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BQ25100: Charge current at <10mA possible?

Franz Schellhase
Expert 3605 points
Part Number: BQ25100
Other Parts Discussed in Thread: BQ25155

Hi team,

My customer has a couple of questions about the BQ2510x series. Can you help them out?

  1. Charging current
    1. At the beginning of the data sheet it is described that the charge controller supports a charging current of 10 mA - 250mA. How is this to be understood in connection with the charge termination current of 1mA?
    2. Could the charge controller also charge a battery with a lower current?
Parallel connection of battery and system
  1. The data sheet describes that the system, which is normally supplied by the battery, is also supplied by the output when it is charged. How can the charge controller draw conclusions about the accumulator here? How does the controller recognize when the battery is full?
  2. Could you also include the BQ25155 in this context? Why is the system supplied via PMID during the charging process with BQ25155?
  3. How can the system be powered when the charge controller charges the battery with CV & CC?
  4. How high can the maximum consumption of the system be?
Temperature sensor
  1. What are the effects on the charge controller/charging process if the battery temperature sensor is missing?

Thank you,

Franz

  • 0
    TI__Guru* 75676 points

    Hello Franz

    Slightly lower charge currents are possible, but termination current below 1mA is challenging.

    How low a charge and termination current do you require for you system?

    "The data sheet describes that the system, which is normally supplied by the battery, is also supplied by the output when it is charged. How can the charge controller draw conclusions about the accumulator here? How does the controller recognize when the battery is full?"  --- This is a common problem for a non power path system.  The battery charger will supply a fixed amount of current to the output during the CC mode.  The design needs to take system load into account so that enough current is available to support the charge.  Also when the system enters CV mode it will require that current decreases low enough to terminate.  Too much system load will present problems.

    The BQ25155 is a very different design and needs to be addressed in a separate post.

    If the TS pin is open unit will enter TTDM mode which is similar to power supply mode.  See TTDM section of data sheet 8.4.5

  • 0 in reply to Bill Johns
    TI__Expert 3605 points

    Hi Bill,

    Thank you for your insights! I have a couple follow-up questions to fully grasp your answers. I will ask about BQ25155 in a separate post.

    1. Charge current
      • This question was aimed at the fast charge current, which is rated at 10 - 250mA, rather than termination current. Is it possible to set fast charge current to a value below 10mA, possibly down to 1mA? 
    2. Parallel connection of battery and system
      • How would you go about finding maximum system load without causing problems?
    3. Temperature sensor
      • If I understand correctly section 8.4.5 describes what happens when TS goes high during a charge cycle. What happens when the battery is fully charged afterwards and TS stays high? So if the customer doesn't use a temperature sensor. Will it work normally?

    Best regards,

    Franz

  • 0 in reply to Franz Schellhase
    TI__Guru* 75676 points

    Hi Franz

    1.) Charge Current -- Termination is a percentage of the fast charge current, when reducing the fast charge below 10mA adjust termination to keep it above 1mA ( 8ma fast charge and 12.5%).  But accuracy decreases at lower current, it is +/- about 5%.

    2.) Parallel Connection -- If the system load is greater than termination current (1mA) charger will not terminate charge and set a safety timer fault (10hr ).  The system current can be measured or calculated. 

    3.) Temperature Sensor -- In TTDM mode the when fully charge the charger voltage is still applied to battery.  Typically the charge profile will remove voltage from battery after charge is complete.  Check with battery manufacture if this is acceptable.