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BQ24074: Peak current requirement

Dharani MP
Prodigy 10 points
Part Number: BQ24074
Other Parts Discussed in Thread: BQ24075, BQ24079

We are working on a 4G automotive GPS tracker where the peak power requirement would be 12W (4V @2A & 3.3 @1A).

The system will have one integrated Li-ion cell. We like to use BQ 24073/74/75 as it's automotive grade Linear chargers.

The concern is the mentioned chargers supports maximum 1.5A at it's input (IN PIN).

Do this limits or impact peak power requirements in a worst case like a disconnected or deeply discharged battery ?

  • 0
    TI__Mastermind 23200 points

    Hi Dharani,

    Welcome to E2E!

    Will these peak power requirements be in short bursts at regular intervals? If there is a battery connected, the battery can provide supplement current if the input current is not sufficient. For a deeply discharged battery, the output voltage may fall and the device may consider it a short circuit if the voltage falls for the short circuit duration.

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Thank you Anthony for the prompt response.

    Yes, short bursts are expected at regular intervals.

    For a deeply discharged battery, does any linear chargers support under voltage lockout or what would be the best method to circumvent such a scenario.

    Thank you

  • 0 in reply to Dharani MP
    TI__Mastermind 23200 points

    Hi Dharani,

    Yes, the linear chargers do support under voltage lockout (UVLO). A possibility here if the supplement mode is not enough is to use FETs to disconnect the battery from the charger when not charging and connect it directly the load so that the load can pull from the battery. You can save on one FET by using the SYSOFF variants of the BQ24074 such as the BQ24075 and BQ24079. This is a solution I've seen for this use case. 

    Best Regards,

    Anthoyn Pham

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Thank you Anthony, sorry for the delay in our response. We were finalizing the design and having one question.

    As BQ24075 datasheet says 5.5 regulated output (with normal input range) if we need output of 4.4V, are we good to provide an input of 4.4 to BQ24075. We plan to use peak current of 1.5A as well. Please share your valuable thoughts on such a design

  • 0 in reply to Dharani MP
    TI__Mastermind 23200 points

    Hi Dharani,

     Yes if you were to use the BQ24075 to take advantage of the SYSOFF functionality, you would need about a 4.4V input to have an output of 4.4V. This would be  fine. You will need to take into account the IN to OUT dropoff from the Q1 FET at higher current loads (typically 300mV at 1A load).

    Best Regards,

    Anthony Pham