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BQ24170 problem

Chee Ho Kar96
Prodigy 90 points
Other Parts Discussed in Thread: BQ24170, BQ24172

Hi TI,

I am using BQ24170 to design a circuit which use 13.5V-15V DC input to charge 3Cells LI-PO battery.

Refer to the data sheet description, it said the system load path can be directly connected to battery in "1 Cell application".

My questions:

1. For 3Cells LI-PO battery, is 13.5V the min supply voltage to the IC?

2. Can the system load path be directly connected to battery in "3 Cells application"? Or I only can use automatic power path selector solution in "3 Cells application"?

Many thanks.

  • 0
    TI__Expert 3160 points

    Hi,

    1.  What is your voltage per cell?  The bq24170 only supports 4.2V/cell, but you can use the bq24172 if you would like an adjustable cell voltage such as for Li-Po battery. With 4.2V/cell 13.5V is the lowest recommended input voltage, but if you have a lower cell voltage than the input voltage can be lower. 

    2. You can connect the system load directly to the battery such as shown in the 1 Cell application, but there are some limitations to this configuration and in most cases it's preferable to use the traditional configuration. 

    Thanks,

    Rachel

  • 0 in reply to Rachel Moore
    Prodigy 90 points

    Hi,

    Thanks for the answer. But I have some question about question 2.

    You mention bq24170 can connect system load directly to the battery, but what is the limitations? (system current?)

     

    Now my design is 15V DC in, and battery is 3cells 11.1V Li-po, I don't want two different voltage go in the system (audio amp), hope to use only battery for power supply.

    If I connect system load path directly to battery path, the IC will charge the battery  and the battery provide power to system at the same time?

    Many thanks.

  • 0 in reply to Chee Ho Kar96
    TI__Expert 3160 points

    If you want to charge 3.7V/cell battery, you will need to use the BQ24172 to set an adjustable cell voltage.

    If you connect the system to the battery, the BQ24172 will charge the battery and provide the system power but the potential limitations are:

    • The system will always have the same voltage as the battery regardless of state of charge.  If the battery is too low the system may not be able to start up until the battery is charge up more. (no instant on)
    • Charge termination will need to be disabled because if charge is terminated the converter will shut down and not supply power to the system
    • When the system is connected after the sense resistor, the fast charge current (ISET) will limit the ISYS + IBAT total current.  When ISYS = 0A, the total charge current must still be an acceptable charge rate for the battery. 

    I'm not sure I understand your concern regarding the different input voltages between VIN and VBAT.  Even with the system connected to the battery, it will still experience a range of voltage equal the full and depleted voltage of the battery. I believe the better solution is probably to consider an additional power stage (buck and/or boost regulator) to provide your system with a stable input voltage. 

    Thanks,

    Rachel