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BQ20Z95/BQ20Z75-v180 General Questions

Nick56152
Intellectual 545 points
Other Parts Discussed in Thread: BQ20Z75-V180, BQ20Z65-R1, BQ20Z45-R1

I am in the process of completing a LiPo battery powered design and intend on using one of these ICs (BQ20Z95 or the BQ20Z75-v180) for the purpose of gas gauging and 1st and 2nd level protection (I do not require any  of the charging features).

My questions are:

1. As the LiPo battery is the sole power source for the design, by simply pulling the SYSTEM PRESENT pin to ground (via an POWER switch on the design) when turning on the device with the LiPo battery connected, will I be able to enter discharge mode and hence power my design? (I am doubtful as I keep reading that an external power source is required to turn on the IC...)

2. Just to double-check, *PULL-DOWN* (not pull-up) resistors to ground are required at both ends of the SM bus (at the MCU and at the battery management IC). Correct?

3. Is the the LED display feature the only main difference between the BQ20Z95 and the BQ20Z75-v180?

I'd really appreciate it if anyone with experience with these ICs could help me answer these questions.

Cheers,

Nick

 

 

 

  • 0
    Intellectual 545 points

    EDIT:

    After doing further reading, I have to decided to choose between the newer BQ20Z45-R1 and BQ20Z65-R1.

    Still, my main concern is whether I can protect/monitor my LiPo-powered design with these ICs without the need for an extra or external power supply (the design will not have charging capabilities -> the LiPo battery is to be removed and charged by a separate battery charger).

    Nick

     

  • 0 in reply to Nick56152
    TI__Expert 3865 points

    Nick,

    If you're interested in using z-track on LiPO4 battery, you should choose bq20z4x or bq20z6x series.

    You will need to "jump start" the device (i.e. apply a charger to the PACK terminal) only if you just connect the battery pack to the pcb or when the device is in shut down mode.

    Afterward, the device is powered by the battery.

    We recommend a 1M pull-down on the SMBus in order for the device to enter sleep mode. You can have it on either the host side or the pack side.

  • 0 in reply to Jackie Hui
    Intellectual 545 points

    Thanks for the reply Jackie!

    I'll probably end up using the bq20z65-R1 I think...

    Ah - I thought this may be the case:

    So just to verify, if my design is OFF with the battery pack connected, I'll have to *momentarily* apply a power source to the PACK terminal to make the IC start powering the design?

    Which charging IC do you recommend for use with the bq20z65-R1?

    And finally, do I need pull-downs on both the host and pack side do I if they aren't right next to each other? (they are actually on separate stacked PCBs...)

    Thanks so much for your help so far!

    Nick

  • 0 in reply to Nick56152
    TI__Expert 3865 points

    Yes, if the device is OFF, you should apply a power source across PACK+ and PACK- to jump start the device.

    You can have pull-downs on both the pack and the host side - actually, you do want to have one on the pack side so that the battery pack can enter sleep mode without connect tot the host.

    I'm not familiar with charger IC, but I'll ask the charger team for advice. You can also post the question to the charger forum.

  • 0 in reply to Jackie Hui
    Intellectual 545 points

    Thanks again Jackie.

    That's interesting that the IC needs to be jumpstarted... Out of curiosity, how do laptops when not plugged into an external power supply make use of the IC?

    A couple more questions:

    1. The host in my design is a microcontroller which is actually powered by the LiPo battery pack itself. With the entire design OFF, and then jumpstarting with an external power supply at PACK+ and PACK-, will the IC turn on (i.e turn on the discharge MOSFETS) without the need to communicate with the host microcontroller? (as the microcontroller will have no power yet!).

    2. Related to the above question, won't using pull-downs on the SMBus lines keep the IC in shutdown mode as it will always assume there is no host present because the LiPo pack powers the host microcontroller?

    I hope these questions make some sense!

    I appreciate all your help so far.

    Nick

  • 0 in reply to Nick56152
    Intellectual 545 points

    Is anyone able to shed some light on the answers to my most recent questions?

    Much appreciated,

    Nick