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BQ76952: 32S SCHEMATIC

Govinda Giri
Prodigy 95 points
Part Number: BQ76952
Other Parts Discussed in Thread: UCC27523

 Hi Expert

Greetings of the day!

 Last Thread:  https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1213431/bq76952-32s-with-low-side-switching-solution/4595910#4595910

As per the Discussion in the last thread with Luis, I'm attaching a schematic for 32S for validation purposes. Kindly help.

Upper side AFE 

Lower side AFE with Low side Switching

Do reach out to me in case of any queries!

Regards
Govinda

  • 0
    TI__Expert 3245 points

    HI Govinda, 

    Would you mind sharing a pdf version of the document or a higher resolution picture? The attached images are difficult to read, much appreciated!

    Best, 

    -Luis Torres

  • 0 in reply to Luis Torres
    Prodigy 95 points

    Hi Luis 

    As per discussion, here is the schematic in PDF format.

    BMS_24S_Org.pdf

    Regards
    Govinda

  • +1 in reply to Govinda Giri
    TI__Expert 3245 points

    Hi Govinda, 

    Please see the following suggestions. 

    1. For the FET driver logic, using a NAND gate will not work in this case. To achieve active-low behavior, we recommend using a NOR gate so that either AFE is able to shut off the FET's. 

    Active-low FET drive: 

    • Case1:When DSG FET state low and CHG FET state low,  FETs drive high (FETs on)
    • Case2:When DSG FET state high and CHG FET state low,  FETs drive low (FETs off)
    • Case3:When DSG FET state low and CHG FET state high, FETs drive low (FETs off)
    • Case4:When both DSG and CHG FET drive high, FETs drive low (FETs off)

    This behavior is for active-low FET drive. If active-high behavior is desired you can then use an AND gate for this logic. 

    2. We recommend using a reasonably sized resistor (0ohm or larger) between the UCC27523 driver outputs OUTA and OUTB to DSG and CHG pins respectively. (i.e 0ohm between OUTA and CHG pin ; 0ohm between OUTB and DSG pin) 

    3. Found incomplete connection to NFET Q18 source.  

    4.Can you help explain what customer is trying to do with this circuit using SHUT_U and SHUT_B?

    5. Please note that the PDSG pin is only able to sink current. Using this pin to power the optocoupler may not work as intended.

    6. Please refer to this app note Using Low-Side FETs with the BQ769x2 Battery Monitor Family for any additional considerations: https://www.ti.com/lit/an/sluaa84a/sluaa84a.pdf

    Please let me know if any additional questions/clarifications. 

    Best, 

    -Luis Torres