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BQ25710: BQ25710 Path Through Mode

Akihisa Tamazaki
Genius 12430 points
Part Number: BQ25710
Other Parts Discussed in Thread: BQ24780

Hello team,

Hello team,

Customer have some questions about BQ25710 Path Through Mode.

He is considering as below.
Input Voltage 12V
Battery NiMH 4cell (4.8V)
System power : 12V

Q1) Is the following operation possible with BQ25710 Path Through Mode?
      When Input voltage is 12V, BQ25710 supply 12V to the system and supply for charging 4cell NiMH.
      When Input voltage become 0V (turned off), BQ25710 supply 12V to the system  from  4cell NiMH.

Q2) When Input voltage change from 12V to 6V,  Can BQ25710 supply 12V to the system?

It may be easy question. Would you please advise?

Best Regards,
Akihisa Tamazaki

  • 0
    TI__Expert 3320 points

    Hi Akihisa:
        

        For Q1: Please confirm if customer input  source is adjustable.

                      We don't recommend to enable charge when in PTM if input voltage source is not adjustable. Especially given 12V fix input voltage and battery voltage is only 4V. Because when enable charge under PTM,the charge current should be (VBUS-VBAT)/RLINE(Rline is the distribution resistance from input voltage to battery terminal).The charge current( (VBUS-VBAT)/RLINE) will be increase fast when VBUS>> VBAT and trigger charge current limitation we set in register(ICHRG), then BQ25710 will switch back to buck boost mode the regulate the current average value to the charge current setting.  For example the waveform shown below. This just show the concept, for 12V/4V case it will be much worse I believe.

                      If input source is adjustable for flash charge, then story will be totally different.

                      We can't boost Battery voltage to system, but we can do OTG for the input side.

     For Q2:  Our 25710 is NVDC buck boost charger, which means the maximum system voltage is 180mV higher than battery fully charged voltage. You can consider BQ24780 for your application. 

    Regards

    Shishuo

  • 0 in reply to Shishuo Zhao
    TI__Genius 12430 points

    Shishuo-san,

    Thank you for your comment.
    I will talk with the customer and confirm the specification again.

    Best Regards,
    Akihisa Tamazaki


  • 0 in reply to Akihisa Tamazaki
    TI__Expert 3320 points

    In this case I will close the ticket for now and you can submit a new one if needed. Thanks.

    Regards

    Shishuo