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BQ24618: Using this as a current regulator and a few other questions.

Kim Drange Hansen
Prodigy 20 points
Part Number: BQ24618

Tool/software:

Hello, I am working on a charging system. In this system I have already included a MOSFET switch for the power source, a system to ensure no unwanted backwards current, and a coloumb counter for determining the charge of the battery as well as a microcontroller to manage all these aspects. I have a few questions about using the BQ24618 as a current regulator:

 1.

Is the "regulation voltage" set by the equation

where the device is set into its voltage regulation phase by the VFB pin being tripped over 2.1V?

2.

If I have already implemented a system to turn on and off charging based on the battery's estimated capacity, is it feasable to keep the device in the "current regulation phase" the entirety of the time it is operating and simply turn it off by toggling the CE pin? For example, if I want to charge a 6S li-ion battery and set the "Vbat" to 25V, could I simply turn the device on when I would like to charge the battery with a constant current and off when I have detected that it has received enough charge and have it stay in the "current regulation phase" the entire charging cycle?

3.

Is the fastcharge timer the same as the safety timer and is it reset if the device is turned off and back on again by turning off and on the CE pin? I do not see the "fascharge timer" mentioned anywhere else in the documentation.

4.

Since I already have a system to protect against unwanted reverse current, could I leave the "BATDRV" pin floating and exclude the MOSFET between the battery and the rest of the system in the typical applications diagram without any issues in the operation of the device?

  • +1
    TI__Mastermind 32941 points

    Hello Kim,

    Kim Drange Hansen said:
    Is the "regulation voltage" set by the equation

    Yes, This is correct.

    Kim Drange Hansen said:
    If I have already implemented a system to turn on and off charging based on the battery's estimated capacity, is it feasable to keep the device in the "current regulation phase" the entirety of the time it is operating and simply turn it off by toggling the CE pin? For example, if I want to charge a 6S li-ion battery and set the "Vbat" to 25V, could I simply turn the device on when I would like to charge the battery with a constant current and off when I have detected that it has received enough charge and have it stay in the "current regulation phase" the entire charging cycle?

    I don't see any obvious issue that would prevent this.

    Kim Drange Hansen said:
    Is the fastcharge timer the same as the safety timer and is it reset if the device is turned off and back on again by turning off and on the CE pin? I do not see the "fascharge timer" mentioned anywhere else in the documentation.

    Yes, they are the same. It's the Fastcharge Saftey Timer.

    Kim Drange Hansen said:
    Since I already have a system to protect against unwanted reverse current, could I leave the "BATDRV" pin floating and exclude the MOSFET between the battery and the rest of the system in the typical applications diagram without any issues in the operation of the device?

    Are you going to use this device in battery only mode? The BATFET is used to connect battery to SYS when adapter is not present, so the SYS load will reciceve power.

    Best Regards,

    Christian

  • 0 in reply to Christian Moyer
    Prodigy 20 points

    Thank you for your answers. 

    I have a seperate system for point 4 which connects the adaptor to and disconnects the battery from the system during charging and does the opposite during discharge, and so if I could remove the BATFET without affecting the IC or the surrounding circuit, this would be desirable for marginally higher efficiency and the slight lowered cost of not having to use an additional MOSFET. So you say there is no problem with leaving the BATDRV pin floating in this case?

    Also, would you recommend that I pull the TTC pin to GND or VREF to not have the timer as I already have a system for managing the battery's safety?

  • +1 in reply to Kim Drange Hansen
    TI__Mastermind 32941 points

    Hello Kim,

    Kim Drange Hansen said:
    I have a seperate system for point 4 which connects the adaptor to and disconnects the battery from the system during charging and does the opposite during discharge, and so if I could remove the BATFET without affecting the IC or the surrounding circuit, this would be desirable for marginally higher efficiency and the slight lowered cost of not having to use an additional MOSFET. So you say there is no problem with leaving the BATDRV pin floating in this case?

    I see no obvious issue with leaving BATDRV floating.

    Kim Drange Hansen said:
    Also, would you recommend that I pull the TTC pin to GND or VREF to not have the timer as I already have a system for managing the battery's safety?

    I would recommend pulling up to VREF.

    Best Regards,

    Christian.