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BQ77915: protection application doubts & bq34z100 / bq78350R1-A for battery gauging

Mandar Mahajan89
Intellectual 345 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ34Z100, BQ78350-R1A, , BQ76940, BQ76920, BQ76930

hi ,

one of my customer intends to use below IC for which they need confirmation . 

kindly help to clarify - 

BQ7791506  
We are interested in using the bq7791506 IC for the protection application and wanted to clarify a few points regarding the part:-

 

1) We are looking to use this IC up to 200A continuous discharge current and 60-80A charge current. Do the charge overcurrent and discharge overcurrent protection limits support this if the sense resistor is sized accordingly & the CFET/DFET driver output can support larger MOSFET gate current?
2) We will be requiring the balancing current to be around 200mA and will be sizing the external balance MOSFETS and resistors accordingly but want to confirm that the Balance FET Drivers in the IC can be used for external operation and that the Balance FET drivers will be able to handle the higher balance FET size and hence gate current
3) Is there a max limit on the number of single ICs that can be cascaded for higher cell systems.
4) As per the datasheet, the overvoltage protection threshold for the particular IC is 3.8V, we are looking for a threshold of 3.6V. Is there some IC in the same lineup with this threshold as it is a standard threshold for LiFePO4?

 

5) We are looking to have a base 12V battery design and are looking at potential applications to support independent multiple 12V batteries in series to make a complete 24/36/48 V system. Are there any inherent issues in doing this? Please note that the single 12V blocks will be independent battery+BMS blocks.  


Is the above IC widely used in BMS applications in India or else? 

Is there any other part (for battery protection and balancing) that you would suggest that would meet our requirements as above?

 

BQ34Z100 / BQ78350R1-A  

We are considering the ICs bq34z100 / bq78350R1-A for battery gauging (State of Charge and State of Health) and would like to clarify the following points:-

 

1) Our batteries will be having a max capacity of 200AH with max discharge and charge currents as 200A and 80A respectively. Would the above ICs be suitable for the given specifications?

2) As per the datasheet, the BQ78350-R1A when used standalone would determine the SOC using a CEDV algorithm and not a coulomb counting algorithm. Could you comment on how accurate the CEDV algorithm is in comparison with the coulomb counting algorithm?

3) Does the  BQ78350-R1A require its companion front end for operation or can it be used with other front end such as the BQ7791506 (or other protection IC)?

I believe it needs communication from the front end which is not available in the  BQ7791506

Thanks 

Mandar

  • 0
    TI__Guru* 81035 points

    Hi Mandar,

    Yes, I think your customer also posted some of these questions to E2E today in these two threads:

    https://e2e.ti.com/support/power-management/f/196/t/933288

    https://e2e.ti.com/support/power-management/f/196/t/933279

    Please see my answers below in blue.

    BQ7791506  
    We are interested in using the bq7791506 IC for the protection application and wanted to clarify a few points regarding the part:-

     1) We are looking to use this IC up to 200A continuous discharge current and 60-80A charge current. Do the charge overcurrent and discharge overcurrent protection limits support this if the sense resistor is sized accordingly & the CFET/DFET driver output can support larger MOSFET gate current? The Device Comparison Table in the datasheet shows the different charge overcurrent and discharge overcurrent limits available. I do not think there is a version of the device that will meet their exact needs (charge overcurrent to discharge overcurrent ratio and the OVP they are requesting). For driving multiple FETs to allow higher gate current, this app not may be helpful: https://www.ti.com/lit/pdf/slua773
    2) We will be requiring the balancing current to be around 200mA and will be sizing the external balance MOSFETS and resistors accordingly but want to confirm that the Balance FET Drivers in the IC can be used for external operation and that the Balance FET drivers will be able to handle the higher balance FET size and hence gate current. Yes, the device can control external balance FETs to support higher currents.
    3) Is there a max limit on the number of single ICs that can be cascaded for higher cell systems. There is not a max limit, but for cell count beyond 20S, you should carefully understand and consider any timing delays due to stacking. The datasheet and BQ77915 stacking app report both have good information on this topic: https://www.ti.com/lit/an/slua906/slua906.pdf
    4) As per the datasheet, the overvoltage protection threshold for the particular IC is 3.8V, we are looking for a threshold of 3.6V. Is there some IC in the same lineup with this threshold as it is a standard threshold for LiFePO4? The Bq7791506 is used for LiFePO4 applications. This is the lowest available OVP device available.

     5) We are looking to have a base 12V battery design and are looking at potential applications to support independent multiple 12V batteries in series to make a complete 24/36/48 V system. Are there any inherent issues in doing this? Please note that the single 12V blocks will be independent battery+BMS blocks.  This is commonly done, just each battery will need to operate independently (cell balancing only between cells within the same block, different protection FETs for each block, etc.)


    Is the above IC widely used in BMS applications in India or else? Yes

    Is there any other part (for battery protection and balancing) that you would suggest that would meet our requirements as above? I think a battery monitor might be a better option if there is not a protector with the exact current and voltage thresholds they need. A battery monitor like the BQ76940 can work with an MCU to provide the protections they need. A battery monitor also needs an MCU or companion controller (BQ78350-R1A)

     BQ34Z100 / BQ78350R1-A  

    We are considering the ICs bq34z100 / bq78350R1-A for battery gauging (State of Charge and State of Health) and would like to clarify the following points:-

     1) Our batteries will be having a max capacity of 200AH with max discharge and charge currents as 200A and 80A respectively. Would the above ICs be suitable for the given specifications? Yes, these gauges can both be set up for higher capacity applications.

    2) As per the datasheet, the BQ78350-R1A when used standalone would determine the SOC using a CEDV algorithm and not a coulomb counting algorithm. Could you comment on how accurate the CEDV algorithm is in comparison with the coulomb counting algorithm? The CEDV algorithm is a coulomb counting algorithm, it just also compensates for current load and temperature for better accuracy.

    3) Does the  BQ78350-R1A require its companion front end for operation or can it be used with other front end such as the BQ7791506 (or other protection IC)? It requires the companion battery monitor (BQ76940, BQ76930, or BQ76920)

    I believe it needs communication from the front end which is not available in the  BQ7791506

     Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 345 points

    Thank You Matt for the detailed explanation . 

    this is indeed helpful . 

    Thanks

    Mandar