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BQ24054 design review

david sun77114
Expert 2130 points
Other Parts Discussed in Thread: BQ24050

Hi, 

this is my first time use BQ24050, charging current is small because the batter capacity is small, 10mA based on my calculation, will this design work. if the VIN connect to load regulator, it will keep on during the charging. once charging complete. based on the current of this load, for example, 1mA on average. will BQ24050 keep output current, or it will shut down based on the battery is full. 

Thanks,

David Sun

  • 0
    TI__Mastermind 19430 points
    Not sure if I understand your question. Are you asking if the load can be powered by the input source after charge is terminated?

    Once the battery charging is terminated, the IC stops to output current to OUT pin and the load will then be powered from the battery.

    While the battery is charging, the output current is shared by the battery and the load. Since this is not a power path charger, the IC cannot differentiate the current goes into the battery from the current goes in to the load. If your load is constant at 1mA, then when setting up the termination current, you should add in the additional 1mA from the load. For example, if the charging needs to be terminate at 1mA and you have 1mA load on as well, then you should set the termination current threshold to 2mA.

    I notice you have the ISET resistor set at 520k ohm which is outside of the datasheet spec. The minimum charge current can be set at 10mA by RISET = 52.3k-ohm. We do not warrant any operation outside of the datasheet spec.
  • 0 in reply to Jing Zou
    Expert 2130 points
    I don't know why I couldn't get email acknowledge from this forum. I have to login to check the answer. thank you very much for answering my question. for above schematic.
    R5 is 47K, and voltage is 1.68V I don't think the current draw from Vin is higher than 10mA, but I haven't measured it yet. (have to remove some component to do it).
    seems to me there is a conflict in the data sheet.

    on page 3, pin definition Riset and current follow this range
    Programs the Fast-charge current setting. External resistor from ISET to VSS defines fast
    ISET 2 2 I
    charge current value. Range is 52.3k (10 mA) to 540 Ω (1.0 A).


    on page 5. last line

    I Programmed Output “fast charge” VOUT(REG) > VOUT > VLOWV, VIN = 5V, ISET2=Lo,
    OUT(RANGE) current range RISET = 675 to 10.8kΩ 10 800 mA


    in my case if the statement on page 5 is correct, should I change the Riset to 10.8Kohm. to set the current limit to 10mA.

    thanks
  • 0 in reply to david sun77114
    TI__Mastermind 19430 points
    IOUT is calcuated as KISET/RISET. For 10mA, KISET = 520. Thus to RISET should be 52k Ohm. Test condition on page 5 will be updated.
  • 0 in reply to Jing Zou
    Expert 2130 points
    Any suggestion why I see 1.68v on the out put, I measured corrent by set the voltage to 3.7v, is around 5mA.
  • 0 in reply to david sun77114
    TI__Mastermind 19430 points
    I am not able to understand your design requirements. Are you trying to set charge current to 10mA?

    If you are not using the D+/D- lines, please short thise two pins. Just note that if D+/D- detection is not a requirement for your design, please have a look at ba24040 instead.

    Is there any load connecting at OUT pin?

    What is 1.68V measured at? what is 3.7V measured at?

    How are you measuring the current?

    Can you show scope capture on VIN, IIN, VOUT, IOUT?

    I also highly recommend to evaluate on an EVM before doing your own boards.
  • 0 in reply to Jing Zou
    Expert 2130 points
    Do you mean short D+,D-together or short them to ground,
  • 0 in reply to Jing Zou
    Expert 2130 points
    Here is my test
    1. Without battery, BT1, the output voltage is 1.68v, I dont know the current at this moment.
    2. Remove the USB input, attatch BT1(3.7v) to the board, the current from this battery, is 5mA.
    So, I got the conclusion, that the load will draw 5mA from 3.7v power.
    I will catch the waveform and send to you later,
    Thank you for your prompt reply.
    David
  • 0 in reply to david sun77114
    TI__Mastermind 19430 points
    Please see datasheet page 16 to 17 on the operation on D+/D- detection. Short D+ to D-.

    Can you disconnect the load and measure the voltage at OUT pin as well? The bypass cap should be placed as close to the OUT pin as possible.