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BQ25713: BQ25713 - IS this the right part? help selecting other parts for a complete wireless 3cell Li-Polymer charger for wheeled robotics

Adam Donovan
Prodigy 120 points
Part Number: BQ25713
Other Parts Discussed in Thread: BQ24773, DRV8313, BQ25882, BQ40Z50, BQ24133, BQ24770, LM51501-Q1, BQ5101

Background -

I work on swarms of wheeled robots(hundreds).  Im sick of plugging them all in when they run out of charge so Im starting to design a wireless 5v charger for a 3cell battery. (rc unprotected ) 

Question in detail -

I need a simple as possible I2c solution to control the charge, balancing and measuring(fuel gauge)  of a 3 cell battery and ideally 15watt fast charging.  The robot has I2c and other pins if necessary but low power and low device count would be fantastic.

I have not had much luck on finding an example circuit that has all these features

  • 0
    TI__Expert 5330 points
    Hi Adam,

    The BQ25713 will definitely work in your application, although, depending on your input voltage it may be more fully featured than you require. The BQ25713 is able to seamlessly transition between buck and boost modes. You mentioned 15 Watt fast charging in your post. I don't know if this is will be coming into our device as, for instance, 5V@3A or 15V@1A, but depending on your input voltage requirements, you may not need the ability to both buck and boost.

    If you are able to design the wireless transfer stage to generate a high enough voltage input to the charger, i.e. 15V+, then you could use a buck-only regulator to charge. This would be a simpler and smaller solution. If so, we have a wide range of products that fit this space. You might want to look at the BQ24735A and the BQ24773.

    But if you need to support a range of input voltages that may be either above or below your battery voltage, then I think that you have the best device with the BQ25713.

    Regards,
    Steve
  • 0 in reply to Steve Preissig
    Prodigy 120 points

    Thanks Steve,

                           I would need some additional help if I am to proceed to design something if possible.  Firstly  the data sheet doesn't really provide to me information on how cell balancing is achieved. Im used to seeing  3 wires for example a 2 cell lifepo4 or lipo.  I dont get how a 2 wire connection can determine if a multiple cell is in balance or not?

    Also for simplicity I want to use off the shelf inductive charging devices that are used for phones.  I dont really want to design anything beyond the 5v 1amp input coming from the inductive charger if at all possible so I can live with the additional time it would take to charge over the cost of designing my own inductive chargers.  

    Id be happy to go with something simpler if you think that there is say an IC that can handle take 5v to charge 2 cells @8.4v then I can boost it up from there to say 10-12v.  I have been doing this with a buck step up from one cell(3.3-4.2) but things get a little toasty and had to tune down to 8.4volts which isnt ideal for the DRV8313s that drive the robots BLDCs wheels.(The DRV8313 is great otherwise though).

    Have a look at the project page and you can see what we are doing, be great to have a little more help:)

    http://hochschuh-donovan.com/portfolio/empathy-swarm/ 

  • 0 in reply to Adam Donovan
    TI__Expert 5330 points
    Hi Adam,

    We do have a product (BQ25882) designed for boost-only two-cell operation. While this is probably a simpler solution for a 5V to 2-cell configuration, I don't think that the overall solution is going to be simpler in your application -- i.e. I think that using BQ25713 and boosting up to support 3 cell would be an overall simpler, smaller and more efficient solution than using BQ25882 with two cells and then having a secondary solution to boost the two cells up to your system's operational voltage. Still, I wanted to let you know about the BQ25882 so that you can make your own decision.

    Given the information that you have provided, I do think that the BQ25713 is the best fit for your application. You are correct that this device does not have integrated cell balancing. We recommend that cell balancing is handled directly at the pack using a pack manager IC such as the BQ40Z50. This part, as well as our other pack manager ICs, are supported by our battery gauging group. Please post a question on the gauging forum to get more detail on TI's recommendations for cell balancing.

    Regards,
    Steve
  • 0 in reply to Steve Preissig
    Prodigy 120 points

    Thanks Steve Im slowly getting a better overview bear with me.  Just going back to your original idea of designing the +15 inductive transfer I am wondering what suitable components might fit there.  Its not completely obvious how to filter components in the charger category for inductive receivers @ 15v

  • 0 in reply to Adam Donovan
    TI__Expert 5330 points
    Hi Adam,

    The BQ24133 is Buck architecture with integrated FETs. It is a little different from BQ25713 in that it uses the power path architecture where system runs off of adapter voltage (or inductive receiver voltage in your case) and the buck is used to buck this voltage down to charge the battery. This is as opposed to NVDC architecture of BQ25713 where the adapter voltage is first bucked down to a value just slightly over the charging voltage and this is what is passed to the system. (In the case that the battery is highly depleted, there is a minimum system voltage that can be set.)

    The BQ24770 is an NVDC controller (external FETs for switching regulator.) It is similar to the BQ25713 you are already looking at, except that it can only buck the input voltage down to charge the battery, whereas BQ25713 has buck/boost operation with seamless transition.

    Regards,
    Steve
  • 0 in reply to Steve Preissig
    Prodigy 120 points
    Actually I think that perhaps staying with single cell and then boosting up is going to be the most simple. I have been look at the LM51501-Q1 at someting that might handle enough current (2.5-4.2v input) to (10 volt output) Im already using a charger from TI that does an ok job at getting voltage to charge the battery bq5101(ill try the bq5105 at some point). But now help with finding a boost converter that not going to melt running at 1-2amps for a few mins at a time
  • 0 in reply to Adam Donovan
    TI__Expert 5330 points
    Hi Adam,

    Please start a new thread with LM51501 part number. The boost controllers are handled by a different group at TI, and I think you will get the best direction by starting a separate discussion with that team. Let me know of any other questions regarding the battery charger portion of the design.

    Regards,
    Steve