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Original question:

LI-Ion Battery Charger

BQ24133: BQ24133: How to increase battery charging current

Udayakumar R
Prodigy 80 points
Part Number: BQ24133

We have made battery sharing circuit /PCB using BQ24133. it  primary functionality looks ok. The Li-on battery is getting charged . But it takes 8-9 hours for full charge. it is consuming  only 300mA.. Can anyone help me how to increase the battery charging current ( our expected charging time for full charge is 3-4 hrs). 

the measured values are

voltage at ACSET pin is 0.807V

ISET voltage is 0.404V

As per design,

Input ACSET voltage is 2A

I charge  is 1 A

Thanks in advance for your reply.

  • 0
    TI__Guru*** 143910 points
    Hi Udayakumar,

    Do you have a load on SYS output (i.e. directly pulling current for load from the input power source)? Can you double check your values for the current setting and current sensing resistor using the design spreadsheet at the link below:

    www.ti.com/.../sluc244

    What is the voltage at SRN pin?

    Regards,
    Jeff
  • 0 in reply to Jeff F
    TI__Guru*** 143910 points
    Hi Udayakumar,

    Any update on this?

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 80 points

    Dear Jeff,

    Thanks for the follow up.

    It was tested with 3 Li-ion batteries.

    The SRN values were unique for each batteries.

    Let me name the Battery 1, 2 and 3.

    Voltage at SRN is 7.1 for Battery -1

    Voltage at SRN is 7.7 for Battery -2

    Voltage at SRN is 8.3 for Battery -3

    But , The current consumption is almost same i.e., 300mA

    The input voltage is 12V thru  Bench power supply .

    Based on the spreadsheet shared in the last message, the cap value at TTC is changed to 22nF from 100nF.

    Note: Temperature sensor is not used . Hence , TS is pulled down with 10K resistor. in addition to  R8 and R9 as per your spreadsheet for BQ24133.

    Please share your comments to increase the charging current?

  • 0 in reply to Udayakumar R
    TI__Guru*** 143910 points
    Hi Udayakumar,

    Given the SRN voltages, the charger is not reducing the current due to entering constant voltage (CV) mode. The charge current is regulated based on the voltage difference between the SRN and SRP resistors, in other words the voltage across the sense resistor. What is the voltage across the sense resistor? The only other control loop that could reduce the charge current is the input current regulation loop. That loops senses the voltage across the ACN resistor and only allows that amount of current to flow directly to the system, with the remainder available to the buck converter for charging the battery. What is the system load current? Is it stealing away the current to the buck converter for battery charging?

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 80 points
    Dear Jeff,
    Here is a details of voltage at sense resistors.
    Voltage across at Rsr = 0.003V; with reference to GND 7.33V and Voltage across at Rac = 0.006V for Battery 1
    Voltage across at Rsr = 0.002V ; with reference to GND 7.61V and Voltage across at Rac = 0.006V for Battery 2

    the system voltage is connected to LDO- 5V but there is no load across output of LDO - this scenario maintained for the testing purpose.

    The bench power supply setting is 12V /3A.

    I would like to know that , Any one of your customers has used BQ24133 and they achieved charging current is > 300mA? or is there any internal lab report ( TI) available where BQ24133 is tested for 1A charging current?

    Regards,
    Udaya