BAT) is 5A x 4.608V = 23W.  The 4.608V is assuming the BATREG is set close to this value; however, with a 4.2V LiIon battery, VSYSmax is 4.3V.  The input current maximum is 3.25A so with only 5.5V input, your maximum output is approx. 3.25A*5.5V*0.92 = 16.4W. 

    To achieve this much output power, the IC's package will need a large, exposed GND copper plane for heat sinking and possibly air flow. 

    If input power fails, the BATFET automatically turns on to provide power to SYS.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2395 points

    Hello Jeff,

                    Consider the Continuous Output Power to system is 16.4W, what is my maximum Battery charging current..?

    1.On 16.4W Output Power, my Max charging is current is 1.75..?

    2.Can you clear the difference of PMID and VSYS ..?

    3.VBUS ON - VSYS = 4.6v and VBAT ON & VBUS OFF - VSYS = 4.3 ..right ..?

    4.For Maximum output power to SYS (including charge current from SYS to BAT) is 5A x 4.608V = 23W, what is recommended  Input source Power rating (Adapter rating)

                           Thanks for quick responses and valuable support 

    Thanks, 

    Rahul Surawase 

  • 0 in reply to Rahul Surawase48
    TI__Guru*** 143850 points

    Rahul,

    Regarding 1, assuming no SYS load, 16.4W/4.2V = 3.9A.

    Regarding 2, PMID is connected to VBUS through a FET that provides reverse blocking and measures current.  So when VBUS is applied, V(PMID) = VBUS - IBUS*Rdson.  Any current taken from PMID is not available to the buck converter for SYS load and BAT charge current.  PMID is also the output when the buck converter operates in reverse, powered from the battery, as a boost converter to provide V(PMID)=5V in OTG mode. 

    Regarding 3, With VBUS applied, V(SYS) = MINSYS (3.6V default) if V(BAT) < MINSYS and then regulates to slightly above the battery voltage as the battery charges from 3.6V to 4.2V.

    Regarding 4, buck converter efficiency drops as input voltage increase.  The ideal input voltage would be 8V/3.25A but you will more easily find a 9V adapter.

    Frankly, it will be a challenge to heat sink the charger at this power level.  I recommend using a charge controller like BQ24610.  It has external power FETs that are easier to heat sink.

    Regards,

    Jeff

     

  • 0 in reply to Jeff F
    Expert 2395 points

    Hello Jeff, 
                    Are you suggesting BQ24610 for BQ25895 replacement ..?

    1.We are using BQ25895 with Boost Converter TPS61088 and Fuel Gauge BQ27542-G1 for to improve performance and overcoming BQ25895 limitation is it worth it to my application ...? 

    2.Can TPS61088 help to reduces challenge to heat sink of charger and Load 

    3.we chose BQ25895 because we are looking for integrated solution of charging and we using this with our system which consist of Raspberry PI 4, GSM module, Controller(CC2652) and QCA4020 

    4.what is your suggestion for battery management system we are selected right components...?

    5.For power back-up we are going to use 5000mAh Lithium Polymer battery pack and Input adapter of system is 5.5V/5A

                   please suggest if there is anything wrong selection  

    Thanks,

    Rahul Surawase 

  • 0 in reply to Rahul Surawase48
    TI__Guru*** 143850 points

    Hi Rahul,

    Yes, BQ24610 would replace BQ25895. 

    For what purpose is the TPS61088?  Is it powered from charger SYS pin in order to provide 5V? Can you send a block diagram of your system?

    The BQ25895 is rated for 5A output assuming there is significant ground plane for heat sinking underneath the IC and the ambient temperature far below the IC max rating.  The IC automatically reduces output power if the die temp reaches 120C.  I suggest you review the thermal app note at http://www.ti.com/lit/an/spra953c/spra953c.pdf and determine whether your device can heat sink properly.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Expert 2395 points

    Hello Jeff, 
                    BQ24610/6 there is no any software control provision in the system like I2C controllable to adjust system parameter by software

    Please find the attachment for system block diagram   

    TPS61088 is used for to avoid system reset when adapter supply is off and battery takes 30mSec to supply power to system(To avoid Switch over time because of that system Reset)

    Thanks, 

    Rahul Surawase 

  • 0 in reply to Rahul Surawase48
    Expert 2395 points

    Hello Jeff,

    How I get output 5V ...? VSYS provide 5V/3A Output, if yes what is the register setting ..?

    Thanks,

    Rahul Surawase

  • 0 in reply to Rahul Surawase48
    TI__Guru*** 143850 points

    Rahul,

    The above register is read only for the ADC.  SYS will never be regulated 5V.  The charger only regulates system to MINISYS when V(BAT) is below MINSYS (REG0x03b1:3) = 3.0V-3.7V. The highest voltage SYS reaches, as the battery charges above MINSYS, is  BATREG REG0x06b2:7 = 3.840V - 4.608V plus 150mV.

    Regards,

    Jeff

  • 0 in reply to Rahul Surawase48
    TI__Guru*** 143850 points

    Rahul,

    The overall concept is valid, except, as I previously mentioned, the BQ25895 cannot provide 5 A output from 5 V input due to 3.25A max input current.  Even with only 3.25A input, my concern is still for the heat sinking of BQ25895 at max output power. 

    BQ24773 is a charger controller with external FETs that has I2C communication.   

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2395 points

    Hello Jeff, 
                     As per the Our internal Discussion We decidded to go with BQ24773 to avoid as you mention before (the BQ25895 cannot provide 5 A output from 5 V input due to 3.25A max input current.  Even with only 3.25A input, my concern is still for the heat sinking of BQ25895 at max output power.)

    BQ24773 is a charger controller with external FETs that has I2C communication, Can we need TPS61088 with BQ24773 
    We are using TPS61088 for to remove 30 ms delay from boost mode enable in BQ25895 ..?

    Thanks & Regard, 
    Rahul Surawase

  • 0 in reply to Rahul Surawase48
    TI__Mastermind 25800 points

    Hey Rahul, 

    Since you have moved on from this device and are currently evaluating the BQ24773, I will close this thread.

    Regards,

    Joel H