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Device not entering into Precharge mode

MounishPatel Seetha
Intellectual 795 points
Part Number: BQ76952

Hi, 

I have set PreCharge StartVoltage to 3600mv

PreCharge StopVoltage to 3900mv

PreChargeTimeout is left as default

all Cells are around 3700mV  butPrecharge FET is not turned what all registers need to be set?,

Not: I have mastered Dsg and Chg FETs ( and have a good idea of device, simply nt a beginner)

Please help

  • 0
    TI__Guru* 81035 points

    Hi Mounish,

    Do you have a log file you can share? The Battery Status register will show when precharge mode is occurring. It would also be good to see the register settings (.gg.csv file).

    When measuring the PCHG pin, it should be measuring a voltage below the battery (or pack) voltage to turn on the PFET. See the datasheet for the drive voltage levels.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 795 points

    Hi matt, I dont have a log file

    I have already checked Battery Status register,Device is not entering into Precharge mode,

    1.I saw in FET status register that Chg FET and DSG FET are being turned on but PChg and Pdsg Fets are off

    2. PChg pin Voltage is 0.005V lessthan Pack Voltage (B+), is it ok? Please find schematic

  • 0 in reply to MounishPatel Seetha
    TI__Guru* 81035 points

    The PCHG voltage measurement looks like the PCHG FET is off. Can you collect a log file so we can see all of the cell voltages and status registers? Can you also share the register settings for the device?

  • 0 in reply to Matt Sunna
    Intellectual 795 points

    Hi Matt , I am not using TI's BMS software , i coded device with another MCU

    following are cells Voltages (ignore minimumCellV) its  coding mistake. but CellMode register is set

    Precharge Start Voltage Register(0x930A)----------> 0xE10

    Precharge Stop Voltage Register(0x930C)----------> 0xF3C

    Enable protections A (0x9261)--------------------------> 0xFF

    Enable protections B (0x9262)-------------------------->0xF7

    Enable protections C //PTO enabled(0x9263)------->0x76

    FET Options (0x9308)-------------------------------------->0x1F

    PreDischarge Time out (0x930E)------------------------>200

    PreDischarge Stop Delta------------------------> left default

    charge current threshold (0x9312)----------------->0x0005

    Autonomous mode //Mfg status Init (0x9343)--------->0x0010

    For Autonomus Balancing(0x9335)-------------------->0x0F

    LD Active  time (0x92B4)-------------------------------->0x14

    subCommand(0x009A); //Disable sleep sub command
    subCommand(0x008A); //Pre-Charge Timeout Recovery

    Disable sleep mode (0x9234)----------------------->0x2882

    DA configuration register (0x9303)----------------->0x07

    are these good enough?

  • 0 in reply to MounishPatel Seetha
    TI__Guru* 81035 points

    Hi Mounish,

    Can you apply a charge current? The settings look okay.

  • 0 in reply to Matt Sunna
    Intellectual 795 points

    1.Finally device is entering into precharge mode when Iset Precharge start voltage to 3.8 and Precharge Stop Voltage to 3.9. I guess this not how it is supposed to work right?

    2. One more doubt is, will device be in predischarge mode always when load is removed? 

  • +1 in reply to MounishPatel Seetha
    TI__Guru* 81035 points

    Hi Mounish,

    I think this makes sense according to the TRM description for pre-charge start conditions: 

    Predischarge mode is only activated when the device first enables the discharge FET. If the load is removed after the discharge FET is already activated, it will not go into predischarge mode.

    Best regards,

    Matt