Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 54 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

BQ25798: 20 multiple single cell battery chargers in parallel via USB-PD

Muhammad Awais
Intellectual 640 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ25758S, BQ25758, TPS25751

Tool/software:

Hi TI Team,

We are designing 20 single cell Li-Ion battery chargers with 0.5A max charging current. Please note that these 20 charging outputs will be deployed so that we can charger either single device or multiple up to 20 at the same time. The input is suppose to be via USB-PD charger output.

Right now I am looking at charging ICs like BQ25798RQMR to accept voltage across USB-C PD (5V to 20V) but as we need 20 of these BQ25798RQMR so I am not sure if we can put 20 of these in parallel and control via PD controller. Please confirm? Secondly this solution will be very expensive as do need 20 charging outputs but each one is just single cell with only 0.5A charging current. 

Another solution is to add a buck-boost regulator to accept USB-C PD (5V to 20V) to generate a 5V output but in this case we need a 10A (20x0.5A) = 10A. If you suggest going this way then can you please share any regulator options that we can use for 5V, 10A and accept any PD input, or if not possible then two 5V, 5A but input via USB-C PD?

Kind regards,

Muhammad Awais 

  • 0
    TI__Intellectual 1710 points

    Hi Muhammed,

    One factor to consider when putting these devices in parallel is adjusting the registers with I2C.  The charger ICs only have one I2C address, so you will either have to control all 20 chargers at the same time with one MCU or you will have to get 20 MCUs to control each individual charger IC.  

    Another possible situation to consider is the thermals of BQ25798 with a 20V Vin, 4.2V Vout and 0.5A Ichg.  Each charger will have some amount of power dissipation, and the PCB could get hot with 20 of these ICs

    Using our BQ25758S DC/DC converter to regulate to ~5V will help minimize the thermals.

    Besides handling the I2C transactions and, I do not see any other obvious concerns as long as each charger IC charges only 1 pack.  

    Regards,

    Charles Harthan

  • 0 in reply to Charles Harthan
    Intellectual 640 points

    Hi Charles,

    I like your idea of using BQ25758S as a 5V output but please help me to understand this chip before going with it please help me to answer these questions so that we may proceed accordingly. 

    1. Can you please confirm that we may use BQ25758S only as a buck-boost regulator with 5V output and then adding multiple single cell battery chargers? Please note that we will be using simple 5V input and single cell chargers that doesn't need any I2C to program as it will be hectic to deal with 20 chargers to be programmed via I2C. So this BQ25758S will be a 5V source only. I can see this chip is a Buck-Boost converter with Charger features as well so this is confusing me. 

    2. I have a quick look on this BQ25758S datasheet stating that the default output is 5V. Can you please confirm that we can safely use it to generate a 5V, 10A output? As per the datasheet equation (4) is showing how to set the max current limit. I am assuming that if we will use the 5mOhm then we may set the max current output limit to 10A. Please confirm?

    3. Any recommendation for the PD chip to use along with BQ25758S. As you know our application is USB PD sink only. 

    4. BQ25758S is not where available. Can you please confirm on its availability and time. I can see BQ25758 that is in stock that has even wider input range and I believe both are pin compatible. 

    Kind regards,

    Muhammad Awais

  • 0 in reply to Muhammad Awais
    Intellectual 640 points

    Hi Charles,

    Kindly let me know your input on above questions so that we may move forward. 

    Thanks and regards,

    Muhammad Awais

  • 0 in reply to Muhammad Awais
    TI__Intellectual 1710 points

    Hi Muhammad, 

    Apologies for the delay. About your questions:

    1. BQ25758S is a buck-boost controller only. It does not have any battery charging capabilities.  

    2.  Yes you a can use a 5mOhm.  The default output current is 20A, and use can use the Iout pin to set 10A.  The IC will choose the min between the register value and the Iout pin which will be 10A in this case.  See page 32 of the datasheet.

    3. You can use TPS25751

    4. Yes, we have inventory of BQ25758S. BQ25758 is P2P replaceable too and is a higher power option.

    Regards,

    Charles Harthan