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BQ34Z100-G1: Learning Cycle only works with very small Flash Update Ok Cell

Gustaf Falk Olson58
Prodigy 610 points
Part Number: BQ34Z100-G1

Hi,

In the following forum post it was suggested to change the Flash Update Ok Cell to 999mV for a NiMH.battery: https://e2e.ti.com/support/power_management/battery_management/f/180/p/491414/1794498

This is a large discrepancy from the default 2800mVolt. In a setup with a 10s1p NiMH-battery where the chemical ID incidentally was the same, 6100, we could calculate from the formula given in the datasheet upon calibration of the voltage Divider value: Flash Update Ok Cell = 800m*10*5000/17583 = 2275mV. However, with these values Update Status and Max Error don't change as expected during the learning cycle. When setting Flash Update Ok Cell to 999mV, however, it appears to work.

Two questions:

1. The voltage divider value after calibration is 17583 as compared to the calculated 15740. Is this difference prohibitively large?

2. With Flash Update Ok Cell  at only 999mV what will be the minimum voltage for a flash update?

Thanks in advance,

Gustaf

 

  • 0
    TI__Mastermind 25955 points
    Hi Gustaf,

    The formula and 2800 mV guidance with respect to Flash Update OK Cell is based on a Li-Ion chemistry.

    For NiMH/NiCD chemistries, please use a value between 800-1000 mV.

    For Lead Acid, please use a value between 1000-1200 mV.

    1. The voltage divider does increase after calibration. This value is no prohibitively large.

    2. To determine what the minimum voltage for a flash update is, please test empirically by setting a value at the top of the above given ranges per chemistry. In your first sweep of range, decrement by 50 mV and test to see if a value is written to flash. Use the first failed write voltage value as your new upper bound and reduce the step size to 10 mV. Repeat again at 1 mV if this resolution is desired.

    Sincerely,
    Bryan Kahler