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BQ25750: regarding buck boost required in my case or not

karan mittal
Prodigy 70 points
Part Number: BQ25750
Other Parts Discussed in Thread: BQ25756E, BQ25856-Q1

Tool/software:

I am going to use BQ25750 in my design, i wanted to know i will be having input voltage always right like my battery will be 29.4 so my input voltage will also be 29.4 or 29.6 that i can adjust .

so my question do i still need to use buck boost circuit of BQ25750 or i can just leave that section in my design .

Please provide your important feedback

  • 0
    TI__Mastermind 30965 points

    Hello Karan,

    Thanks for working with this part. If you are going to have VAC=VBAT in the circuit, I would recommend a buck-boost topology. The buck-boost topology will boost the voltage if the input voltage drops down below the VBAT voltage. 

    For example, if the input voltage drops below VBAT, the the charger could trigger IAC_DPM in the charger and limit the input current to keep the input voltage from falling further. The charger could then boost the input voltage to keep charging the battery. 

    Let me know if you have any questions. Let me know if there's anything else about your application that might influence Buck compared to Buck-Boost topology.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 70 points

    Hi Ethan 

                     that i understood, i am having this type of charger more then 5 in my design , i can use 1 buck boost convertor in input for all 5 of the chargers and avoid buck boost for each charger . 

    but correct me if i am wrong this buck boost charger also takes care of CV mode , CC mode , tickle charge .

    so this circuit is also required for other purposes beside boosting voltage .

    please Guide 

    thanks

  • 0 in reply to karan mittal
    TI__Mastermind 30965 points

    Hello Karan,

    So your design would be to have 1 buck-boost charger that tracks the battery voltage, then 5 buck chargers take the voltage from the buck-boost and charge the battery?

    Could you use a Vin of 30V and 5 buck chargers to charge a battery?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 70 points

    Hi 

          for this question So your design would be to have 1 buck-boost charger that tracks the battery voltage, then 5 buck chargers take the voltage from the buck-boost and charge the battery? 

    i have battery of 7cell so max around 29.4 volt and my power supply for charging will be 24 volt 

    i have 5 batteries which needs to be charged all at one time so 5  BQ25750 charger ic i am thinking to use which has buck boost both ,

    my question are

    1) if i use one boost DC DC convertor which is placed between smps 24 volt out and chargers input will chargers buck boost circuit will be still required ?

     2) if i use one boost DC DC convertor which is placed between smps 24 volt out and chargers input will that make sense for EMI EMC issues because now         only one DC DC convertor is creating EMI and that also is shielded?

    Thanks

    Regards

    Karan

  • 0 in reply to karan mittal
    TI__Mastermind 30965 points

    Hello Karan,

    Thanks for the clarification.

    1. If you use a DC-DC converter to boost the circuit beforehand, you will not need the boost portion of the IC.

    2. I'm not sure about the effect on EMI here. For the BQ25750 in most operating regions, only the buck part or the boost part is operating. Only in the narrow buck-boost region are both the buck part and boost part switching.

    The BQ25750 does require all 4 FETs to switch though. We are coming out with a buck-only version of the BQ25750 in the next couple of months though.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 70 points

    ok thanks for all the information.

    one doubt was their that what would be production life of BQ25756E , so that we can consider it in our design .

    Thanks

    Karan  

  • 0 in reply to karan mittal
    TI__Mastermind 30965 points

    Hello Karen,

    The BQ25756E will stay in production for a very long time. It's a new part designed for medical and industrial applications.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 70 points

    Hi we found BQ25856-Q1 automotive grade one so is it direct replacement for BQ25756E these series .

    if i want to use automotive grade one can i use this .

  • 0 in reply to karan mittal
    TI__Mastermind 30965 points

    Hello Karan,

    Yes, that is possible. The BQ25856-Q1 is pin-to-pin with the BQ25756E.

    Let me know if you have any other questions.

    Best Regards,
    Ethan Galloway