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bq40z50 parameters

Other Parts Discussed in Thread: BQ40Z50, BQ78350, BQ76920

I have several questions regarding bq40z50 operation:

1. What are data found in Calibration->Current , namely CC Gain and Capacity Gain ?

Are they the value of the shunt resistor used in my application? Because I did set these two parameters to value 5.2 (mOhm) so now bq reports the discharging and charging current correctly.

2 .How do I do the scaling of voltage and current?  (if i use an application which has a battery pack for example 48 V/100Ah what values will I modify -like voltage and current gain- in order to get real data ? )

3. If i update the bq data flash with the values provided by  the corresponding battery file found under Chemistry tab, do I need to set/modify the values of protection thresholds and the values of advanced charging algorithm? Or those values in the file will do just fine given I have specified the number of cell , design capacity ?

4.I have not found very much informations about AFE. What are its features?

5.  Is Cell x CompRes parameter found under Register tab in Battery Management Studio the same as Cell Resistance found in bq Reference Manual (page.13) ?

6. In Reference Manual they say about Rsense used for calculation of  thresholds for overload protection. Is Rsense a parameter I can modify in Battery management Studio or represent the shunt resistor value used in my design?

7. What is the time constant of Average Current? Or , after what time the Average Current becomes equal with the instantaneous current ?

8. If bq enter is one of the permanent fail protections the FETs are turned off. Are they turned off for ever? Can't the CHG/DSG process be restarted? Or I should just change the bq?

9. My bq reports a voltage bigger on PACK side that on BAT side (~50mV difference) (without charger, when discharging)

10. Should I consider Cell grid , Pack grid values ; Ra table values ?

11. How to use  Cell gain , Pack gain , Bat gain values? For example in my case for a  pack voltage of 12 V bq reports a pack gain of 49 thousands. Bat Gain is slightly lower ( ~48 thousands )

  • Hi Ionut,

    I am looking into your inquiry. I will get back to you.

    Best,
    Justin
  • 1. What are data found in Calibration->Current , namely CC Gain and Capacity Gain ?

    Are they the value of the shunt resistor used in my application? Because I did set these two parameters to value 5.2 (mOhm) so now bq reports the discharging and charging current correctly.

    CC Gain This is the gain factor for calibrating Sense Resistor, Trace, and internal Coulomb Counter (integrating ADC delta sigma) errors. It is used in the algorithm that reports Average Current. The difference between CC Gain and CC Delta is that the algorithm that reports Current cancels out the time base because Average Current does not have a time component (it reports in mA) and CC Delta requires a time base for reporting Remaining Capacity (it reports in mAh). Normal Setting: CC Gain should never need to be modified directly by the user. It is modified by the current calibration function from Calibration mode.

    CC Delta This is the gain factor for calibrating Sense Resistor, Trace, and internal Coulomb Counter (integrating ADC delta sigma) errors. It is used in the algorithm that reports charge and discharge in and out of the battery through the Remaining Capacity register. The difference between CC Gain and CC Delta is that the algorithm that reports Average Current cancels out the time base because Average Current does not have a time component (it reports in mA) and CC Delta requires a time base for reporting Remaining Capacity (it reports in mAh). Normal Setting: CC Delta should never need to be modified directly by the user. It is modified by the current calibration function from Calibration mode.

    2 .How do I do the scaling of voltage and current?  (if i use an application which has a battery pack for example 48 V/100Ah what values will I modify -like voltage and current gain- in order to get real data ? )

    What battery configuration are you using to have 48V/100Ah? Is it 12-Series? If so you will not be able to use this gauge since the BQ40z50 supports up to 4-Series configuration. I would recommend looking at the bq78350 + bq76920 AFE. Note that this will provide gauging capability but not cell balancing.

    3. If i update the bq data flash with the values provided by  the corresponding battery file found under Chemistry tab, do I need to set/modify the values of protection thresholds and the values of advanced charging algorithm? Or those values in the file will do just fine given I have specified the numberof cell , design capacity ?

    The protection thresholds are set to recommended default values corresponding to the design capacity that is default to the gas gauge. However, you will need to modify these corresponding to your battery’s spec sheet. For example, number of cells and design capacity are probably going to need to be updated.

    4. I have not found very much informations about AFE. What are its features?

    Please take a look at the bq76920 AFE product page. Here you will find its datasheet, which includes its features.

    5.  Is Cell x CompRes parameter found under Register tab in Battery Management Studio the same as Cell Resistance found in bq Reference Manual (page.13) ?

    These look to be different. One is based on current multiplied by cell resistance; the other is temperature compensated. What do you need this information for in your system?

    6. In Reference Manual they say about Rsense used for calculation of  thresholds for overload protection. Is Rsense a parameter I can modify in Battery management Studio or represent the shunt resistor value used in my design?

    Yes, Rsense is the sense resistor value.

    7. What is the time constant of Average Current? Or , after what time the Average Current becomes equal with the instantaneous current ?

    The average current will not equal the instantaneous current unless the instantaneous is constant over time.

    8. If bq enter is one of the permanent fail protections the FETs are turned off. Are they turned off for ever? Can't the CHG/DSG process be restarted? Or I should just change the bq?

    There are FW and HW based protection. Most of the secondary protection can be reset from a commanded reset or POR. What do you mean change the bq?

    9. My bq reports a voltage bigger on PACK side that on BAT side (~50mV difference) (without charger, when discharging)

    This seems reasonable. You will have some IR drop. You should read the current and this should account for the 50mV drop. E.g. 10 amps across a 5 mOhm sense resistor will give you 50 mV of drop.

    10. Should I consider Cell grid , Pack grid values ; Ra table values ?

    You do not need to edit these parameters. These are updated as a result of impedance track.

    11. How to use  Cell gain , Pack gain , Bat gain values? For example in my case for a  pack voltage of 12 V bq reports a pack gain of 49 thousands. Bat Gain is slightly lower ( ~48 thousands )

    These gain values are internal to our calculations. Could you clarify why you need the specific gain values for the particular set of resistance tables?

  • I just needed some clarifications about the terms used in the specified document in order to understand if I need to use those parameteres or not. Now I know I don't. 

    Regarding permanent fail protections : there is no way to recover from this protections? A PF event will render bq useless for ever? 

  • Hi Ionut,

    This is not necessarily true. When your device undergoes a PF event, there are a series of protections that occur to prevent further damage (such as disabling the CHG and DSG FETs) These are defined in the TRM chapter 3 on permanent failure.

    In most cases, you will need to determine what was the cause of the PF and then remedy it, reconnect the pack and reset and you should be good then.

    Best,
    Justin