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BQ24617: System, Charge-Current, Li-Ion/Li-Polymer ?

Paul K52
Intellectual 640 points
Part Number: BQ24617

Hello,

im having 3 questions about this chip

1.

in the datasheet it is written, that this chip can Charge a battery with a Maximum current of 10 A. I thought, that this current Comes from the Adapter. But, as I saw from the datasheet  on page 7 it says:

The Adapter supply current is, depending on the test condition, typically 1 mA to 25 mA.

2. Refering on page 26 of the datasheet, I see the "System" on the right side. What exactly is the "System" about?

3. A few datasheet like this one (BQ24617) ensure that this chip will work with Lithium Polymer Batterys and Lithium Ion Batterys. There are also IC's which say, that they can only work with 

Lithium Ion batterys.

So, does it really matter to care about, whether the IC can Support Lithium Polymer batterys? Or , is it okay, if the datasheet says that the charger can Support Lithium Ion batterys?

When you click on the link you see, that Lithium-Ion and Lithium-Polymer are put together in one menu Option.

www.ti.com/.../products.html Buck;Switch-Mode Buck-boost&p1341=I2C

Thanks for helping.

  • 0
    TI__Mastermind 20570 points

    Regarding 1, the supply current means current goes into the IC pins (VCC, ACP, ACN), it does not mean the charge current. The charge current is going to be supplied by the adapter.

    Regarding 2, System means you can connect a system load to this node. The bq2461x features Dynamic Power Management (DPM) which reduces battery charge current when the input power limit is reached to avoid overloading the AC adapter when supplying current to the system and the battery charger simultaneously.

    Regarding 3, typically li-ion and li-ion polymer batteries has the same charge profile, so as long as the charge profile of the charge matches the battery, you can use the charger. 

  • 0 in reply to Jing Zou
    Intellectual 640 points
    Regarding 2: Could you get in greater detail?

    So the DC charge current comes from the adapter. When I want to charge the battery, this current will flow through the Q1(ACFET), the second P-Channel FET, the RAC-Resistor and finally from the Q4 FET to the PACK+ pin, where the battery is connected to.
    I think this is correct, right? (Refering to Figure 19, page 26)

    Now I see, that the battery is getting full. The charge current has to be reduced. This is done by the Dynamical Power Manangment. The Dynamical Power Managment refers to the Q4 and Q5 FET. If the charge current into the battery has to be reduced, Q4 and Q5 are switched off and on with a high frequency from the HIDRV and LODRV Pins of the chip. In this case the charging current is getting lower and the system current is getting higher. The system current can then flow into my load, without effecting the battery, because the BATFET is offline.

    Just to make thinks clear: When im charging I have the option to run my load, continously( Battery in use or in charge) doesnt matter, right?
    The load could be my motor, a simple resistor or something else...?

    Is the way Im thinking correctly?

    Thank you for helping me, to figure this out.
  • 0 in reply to Paul K52
    TI__Mastermind 20570 points
    Referring to figure 19, Q1 and Q2 is the ACFET and reverse current blocking FET. Q4 and Q5 is the highside and low side switching FET. Q3 is the battery-to-system load BAT PMOS power FET to isolate the system from the battery to prevent current flow from the system to the battery, while allowing a low-impedance path from battery to system.
    Battery charging profile is not done by the dynamic power management. When the battery is getting full and entering CV mode, the current tapers . It is done by internal regulation. The dynamic power management is basically done through the control of Q3 in this part. The dynamic power management is for supplying the system load. Basically when Padapter < Pbattery_charge + Psystem, the IC will reduce charge current so that system load has higher priority.
    Yes, you can run your load regardless if the battery is in use or in charge from the system connection node in figure 19.
  • 0 in reply to Jing Zou
    Intellectual 640 points

    "The dynamical power managment is  basically done through the control of Q3 in this part".

    As you said, the dynamical power managment is for supplying the system load. When the battery is full, the chip will reduce the charge current.

    With the information on page 14, the datasheet says:

    "The bq2461x features Dynamic Power Managment which reduces battery charge current when the input power limit is reached to avoid overloading the AC adapter when supplying current to the system and the battery charger simultaniously".

    That means: If I want to charge the battery with a charge current and I want to run my load with a system current simultaniously, this both currents together could be to much for the adapter: There is a maximum current, which the adapter can provide. Now, here comes the DPM:

    Lets assume, that the total current from the adapter is a constant current. We have programmed a current threshold, which can't be exceeded during charging (It's always the same current) ( Itotal=const=Icharge+Isys)

    Now the IC's is detecting, that the system load wants to have more current. So theoretically the total current is also getting higher (Itotal<Icharge+Isys). And then, the total current threshold is exceeded.

    So the charge current has to be reduced to ensure that Itotal is always the same.

    Is this explanation correct?

  • 0 in reply to Paul K52
    TI__Mastermind 20570 points

    "As you said, the dynamical power managment is for supplying the system load. When the battery is full, the chip will reduce the charge current."

    My point is  even when the battery is not full, the charger will reduce charge current. 

    The rest of your understanding is correct.

  • 0 in reply to Jing Zou
    Intellectual 640 points
    Ah okay. So this means: If the system load will require more current and the battery is still charging, the battery will get less current, because the system load has priority-> So the system load will get more current.

    Okay I see. But when I only want to charge the battery and I do not want to supply current to the system load during charging, DPM is not nessecary for me, because I will prevent current flow to the system load.
    Refering to figure 19, on page 26, I would put a diode, between the connection of C8 and C9. This diode can only let current flow from the right to the left. Would this be enough to prevent current flow from the adapter to the system?
  • 0 in reply to Paul K52
    TI__Mastermind 20570 points
    You do not need to connect to the system if you do not have one. You can simply ignore the system arrow. Do not recommend to add a diode in between C8 and C9 as efficiency might suffer.