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BQ25703A: bq703a charge

Belhaj ltaief Samir
Intellectual 380 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQ25703
Can you give me the operating principle of BQ25703A.
how is the loading of battery in parallel with the system
how the battery gives the system when the power is removed
  • 0
    TI__Genius 16185 points

    Hi

    BQ25703A is TI buck-boost charger solution, I attached file for your understanding how it works. This part can support 5V~20V input and 1~4cell battery number. Please forget different part number, They ate the same with different communication interface, one is I2C, the other is SMBUS.

    In this topology, there is BATFET to separate system and battery power, so if adaptor plug out, then this BATEFT will be turn on to supply battery power to system.

    Thanks

    Buck_Boost Transition 25700A_01172017.pdf

  • 0 in reply to Paul Yeh
    Intellectual 380 points


    first case: the power supply is not removed How the charger powers the system and charges the battery.

    second case: when the power is removed How does the battery power the system

  • 0 in reply to Belhaj ltaief Samir
    TI__Expert 5330 points

    first case:  the power supply is not removed.  How does the charger power the system and charge the battery?

    In this scenario, assuming the battery voltage as above the MinSystemVoltage set in registers 0x0C/0x0D, the BATFET will be enabled so that current from the switching regulator flows both into SYS and into the Battery, powering the system and charging the battery.  In constant current charging mode, the voltage of SYS will be approximately the battery charging current * R_DSON of the BATFET above the battery voltage.  As SYS pulls more or less current, the feedback loop will adjust accordingly so that the total current through the switching regulator is ISYS+IBATT. 

    second case: when the power is removed, how does the battery power the system?

    The BQ25703 will also turn the BATFET on in this scenario, providing the minimum resistance path from battery to SYS and the battery will provide power to SYS.  In this case, the voltage on SYS will be slightly below the battery voltage according to system current * R_DSON of the BATFET. 

    Further detail is available in datasheet section 8.4 "Device Functional Modes," particularly section 8.4.1.1 "System Voltage Regulation with Narrow Voltage DC Architecture" and section 8.4.1.2 "Battery Charging" in addition to the resources provided by Paul in his earlier post.  I would also recommend that you order the EVM.  The EVM user's guide has a nice walk through with instructions for demonstrating these modes in a test setup.

    Regards,

    Steve