BMS with BQ76952

Hi Shashidhar,

I will need a bit more information to help troubleshoot the issues you listed.

First, you mentioned an "AFE board."  Are you using the BQ76952EVM, or just the BQ76952 device?

For question 1, does your MCU support clock stretching?  The BQ76952 supports clock stretching, and if the MCU paired with it does not, this can cause communication issues.  Finally, the BQ76952 has a Software Development Guide that you may find helpful.  I will link it here: BQ769x2 Software Development Guide (Rev. B) (ti.com).

For question 2, could you please send me the portion of your schematic showing how the cells are connected to the BQ76952?  Since you have 12S cells instead of 16S cells connected, ensure that you have the Vcell Mode register configured correctly to accommodate for this.  

I am going to attach a link to an FAQ discussing cell connection as well for your consideration.  Here is the link: (+) [FAQ] BQ76952: Connecting battery cells to the BQ769x2 family of monitors - Power management forum - Power management - TI E2E support forums.

Best,

Andria

Hello Andria,

Thx for the quick response.

I'm using BQ76952 AFE and not BQ76952EVM( I assume it's development board). MCU does support clock stretching. Here I'm attaching the part of schematic to show the cell connections with BQ76952.

Few more points,

1. I don't have the the external emulator with which I could read-write with the AFE.

2. I'm able to read the voltage using direct command irrespective of whether i configure the AFE or not(was able to read with disabling configuration as well). The value for the VCell that I have configured with is 0x000F, because 0x0000 is for 16 cells. Is it the right configuration? 

https://training.ti.com/microcontroller-programming-bq769x2-battery-monitor-family?context=1134734-1139259-1147303-1148694

The above link from ti training, talks about the software configuration of MCU for AFE BQ76952. I'm following the same. 

Let me know if there's anything that I'm missing with configuration. 

Hi Shashidhar,

The Vcell Mode value of 0x000F is incorrect.  The actual value should be 0x87FF.  I will attach a screenshot below from BQStudio showing which bits to set HIGH for your 12S cell configuration.  (HIGH bits are in red.)

For more information on Vcell mode, please see Section 13.3.2.19 Settings:Configuration:Vcell Mode in the Technical Reference Manual.  I will link it here: BQ76952 Technical Reference Manual (Rev. B) (ti.com).

Although I cannot see the input filter component values you selected, the cell connections to the BQ76952 look correct.

Best,

Andria

Hi Andria,

Have done the configuration. Was able to configure, read & write the RAM registers. I've got EV2300 using which I was able to ensure data written to RAM registers from MCU. The values read for cells from MCU very well matches with the same from EV2300 emulator connecting AFE to PC over USB. Here I have attached the snaps showing configuration, voltage of cells. It would be great if you can take a look at it and let me know where I went wrong.

I have 2 AFEs with me. The voltages measured from the cells from both AFE are correct for first 10 cells and invalid for 11th and 12th cells(Though I see 0 from 12th cell, I'm referring cell16 for the cell12). This issue still persists. 

Hello Shashidhar,

Andria is on vacations today, she will be returning tomorrow and may be able to further help.

I assume you mean the EV2400. The EV2300 does not support the BQ76952. It would be useful if you could share the .gg file itself so we can analyze it more carefully.

Could you share the .gg file?

Best Regards,

Luis Hernandez Salomon

Hello Luis,

The emulator that I used is EV2300 only. It seems to read registers from AFE and doesn't support write for BQ76952. I'll need little time to get the .gg file as the device is not with me now. As of now I'm able to measure first 11 cells out of 12 properly and I'm able to get some voltage from 16th cell which is not accurate(3.0v in place of 3.3V is received). Any suggestions/thoughts towards why is it inaccurate? and Is 16th cell reading the 12th cell voltage?(Note: For the cell voltage, I was testing with power supply before, this is the result from battery pack connected replacing power supply)

Hi Shashidar,

I am happy to hear that part of your original issue has been addressed.  As Luis stated, the EV2300 does not support the BQ76952.  This will cause problems, so I highly recommend that you obtain an EV2400.  

I am looking forward to seeing your gg.csv file when you have it!

Best,

Andria