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BQ76942: Hardware and software configuration for 5S using BQ76942

Shashi Rai
Prodigy 120 points
Part Number: BQ76942
Other Parts Discussed in Thread: BQSTUDIO, BQ76952

Tool/software:

Hi, 

As I am working on a Li-Ion battery-based product design project and for the same i have chooses the BQ76942 as AFE.

The Battery has 5 series cells. 

Here I have a few queries: 

1) As given in datasheet example design (page no 69) for 7 series cell, we have shorted the terminals VC4 , VC5, VC6, VC7, VC8, VC9, and cell connected between the VC10-VC9, VC9-VC3, VC3-VC2, VC2-VC1 and VC1-VC0. Is it correct? Please review and comment if any.

Note: Ignore additional Provision connections for 4 series cell configuration in design (shorting provision of VC3 and VC4 through R44 and C14).

2) How many bits need to be enabled in VCELL_MODE configuration in BQstudio for 5 series cell according to the above circuit?

As per the reference document (Easy Configuration of BQ76942, BQ76952 Battery Monitors)  shows the example of 8 series cell and enables the bit 10, bit 9 , bit 6, bit 5, bit 4, bit 3, bit 2 and bit 1. 

While when I am doing the same for 5 cell configuration, the under-voltage protection triggers, Also on the home page of BQ studio voltage of cell 9 shows as 0V.

Kindly suggest for 5 cell configuration with the above circuit bit 9 of VCELL_MODE need to enable or not?

As per me understanding only bit 10, bit 4, bit 3, bit 2 and bit 1 needs to enable. bit 9 not required to enable in this case. Please suggest.

Link : https://www.ti.com/lit/ug/sluu446d/sluu446d.pdf?ts=1727091445897&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FEV2400

Thanks & Regards,

Shashikumar Rai

  • 0
    TI__Genius 17835 points

    Hello Shashikumar,

    1) The picture you tried to share is not showing up on my end. Do you mind sharing it again? Also, Section 16.6 Unused Pins in the BQ76942 Datasheet should also help in how to terminate unused pins such as the cell connections.

    2) Do you mind sharing your entire bqStudio (.gg) file? Also, the image of how you have your cells connected would help as well.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 120 points

    Hi Alexis,

    1) OK, I am sharing the PDF for the circuit. As I have referred the Section 16.6 Unused Pins.  Although I got the under voltage trigger and . Please review and suggest me on the same.

    BQ76942_CKT.pdf

    2) Ok I am Sharing the (.gg) file, Note I am on initial face of development, Here I have only enabled the CUV and COV, with VCELL_MODE settings.

    BQ studio - Home page image

    BQ studio - VCELL mode Register

    BQ Studio - (.gg) file

    BQ76942_5S cell configuration file.gg.csv

    our cell configuration is 5 series cell to achieve 16-21V with lithium ion cells.

    Thanks & Regards,

    Shashikumar Rai

  • 0 in reply to Shashi Rai
    TI__Genius 17835 points

    Hello Shashikumar,

    Thanks for sharing the pdf file showing the schematic and the bqStudio file and screenshot. Based on those documents, it looks like VCELL mode is setup correctly. Can you please share a screenshot showing the full screen of bqStudio when the fault occurs or the .gg file when the fault occurs? I did not see the fault on the current file you have shared.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 120 points

    Hello Alexis_H

    Thanks for confirming against the design files.

    The fault occurs when we configure the Vcell_Mode as per the example given in the  document "Easy Configuration of BQ76942/52 Battery Monitors (Rev. A)"

    Note the Example given for 8 series cell configuration.

    1 ) As per the document example: Fault occurs 

    2) As per my understanding: No Fault

    Please correct me which configuration is required against my design. 1 or 2 ?

    Thanks and Regards,

    Shashikumar Rai

  • +1 in reply to Shashi Rai
    TI__Genius 17835 points

    Hello Shashikumar,

    Thank you for pointing that out. The configuration for your design should be 2). The document’s picture of VCELL mode there is incorrect in reference to the 8S cell configuration from the EVM User Guide. Section 13.3.2.19 Settings:Configuration:Vcell Mode of the BQ76942 Technical Reference Manual gives more information on how VCELL mode should be configured. 

    Best Regards,
    Alexis