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BQ78350-R1: BMS:BQ78350+BQ76940,how to improve the overcurrent limit in the discharge protection?

user5811580
Intellectual 700 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76940, BQ78350, BQSTUDIO,

Hi, all.

We have just made a BMS to drive 12 motors, which is made up of BQ76940+BQ78350.

For the overcurrent limit in the discharge protection, we just set PROTECT 2 register as below:

 OCD_D[2:0]=b010,OCD_T[3:0]=b1110

RSNS=1

Besides, PROTECT 1 register is set as below:

SCD_D[1:0]=b01

SCD_T[2:0]=b110

In the end, OCD threshold is set to -32000mA.

The motor controllers just report "under voltage" error when running.

"Under voltage" is caused by not being able to provide enough current.

However, the bqstudio does not report any error during the running process.

What's the meaning of OCD threshold when set to -32000mA? 

Does it mean setting the overcurrent limit in discharge to 32A?

IS there any way to improve this limit?

  • 0
    TI__Guru* 81034 points

    Hi,

    If you are using the BQ78350-R1 and BQ76940 together, then the settings must be configured in the BQ78350-R1 data flash. The BQ78350-R1 controls the BQ76940 device and will set the SCD and OCD settings.

    The BQ78350-R1 has SCD and OCD settings for the BQ76940, but it also has additional current protections if software-based protection is needed too.

    The parameters for AOLD (See section 3.6 of the BQ78350-R1 Technical Reference Manual) sets the OCD for the BQ76940.

    The parameters for ASCD set the SCD settings for the BQ76940.

    Make sure both AOLD and ASCD are enabled for the BQ78350-R1 Enabled Protections settings.

    For the additional protections, the BQ78350-R1 has OCD which has more flexible threshold and delay. When you set this value to -32000mA, it means you are looking for a discharge current of 32A. You can modify this value to a value that suits your application.

    There are many parameters that must be configured for the BQ78350-R1. Please make sure to look at the following app note and the TRM:

    http://www.ti.com/lit/pdf/slua924

    http://www.ti.com/lit/pdf/sluubd3 

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 700 points

    Matt Sunna said:

    When you set this value to -32000mA, it means you are looking for a discharge current of 32A. You can modify this value to a value that suits your application.

    Hi, Matt

    The maximum value of OCD's threshold and delay is -32768mA.

    Does it mean that the maximum discharging current is only 32.768A?

  • 0 in reply to user5811580
    TI__Guru* 81034 points

    Yes, that is the maximum. However, if you download the firmware for BQ78350-R2 (http://www.ti.com/tool/BQ78350-R2-DEVICE-FW), you can use current scaling and go to much higher current values. You can scale by 10 or by 100 using the IPSCALE parameter. Many users use this feature for high current applications.

    The BQ78350-R2 firmware can be loaded onto the BQ78350-R1. In BQStudio, you can go to the Firmware screen and click the Program button with the new srec file. When you download the firmware, there will also be a .bqz file which you can copy to C:\ti\BatteryManagementStudio\config\ - This will allow BQStudio to automatically recognize the R2 device and display the R2 registers and Data Flash settings.

    Best regards,

    Matt