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Help with Battery fuel gauge and cell balancing chips. Total Confusion

Lefteris Kostoulas
Prodigy 170 points
Other Parts Discussed in Thread: BQ24617, BQ40Z60, BQ40Z50-R1, BQ78350-R1, BQ76920, BQ76200, BQ78350, BQ40Z50, EV2400, BQSTUDIO

Good evening everyone,  i am  a junior electronics engineer and i am designing a new 4s 20Ah Li-po Battery management system for a portable instrument and i am somewhat confused regarding to the chips i  found so as to build it.

All i want to do is to supply the instrument through the 4s Li-po and, if the battery needs charging i will charge it through a wall adapter and also supply the instrument at the same time so as to function.   

For this purpose i was thinking of using a standalone charger chip with power-path . The bq24617. So far so good i think.

Next, i need a  balancing chip for the battery's cells. And here is where the confusion begins.

 After lots of searching and comparing chips it seems to me that there is no Standalone cell-balancing chip (to keep things as simple as possible) but instead i found these fuel gauge chips: bq40z60, bq40z50-R1, bq78350-R1  and
 these  monitor chips: bq76920, bq76200 that fit my requirements.

Now, the problem is that i don't know which of these chips would be the correct one to use (or in what combination) for my design  since all of them have, more or less as i see it, the same abilities and functions. For example all of them have Battery voltage monitoring ,Current monitoring, Temperature monitoring and most important cell balancing.

For example apart from the charger Should i use only bq76920 or (bq76920 together with bq78350) or bq40z50-R1?

I hope you can help,

Thank you for your time.

  • 0
    TI__Guru 73830 points
    Lefteris,
    You should consider the bq40z60 BMU for your application. This device integrates the gauge, charger and protector into one device and you can use a wall adapter as the supply to the bq40z60 charger.

    Tom
  • 0 in reply to ThomasCosby
    Prodigy 170 points

    Hello Sir,

    Well the bq40z60 seems the best solution for my design. But since i have minor experience with battery management (this is my first project) i need a chip (or a combination of chips) which can be used as standalone solution without  the use of an external micro-controller.

    That is why i thought that using  the  bq76920 + bq78350-R1 controller would be a good idea since these two  can communicate together without external programming (as far as i know), and also the standalone  bq24617 charger can work autonomously.  Please correct me if i am wrong.

    Of course if bq40z60 needs little or no programming ( i wish), i go for it all the way.

    Thank you for your time sir.

  • 0 in reply to Lefteris Kostoulas
    TI__Guru 73830 points

    Most of these devices will work autonomously without a host. The bq40z60 does not require uC. If you want to use a separate charger, then you can use the bq40z50. It is similar to the bq40z without the integrated charger.

  • 0 in reply to ThomasCosby
    Prodigy 170 points

    Great! That is good news.

    So, let me understand something here.

    Question 1: Since these devices do not require a uC or programming to function, the SMBus lines exist only to send to the optional host (uC) information about cell voltages, temperature (e.t.c.) and also to change the parameters of the bq40z50R1 through bq Studio?

    Question 2: Since i need to use a 4s 20Ah Li-polymer battery,  does the  bq40z50R1 automatically recognize the 4s Li-polymer battery or do i have to change any parameters inside the chip through programming with bq Studio? Because i don't have in my purchase EV2300 or EV2400 board to change the settings of the bq40z50R1.  So if changes must be made inside the bq40z50R1 then simply i cannot make them. So, in that case i must use another chip.

    Question 3: If NO programming is needed for bq40z50R1, can you tell me where can i find the default parameters for bq40z50R1?( The datasheet forwards the designer to the  technical reference book sluubc1b  which is a 250 pages... and i did not find any default parameters page. 

    Question 4: how can i understand from the datasheet if a device like bq40z60 works autonomously or if it needs some kind of programming from an external uC? Because by reading the datasheet description of these devices i couldn't tell if it was autonomous or not. Is there some sentence in the datasheet or something else which clarifies that?


    Sir thank you so much for your help.

  • 0 in reply to Lefteris Kostoulas
    TI__Guru 73830 points

    Here are some comments to your questions.

    Q1: The device does require some level of setup during the development phase and this is done using the SMBus interface and bqStudio. You have to configure parameters and run the optimization cycle to fine tune the device to your cells. The device does not require any interface to an external uC after this has been completed. You can use a uC to read parameters and monitor the pack, but it is not required.

    Q2: All of our multicell devices are configured for 3S and will need to be reconfigured to support a 4S pack. You will need to use one of the EV2x00 adapters and bqStudio.

    Q3: Programming is required as noted above and you should find the default settings along with the min and max range where each register is defined.

    Q4: The same answers apply to the bq40z60.

  • 0 in reply to ThomasCosby
    Prodigy 170 points
    Ok. This is bad news for me then but that is the way it is i assume.
    Since i cannot afford the purchase of a EV2300/400, from your point of view do i have any other option (some other chip from example that is standalone without the need of firmware)?
    Thank you sir
  • 0 in reply to Lefteris Kostoulas
    TI__Guru 73830 points
    Our gauges require some level of setup to configure the algorithm to the cells and configuration in your pack. The EV2300 or EV2400 adapter and bqStudio are required to complete this design phase, so I am not sure that you will be able to this device. Have you already purchased the bq40z60EVM?
  • 0 in reply to ThomasCosby
    Prodigy 170 points

    No i haven't purchased bq40z60EVM. I thought to build a pcb with bq40z60 by my own based on the datasheet schematic.

    Anyway i don't see it happening now. I will try to find out some other solution to this problem.

    Thank you for your time sir.