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Original question:

BQ76952: Autonomous Balancing in BQ76952

BQ76952: Design just as a battery monitor but don't want to include the charge/discharge mosfets

MK FX
Prodigy 10 points
Part Number: BQ76952

Tool/software:

Dear TI expert,

I am designing a Battery Monitoring Unit (BMU) for 16x LiFePO4 (LFP) 280Ah cells with balancing of 150mA per cell. Rated cell voltage = 3.2V, normal voltage range of each cell is 2.5V ~3.65V.

My question is can the BQ76952 be designed as a BMU that does NOT include the charge-discharge FET circuit (this immediately turns the PCB into a 14.4 kW system requiring power rails). The BQ76952 EVM SLUUC33A schematic fig5-11, pg43 indicate that the charge/discharge FETs are DNP, which is a sign that the charge/discharge FETs are optional in a BMU design. I also noted that the EVM implements the BQ771807DPJR OVP IC.

Q: Can the BQ76952 be implemented as a: 16-cell LFP load-balancer/monitoring protector AND fuel gauge ONLY (no charge/discharge). 

If FG is not a native function of the BQ76952, is there a reference design from TI for FG+protection based around the BQ76952 (or equivalent) for 100mAh/resolution at 50Hz sampling? Total pack capacity is 16x 280Ah = 4.5kAh @ 40 - 60V. 

  • +1
    TI__Prodigy 730 points

    Yes, the device can configured as a BMU that does NOT include the CHG / DSG protection FET circuit. There are some useful sections in the BQ769x2 Frequently Asked Questions document that should help you implement this.

    Section 1.6 describes how to connect unused pins. If not using protection FETS you should follow the recommendations for the following pins: PDSG, PCHG, DSG, CHG, LD, and CP1.

    You will also want to disable the Discharge and Charge FETs using the configuration registers, this is described in Section 2.12.

    As for the Fuel Gauging, the device doe not directly provide a State of Health (SOH) and State of Charge (SOC). But the data measured by the BQ769x2 can be passed to a microcontroller unit (MCU) which can perform the calculations for a gauging algorithm if desired. Section 1.5 describes this further.