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BQ25756: Dessign questions

Marcos Peralta
Prodigy 10 points
Part Number: BQ25756
Other Parts Discussed in Thread: , BQ25690

Hi, we are developing a product where we need to charge a 3S battery from a 12V source at 2A and, when the device is out of its charging station we need it to boost the battery voltage to 24V 1.5A to power an external load. For this we selected BQ25756 because of it's features and the ability to change charging parameters using i2C. 

As this is our first design using a bidirectional full bridge topology we have some questions regarding the design procedures given our dissimilar working conditions. 

On the datasheet a desing procedure is described for a charging application. However we couldn't find any example or application notes explaining a design validation for the reverse output or step-up functionallity. 

We understand IC's limitations regarding mosfets selection, inductor max values and working modes. Most of it's securty features will be replaced by a battery fuel gauge so we only need it to charge and boost output. 

Are there any resources that we could access to aid on our design? Sorry if this question has been asked before, we checked and did not find any.  

  • 0
    TI__Genius 9080 points

    Hi Marcos,

    We have this FAQ page about the reverse mode on the BQ2575X family of devices:

    For reverse mode, designing for the forward mode should be sufficient. Reverse mode is controlled via I2C and does not require too much additional consideration. All of the reverse mode settings are configurable by I2C. I don't think we have any application notes or reference designs about reverse mode specifically, but we have this application note about backup applications with the other versions of the device:

    This should explain the theory of how to use the reverse mode feature. Auto reverse is not a feature on the BQ25756, but by setting EN_REV=1 you can enter the reverse mode. It may also be helpful to take a look at the BQ25756EVM User's Guide for the schematic and layout images as the EVM supports bidirectionality.

    I explained the settings required for reverse mode on the device in this thread:

    I also want to mention the BQ25690 which is preview right now. It might be a better fit for the power level and easier to design as it is integrated FET.

    If you have any further specific questions about how to use reverse mode, I can help provide guidance as well.

    Best regards,
    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 10 points

    Hi Michael, thanks for your quick answer! I highly appreciate it. I will study all the material you provided and start our design. If i have any other questions about this design is it ok to continue this thread or should I start a new one?

    About the BQ25690 yes I saw it and I think it would be a great alternative for our use case, however we are in a little hurry as our client need this product for february next year. We will have it in our radar for when it officialy launches to see if we can transition to it.

    Just out of curiosity, is it possible to aquire some BQ25690 and send them directly to an assembly factory like JLCPCB (or any other)? I saw it is out of stock and the MOQ is 1K devices which we don't need right now.

    Thank you!
    Marcos

  • 0 in reply to Marcos Peralta
    TI__Genius 9080 points

    Hi Marcos,

    Marcos Peralta said:
    If i have any other questions about this design is it ok to continue this thread or should I start a new one?

    Either one will work. The threads get automatically locked after a certain amount of time though. I don't know how long that is though.

    Marcos Peralta said:
    Just out of curiosity, is it possible to aquire some BQ25690 and send them directly to an assembly factory like JLCPCB (or any other)? I saw it is out of stock and the MOQ is 1K devices which we don't need right now.

    I don't think that will be possible right now. It just launched last week so we don't have much in stock. It's pretty much produced to order this early on I believe.

    Best regards,
    Michael