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BQ24780SEVM-583: Learn mode

Part Number: BQ24780SEVM-583

Hi expert,

 I connect Vsys to a CC mode E-load and connect Vbat to a power source. When I enable the learn mode by  battery management studio. The Vsys is still equal to Vadaptor.It seem didn't go into learn mode.  After  reading register, the REG0x12[5]=0. How to enable the learn mode in EVM?

  • Dylan,

    What is the voltage on BAT from the power source? It must higher than the battery depletion threshold set in register 0x3BH in order to enter LEARN cycle.
  • Hi Jeff,
    The voltage on BAT from the power source is 10V, the battery depletion threshold set in register 0x3BH is 59.19%. The charge voltage set in register REG0x15 is 12592mV. The detail register configuration is shown in attached picture above.
  • Hi Dylan,

    I was able to get Learn Mode working on the EVM with the following procedure:

    1.  With board unpowered, place jumper on JP6, remove all other jumpers (JP1-5)

    2.  Apply 10V CV mode source at BAT with 100,000 uF capacitor to simulate battery.

    3.  Apply 1A sink at SYS (e-load in CC mode)

        SYS is at 10V, BAT terminal supplying 1A

    3.  Apply 20V CV mode source at VIN

        SYS is at 20V, BIN supplying 1 A, BAT terminal drops to negligible current

    4.  Write 0x8128 into register 0x12 (Charge Option 0) -- all other registers were left at POR default

         This disables watchdog timer and sets the Learn Mode enable

        V_SYS drops from 20V to 10V, BAT terminal is supplying 1A, VIN is at 20V but supplying no current

    5.  Write 0x8108 into register 0x12

        This disables learn mode

        V_SYS rises from 10V to 20V, Bat terminal is negligible current, VIN supplying 1A

    Here is a capture of step 4:

    I also copied your settings from the screen capture above and was able to toggle in and out of Learn Mode.

    I noticed, however, when I was copying your settings that the bit 11 of Charge Option 3 register is cleared, indicating that no adapter is present.  I also saw no mention of adapter/adapter voltage in your description.  The functionality of the Learn Mode is to disconnect the adapter and force SYS to pull current from BATT even if VIN is present, so I believe you will need an adapter in order to see the effect of enabling the mode.

    Can you retry with a 20V adapter voltage and see if you are able to toggle in and out of Learn mode?  If Learn mode is still failing, can you capture V_IN, V_BATT and V_SYS and, if you have current probe, I_BATT, after writing 0x8108 (or similar) into register 0x12?    You can set up a high-to-low trigger on V_SYS at around 15V.  If the device is attempting to transition between VIN and BATT and for some reason the transition fails, the voltage should still temporarily transition from 20V to 10V on VSYS and hopefully you can capture the attempt.

    Regards,

    Steve

  • Hi Steve,

    Thank you for your detailed reply. That's very helpful. The issue is solved.

    Regards,

    Dylan