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BQ40Z80: Learning Mode hardware setup

Krassi Atanassov
Prodigy 10 points
Part Number: BQ40Z80

Tool/software:

Hey,

I have built a custom pcb with bq40z80 and trying to succesfully execute the learning mode.
In section 4.2 of the slua848.pdf i have found very detailed guide of how to setup the various
registers, but when it comes to the hardware configuration, there is only this:

Discharge the battery until the voltage at the top of stack reaches the Term Voltage.

or

Charge Battery to Full

How do you do in practical term while allowing the chip firmware to observe the process properly?

I assume the guide expect everyone to use the EVAL board, so charge/discharge could be:

1. Dummy load(static) or CC/CV bench power supply to PACK+ and PACK- ?

2. As above, but between BAT+ and BMS GND ?

3. As above, but skipping the sense resistor, so BAT+ and BAT- ?

As i can read PACK, BATT and individual cells voltage, plus total and individual cells current, I assume

all those measurements are important for the learning process as well, so only option1 is viable, right ?

But section 4.2.1 calls for GAUGE_EN = 1, FET_EN=0 and RESET, so high side bidirection switch is off
during the learning process, so this will require to short PACK+ and BAT+ during the whole process ?

Thank you!

  • 0
    TI__Mastermind 37761 points

    Hello Krassi,

    That is correct option1 is viable. I am not sure what document you are referring to when you say section 4.2.1 but to complete the learning cycle the CHG FET and DSG FET should be on, so FET_EN should equal 1.

    Regards,

    Adrian

  • 0 in reply to Adrian
    Prodigy 10 points

    Hi Adrian,

    Thanks for your reply! Yes, i mean the learning guide document here:

    https://www.ti.com/lit/an/slua848/slua848.pdf

    page 6, section 4.2.1 says:

    Before beginning the discharge, turn on the charge and discharge FETs by sending command 0x22, or
by sending the CHG_FET_TOGGLE and DSG_FET_TOGGLE commands until both the CHG and
DSG bits are shown as red in the Bit Registers.

    but FET_EN bit is mutually exclusive with CHG_FET_TOGGLE and DSG_FET_TOGGLE bits while in Manufacturing Mode.

    Also those get disabled after reset as Unseal status and Manufacturing mode is cleared on Reset command.

    So i have found the only way to enter learning mode is to use FET_EN bit + GAUGE_EN and Reset, that sometimes leave the path from PACK+ to BAT+ open.

    Is there anyway to skip learning mode altogether in order to do electrical/functional testing on a new PCB ? Maybe like a standard golden file for 5S 4000 to 5000 mAh LiOn cells ?

    Thank you!

    Krassi

  • 0 in reply to Krassi Atanassov
    TI__Mastermind 37761 points

    Hello Krassi,

    Unfortunately, it is important to complete the learning cycle to ensure proper operation of the gauge. However, depending on what type of test you need to do, the learning cycle can happen after. What electrical/functional testing were you needing to do?

    Regards,

    Adrian

  • 0 in reply to Adrian
    Prodigy 10 points

    Hi Adrian,

    In Manufacture test mode, the MOSFETs seems to have constant DC on their gates. Also seems to be the case during learning cycle. But i assume after succesful learning cycle, the chip will feed variable duty PWM to the charging mosfet gate to control current ? Is there a way to test this ? Or just go with blind trust ? In my view so many things can go wrong - register values, bad soldering of the BMS chip, mosfets wiring, etc.

    Another thing that is difficult to test how power on/off of the BMS would work together with other modules in my system. It seems almost impossible to test/play with that before the learning cycle.

    Thank you!

  • +1 in reply to Krassi Atanassov
    TI__Mastermind 37761 points

    Hello Krassi,

    The gauge does not control the charging current through the battery. This will be done by the charger IC. The gauge can only control the FETs to turn on or off. The learning cycle purpose is to train the gauge on reporting an accurate SOC reading for the battery by performing discharge and charge tests. I think it should be fine to perform your electrical/functional testing before performing the learning cycle.

    Regards,

    Adrian