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BQ24650: Replace UC2906DW with BQ24650

user3502896
Prodigy 70 points
Part Number: BQ24650
Other Parts Discussed in Thread: BQ24610, UC2906, BQ25713, BQ25710, BQ24450

Hello

at the Moment i design a new system with lead acid batteries.

My System hat 24 V DC Supply an 2 Leadacid batteries in Series.

At the Moment i use the compination Step up converter and UC2906DW.

I like to change the batterie charger to the BQ24650. I guess that i did not need a step up converter.

Know my Question:

Can the BQ24650 charger two lead acid batteries in Series? Every Battery has 12 C DC. At the moment i Charger with 27.6 V

If the Power is lost i switch a Relais to supply from the batteries.

Can some help me in this case?

Kind Regards Oliver

  • 0
    TI__Mastermind 24075 points

    Hi,

    BQ24650 has a recommended maximum input voltage rating of 28V, and supports a battery voltage of upto 26V. As this is a buck charger, it requires an input voltage higher than the output voltage and the minimum threshold is defined by the SLEEP comparator, which can be found in the EC table of the datasheet. If you are not using a solar panel as your input source it is recommended to use BQ24610 instead, as the mechanism to charge the lead acid batteries is the same for 610 as it is for 650.

  • 0 in reply to Kedar Manishankar
    Prodigy 70 points

    Hello Thanks for your answer.

    I think i have to discripe my problem one more time.

    I search for a Solution without step up.

    So my first idea was the BQ24650 i think there is a step up funktion includet.

    I made a drawing for better discusionBRN3C2AF4CED649_000008.pdf

  • 0 in reply to user3502896
    TI__Mastermind 24075 points

    Hi,

       I cannot read the text for what is in between output of BQ24650 and SYSTEM. This is a valid way of using BQ24650, as you can refer to the user guide which contains the EVM schematic where this configuration is implemented. in the EVM a simple diode is placed between the battery and SYS, so that when input adapter is present, the diode will reverse bias and adapter will solely provide SYS, and when adapter is removed, the diode will forward bias and battery will provide SYS.

  • 0 in reply to Kedar Manishankar
    Prodigy 70 points

    Hello

    Between the BQ24650 an the System is relay. In Case the external 24V supply has a breakdown, the relay switch the battreries to the system.

    I do not use a diode, cause my normal voltage is 24 Volt an not 27,6 V.

    I have a solution with the UC2906 but i think this IC is very old an the new one is better.

  • 0 in reply to user3502896
    TI__Mastermind 24075 points

    Hi User,

    What is the maximum charge voltage of your batteries? What value will you be looking to configure the charge regulation voltage of the BQ24650 to?

  • 0 in reply to Kedar Manishankar
    Prodigy 70 points

    Hello

    the maximum charge voltage of the Batteries is 28,2 Volt. I will set it to 27.6 Volt.

    My Inputvoltage for the charger is24 Volts.

    Kind regards Oliver

  • 0 in reply to user3502896
    TI__Mastermind 24075 points

    Hi Oliver,

      This is not a possible use case for BQ24650. BQ24650 is a buck charger, which means it steps down the input voltage to the output voltage, and needs an input voltage higher than the output voltage. The SLEEP specification in the datasheet is the minimum difference between input and output voltage that the charger needs to remain operational. In SLEEP mode the charger is disabled and enters a low quiescent current mode, so for your system the charger would be disabled as battery nears full charge. For such a system you would need to incorporate a buck-boost charger, which could handle buck charging when battery is discharged, and boost charging when battery is near full charge (higher than input voltage).

    This is what I referenced in the first response as well. For buck-boost portfolio you can refer to BQ25713 or BQ25710 depending on communication interface preference SMBus vs I2C. There is no standalone buck-boost charger.

  • 0 in reply to Kedar Manishankar
    Prodigy 70 points

    Hello

    i think the bestway is a step up converter to 32 Volt.

    For charging i think the best Way ist to use UC2906DW or BQ24450.

    So i can use a standart applikation.

  • 0 in reply to user3502896
    TI__Mastermind 24075 points

    Hi,

       The issue with BQ24650 is that the max recommended operating condition is for a 28V max input voltage, so stepping up 24V input adapter to 32V would not be feasible. Even though the abs max is rated higher than this, we do not recommend using larger than a 28V input voltage applied to VCC of BQ24650. This is not enough headroom for your charge regulation voltage, for the charger to be able to operate correctly. I am not familiar with the UC2906DW so I cannot comment on that