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BQ24650: Simultaneous Charging with USB Port Plugged In

Mezzer26
Prodigy 130 points
Part Number: BQ24650
Other Parts Discussed in Thread: BQ24076

Hey,

I am working on a small design that will have it's primary charging method be via photo voltaic cells. As a result, I have been looking through the parts catalog and found the BQ24650 which I think on the surface looks to fit my needs. However, I would like to be able to charge this design over a USB 5V line too. Will this part see a conflict if it shares charging with another charge controller if both are simultaneously in use. I.e. If the sun is shining, charging the cells, while someone also plugs in a USB cord to charge the unit, will this cause a conflict since each controller will be trying to charge the same battery pack? Thanks in advance for any help you can provide.

Best,

Mezz

  • 0
    TI__Mastermind 20570 points
    Do you have a separate charger for the USB input?
    If not, then bq24650 cannot use the USB input to charge >2s cells.
    If yes, then you will need separate control to select which input to use for charging the battery. If both source charge the battery at the same time, then the total current into the battery cannot be detected by each of the the charge controllers.
  • 0 in reply to Jing Zou
    Prodigy 130 points
    Hey Jing,
    I still have to do more part investigation but I do plan on using something similar to the BQ24076 to control the charge from the USB. Since it would seem like I fall into the second case, do you have any reccomendations for what to use to control the switching between charge controllers?

    Mezz
  • 0 in reply to Mezzer26
    TI__Mastermind 20570 points
    are you using a 1s battery or 2s? bq24076 only supports 1s battery charging.
    If you are charging 1s battery, then you can use bq24650 with USB input as well.
  • 0 in reply to Jing Zou
    Prodigy 130 points
    We are planning on either a 1s or 2s pack. I apologize, I hadn't realized what you meant with the ">2s" designator. To be explicit then, I will be using a 1s or 2s pack, and a BQ24650 can handle 1s or 2s, but no more, simultaneous solar and USB power management. Thus, I should be able to use it then?
  • 0 in reply to Mezzer26
    TI__Mastermind 20570 points
    unfortunately you will only be able to bq24650 for solar or USB when you are using 1s battery. 2s battery voltage can be up to 8.4V, with 5V USB input, you will need to use a boost charger. If you are using 1s battery, you can simply add a Or-ring at the input of the bq24650
  • 0 in reply to Jing Zou
    Prodigy 130 points

    Out of curiosity, why can't I simply connect the 5V rail of the USB Port to the Vin with the solar cell? Shouldn't the IC be able to track the voltage of the solar cell, which states cells from 5 to 28volt, and it will just read the rail as coming from the solar cell. If the solar cell goes above the 5V of the rail, then the USB will simply provide additional charge current. Is this not an acceptable method for part operation?

  • 0 in reply to Mezzer26
    TI__Mastermind 20570 points
    When the two input source has different voltage level, it is not sure how the two input source would react. USB port might see the higher voltage from the solar panel, thus USB port might get damaged.