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BQ32002: battery supply voltage at "operating "and "switchover"

Ken Zhang
Intellectual 1945 points
Part Number: BQ32002

HI,

         Two questions: 

    Q1: what does  Vback at "Operating" and "Switchover" mean? if Vback <1.4V, the BQ32002 will be shut down and no any time counting, right?

Q2: What is relationship between Vback at "Switchover"  and that listed in Figure 4?

  • +1
    TI__Expert 6110 points

    Hi Ken, 

    1. The BQ32002 is in "switchover" mode for a short duration after VCC falls below Vref, and is in "operating" mode once it is being fully powered by the backup source. To ensure the switchover sequence happens properly, Vback should be greater than Vref (1.8 V) with some margin, which is why the datasheet has a minimum requirement of 2 V. If Vback < 1.4 V while the BQ32002 is using the backup source (essentially if Vback and VCC are both less than 1.4 V), then the device will shut down. 

    2. The diagram in Figure 4 visually shows the conditions that cause VCC or Vback to be used as described in section 7.3.2. To summarize, if VCC > Vback or VCC > Vref then VCC will be used the power the device, and if VCC < Vref < Vback, then Vback will be used instead. 

    Regards, 

    Connor 

  • 0 in reply to Connor Lewis
    TI__Intellectual 1945 points

    Connor

          pls check if below my understand is right.

            after finish "switchover" transition, the backup source, for example, a battery,  will provides power to BQ32002. Then backup source voltage will be gradually drop. During backup source voltage drop duration, BQ32002 still can work in "operating" mode till Vbackup voltage drops to 1.4V. is it right?

  • +1 in reply to Ken Zhang
    TI__Expert 6110 points

    Hi Ken, 

    Yes, that is correct as long as the backup source can provide enough current at that voltage as well. 

    Regards, 

    Connor 

  • 0 in reply to Connor Lewis
    TI__Intellectual 1945 points

    Hi, Connor

          I had some confused about above #1. "To ensure the switchover sequence happens properly, Vback should be greater than Vref (1.8 V) with some margin, which is why the datasheet has a minimum requirement of 2 V". but in Figure 4 list in #2, the switchover is still shown as Vback < Vref (=1.8). Does it  mean that switchover is still implemented even Vback < 1.8?

  • 0 in reply to Ken Zhang
    TI__Expert 6110 points

    Hi Ken, 

    I believe that specific chart is meant to show the device won't switch to Vback unless Vcc is less than both Vback and Vref. In practice, it is recommended to keep Vback > 2 V. 

    Regards, 

    Connor