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BQ79606A-Q1: Queries

PRAHLAD Supeda
Expert 6150 points
Part Number: BQ79606A-Q1

Customer is considering using BQ79606A-Q1. And need following clarificaitons.

1. if manual cell balance is used, can UV/OV function be used during the cell balancing? Because customer need to cell balance but can't stop to use the hardware comparator. 

 Is there isolation between the two functions (ADC and comparator function)? 

2. Is there a REX on the BQ79606A-Q1? 

Have notified customer for posting direct response / further queries to this thread.

  • 0
    TI__Genius 9401 points

    Hi,

    Thanks for your questions. Please see my answer below.

    1. If cell balancing is enabled, OV/UV cannot be used since the measurements will be inaccurate. To explain a little more why this happens: the OV/UV comparators are on the CB pins, and if cell balancing is enabled, the voltage measured at the CB pin will be off from the real battery voltage. This is because there is a higher current flowing on the CB pins (balance current) and therefore there is a higher IR drop on the external resistor.

    Regarding your questions about isolation between ADC and comparator function, I'm not sure what you mean by "isolation". The ADC uses the VCx pins, whereas the OV/UV comparators use the CBx pins. See page 19 Functional Block Diagram of bq79606A-Q1 datasheet ( http://www.ti.com/lit/ds/symlink/bq79606a-q1.pdf )

    Can you please explain what you mean by REX?

    Regards,

    Leslie

  • 0 in reply to Leslie Marquez
    Prodigy 75 points

    Hi,

    Thanks for the response, I am the consumer.

    So even in manual cell balancing, it is impossible to cell balance and to use the UV/OV comparator.

    To be more precise about the isolation question, we want to use the BQ79606A for security product and we need to know the voltage isolation between the two way of measuring (ADC and UV/OV comparator). 

    The REX is the return of experience, because the chip is new and we want to know if there is documentation or ohter things abour the return of experience.

    Sincerely,

    Pierre.

  • 0 in reply to Pierre Le Bouar
    TI__Genius 9401 points

    Hi Pierre,

    It is possible to leave the OV/UV comparators on when balancing (as long as you don't enable CBDone threashold), but we do not recommend it because the measurement won't be accurate. As I mentioned above, the OV/UV comparators are on the CB pins, and if cell balancing is enabled, the voltage measured at the CB pin will be off from the real battery voltage. This is because there is a higher current flowing on the CB pins (balance current) and therefore there is a higher IR drop on the external resistor.

    Regarding for question about the ADC and UV/OV comparator, we don't have a specification for voltage isolation between these different circuits. These are different circuits in different device pins (ADCs on VC pins and OV/UV comparators on CB pins). Please see section 8.2 Functional Block Diagram on page 19 of the device datasheet. : http://www.ti.com/lit/ds/symlink/bq79606a-q1.pdf

    Regarding the REX, we don't have this. 

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Genius 9401 points

    Hi Pierre,

    To add to my answer above, when you enable balancing you will be discharging the cells with higher voltage to be able to match the voltage of all cells. Because of this, the bq79606A-Q1 device has a VCBDone threshold feature: When CB_DONE_THRESH is enabled (in CB_DONE_THRESH register), the device will stop balancing when the voltage on the cell reaches the threshold specified in the CB_DONE_THRESH register.

    See section 8.3.5 Cell Balancing of the device datasheet:

    http://www.ti.com/lit/ds/symlink/bq79606a-q1.pdf

    Best regards,

    Leslie