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BQ24259: Tradeoffs between using a charger IC with PSEL & PG pins vs. an IC with the D+ & D- pins

Dan Ringger
Intellectual 1790 points
Part Number: BQ24259
Other Parts Discussed in Thread: BQ27742-G1, BQ25606

One of our potential battery pack suppliers has recommended a Li-Polymer battery pack (~4200mAh capacity). 

 

The battery pack includes a TI BQ27742-G1 (or equivalent)  http://www.ti.com/product/BQ27742-G1   Fuel Gauge/Protection IC that will be part of the battery pack.

 

The battery pack supplier recommends the following TI battery charger ICs to charge the battery pack.  The charger IC will NOT be a part of the battery pack but rather will be located on our main PCB.

 

BQ24259RGER

BQ24295RGER

BQ24296RGER

BQ24297RGER

BQ24298RTWR

 

Questions

 

    1. Both the fuel gauge/protection IC and the battery charger IC(s) have temperature sensing functions.  Are we to use both temperature sensing functions or are we to bypass the charger IC temperature sensing function and make use of the fuel gauge IC temperature sensing function since it will better reflect the battery temperature?  Please provide details.

 

    1. We are trying to understand the tradeoffs between using a charger IC with PSEL & PG pins vs. an IC with the D+ & D- pins.  Can you provide guidance on this?

 

 

  • 0
    TI__Genius 10240 points
    Dan,

    When the system has both charger and gauge, the charger temperature sensing is bypassed and the fuel gauge IC temperature sensing is used for better accuracy and system control.

    Using PSEL and OTG to set the input current involves host detection and setting. The host detection offers the flexibility to detect any port the device will attach to. The D+D- detection does not need host involvement, the communication via D+D- needs to wait the completion of D+D- detection.
  • 0 in reply to ezhao
    TI__Intellectual 1790 points

    Hi Eric,

    Thanks for the top level feedback.  We need a lot more technical details quickly as we are in process of putting a schematic together. 

     

    Overview

     

      • Battery pack will use BQ27742-G1 (or equivalent) fuel gauge IC (this IC/circuit will be part of the battery pack).

     

      • Our main PCB will most likely use one of the following charger ICs:  

     

        • BQ24259RGER
        • BQ24295RGER
        • BQ24296RGER
        • BQ24297RGER
        • BQ24298RTWR

     

      • Our main PCB will also have an MCU.

     

    Questions

     

      1. Per your reply below about bypassing the charger IC temp sensor function…. How exactly is this done with the charger ICs listed above?  Please provide schematic snippets if needed.

     

      1. How are the MCU and charger IC to interconnect if the charger IC performs D± detection?’

     

      1. How is the MCU to know it can begin negotiation with a host system?

     

      1. Ideally, we think we would like to keep our MCU as much “out of the loop” as possible.  Comments?

     

        1. Do the charger ICs have the ability to become an I2C host?

     

      1. Can you provide an overview of the (5) charger ICs listed above to help us make the final choice for our design?

  • 0 in reply to Dan Ringger
    TI__Mastermind 25800 points

    Hey Eric,

    To your questions:

    Dan Ringger said:

      1. Per your reply below about bypassing the charger IC temp sensor function…. How exactly is this done with the charger ICs listed above?  Please provide schematic snippets if needed.

    You may bypass by putting two 10k resistors in series from REGN to GND, with the common node connected to the TS pin. You can refer to our EVM as a reference, where there is an optional 10-kOhm in series with the Low-Side resistor on the TS pin (30.1-kOhm) and hte High-Side resistor from TS to REGN is a 5.23-kOhm. 

    Dan Ringger said:
      1. How are the MCU and charger IC to interconnect if the charger IC performs D± detection?’

     

    The MCU and Charger do not interface through the USB lines. There devices are connected through the I2C interface.

    Dan Ringger said:
      1. How is the MCU to know it can begin negotiation with a host system?

    I'm guessing this has some relation to your previous question, so I make a point about USB D+/D- communication (again this is different from I2C communication). For the D+/D- detection on the charger, the Host MCU must relinquish control of the lines (either through tri-stating the pins or through a USB switch) and wait for the USB detection to complete before you start USB enumeration. If you plan on using this D+/D- detection feature on the chargers, I would recommend waiting approximately 1s after a VBUS plug-in event to begin enumeration.

    Dan Ringger said:
    1. Ideally, we think we would like to keep our MCU as much “out of the loop” as possible.  Comments?

       

      Our chargers have default settings is there is no MCU controlling them, but you will have to confirm if those charge settings are right for your battery. Other than that, the MCU has to be involved or you can go with a standalone device like the BQ25606 where you just input power and all settings are set by the external hardware.

      Regards,

      Joel H