• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 110 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

BQ29209: Overvoltage protection

BQ25798: BQ25798 paired with BQ29209

Brian Stull
Prodigy 30 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ29209, , TPS25751, INA219

I'm in the very early stages of a design and I'd like some feedback on my overall concept and to see if there are any things I'm missing or other parts that would be better for my needs. 

I'm designing a board that will basically just consist of a microcontroller and application specific hardware paired with a battery backup/charger in order to allow operation off either powered (USB C or 9VDC) or battery. 

A very basic block diagram is attached below. 

The batteries will be two 18650 batteries @ ~3.7V each. I need to charge them and operate off USB or 9VDC and then automatically switch over to batteries when input power is disconnected. 

I'm thinking of using a BQ25798 battery charger with a BQ29209 for voltage protection and cell balancing (not sure if this is reuired). It looks like this combination would do what I need for charging and protection. Would you have any circuit examples or app notes that would help with what I'm trying to do? It seems like a very common use case these days. 

I'd be happy to post my complete schematic for review later but at this point I'm just looking to make sure the direction I'm going makes sense. 

I appreciate your help!

 

image.png

  • 0
    TI__Guru**** 170086 points

    Hi Brian,

    The block diagram looks reasonable.  I am not aware of any app notes or reference designs using the BQ25798 with BQ29209.  What is the purpose of the INA219?  Also, there is a reference design of BQ25798 with TPS25751 USB-C PD controller if you are using PD.  https://www.ti.com/tool/USB-PD-CHG-EVM-01  The BQ25798 cannot negotiate directly with USB-C ports.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 30 points

    Thanks, Jeff.

    The INA219 is for battery monitoring. The existing design has that IC and the firmware is already written for that piece of hardware. I want to keep the firmware unchanged from the previous design so I would be running the BQ25798 without communicating to the IC. Also, I hadn't planned on using the BQ25798 to negotiate to the USB-C port... is that just for higher power charging capability?

  • 0 in reply to Brian Stull
    TI__Guru**** 170086 points

    Hi Brian,

    If you only using USB-C at 5V, then the only concern is ensuring that the BQ25798 input current limit is clamped by ILIM_HIZ resistor to slightly below the USB-C max output current.  Otherwise the charger could collapse the USB-C port by pulling too much current.

    Regards,

    Jeff