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BQ24773: Design confirmation

Srinivas Beera
Prodigy 220 points
Part Number: BQ24773
Other Parts Discussed in Thread: BQ27542-G1, BQ25703A

Hello, 

As per our requirement , we have chosen below TI ICs (charger + Gas gauge). Please give your comments on "whether the components match to requirement". So that we will procure evaluation boards.

Our requirement :- 

Adapter voltage   -   (10 -20)V    or USB type -C (12V/3A  or 15V/3A or 20V/3A)

Battery configuration - 3S1P 

Battery voltage and current - 11.1V/3000mAh

System continuous current - 2A  , System pulse current - 4.7A for 4 sec duration. 

selected IC:- 

Bq24773 - I2C , nvdc charger 

bq27542-G1 - Gas gauge (JEITA compatible)

NVDC charger has chosen because we have option of using USB type-C (12V/3A  or 15V/3A or 20V/3A) instead of AC adapter. When 12V/3A type-c source used , System current = Type-c adapter current + battery current .

Example - System pulse current is 4.7A for 4 sec  , Type-C adapter (12V/3A) wont able to give system total current , it can draw extra current from battery. 

System block diagram attached , Please give your comments. 

  • 0
    TI__Mastermind 20570 points

    Is 11.1V the maximum charge voltage? What battery chemistry are you using.

    Typically for Li-ion batteries, it is 4.2V/cell. 3S1P configuration will have 12.6V as maximum battery charge voltage. 

    For 12V input voltage with bq24773, it cannot charge up the battery voltage to 12.6V.

  • 0 in reply to Jing Zou
    Prodigy 220 points
    We are using li-ion batteries. You are right , for 12V/3A type-c source is not useful in our application. I just gone through USB Type-C , new standard suggest normalize voltages are 5,9,15,20V/3A. So we need to go with 15V/3A or 20V/3A.

    If we are going with 15/3A or 20V/3A , then there wont be any issues in above design right?????????????
  • 0 in reply to Srinivas Beera
    Prodigy 220 points
    Also give your comments for using any Filter (LC) in above design for noise suppression.

    Charger swithcing frequency - 600kHz
    12V Boost converter switching frequency - 600kHz
    5V Buck converter swithcing frequnecy - 600kHz
    3.7V buck converter switching frequency - 340kHz

    If we are taking care in layout (layout recommnedation as per charger IC , gas gauge , converters datasheets) of above design , still input filters like LC required?
  • 0 in reply to Srinivas Beera
    TI__Mastermind 20570 points
    Regarding on "If we are going with 15/3A or 20V/3A , then there wont be any issues in above design right", yes.
    Regarding on input filter design, please refer to the datasheet Input Filter Design section for detail explanation.

    What is your schedule looks like? We do have a new device that works with full range of type C voltages releasing end of next month. If this meets your project schedule and you are interested, please contact your local TI sales team to request more info.
  • 0 in reply to Jing Zou
    Prodigy 220 points
    We have some time to wait , now we are in evaluation mode. I have final doubt on above design.

    Charger - Power dissipation
    Vin - 15V
    Vout - 11.1V
    Iout - 4.235A,
    Iin - 3A
    Eff - 90%
    Rthja - 33.3
    PD = (15*3)-(11.1*3.64) = 4.6 W
    Tj = (4.6* 33.3)+25 (Ta)
    = 178C

    It is more than actual junction tempertaure , Is my calculation wrong ?
  • 0 in reply to Srinivas Beera
    TI__Mastermind 20570 points

    the bq24773 is an charge controller with external FETs. The power loss is mainly on the switching FETS where the high current goes through. The high current path does not go through the bq24773.

  • 0 in reply to Jing Zou
    Prodigy 220 points
    Hello Jing Zou,

    I have a question on thermal point of view. For example gas gauge is not monitoring proper battery temperature , Battery temperature is above specification . Charger will continue to charge the battery ............ How it will be protected ?
  • 0 in reply to Srinivas Beera
    TI__Mastermind 20570 points

    Again the bq24773 is a host controlled slave. All of our host controlled charger does not have a independent battery pack temperature monitoring to suspend the charging when the pack temperature is outside of the window. Host controlled charger relies on the host to monitor the battery pack temperature and write command to the charger to suspend charge.

  • 0 in reply to Jing Zou
    TI__Mastermind 20570 points
    I am referring to multicell host controlled charger does not have TS monitoring function.
  • 0 in reply to Jing Zou
    Prodigy 220 points
    Hello Jing,

    I have just seen new charger IC from Texas (BQ25703A). If I will use USB type-C source for charging the battery by using BQ25703A, No need to use Type-C PD controller for negotiation power levels.

    Thanks
    Srinivas