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Original question:

BQ40Z80: Some questions about Impedance Track

BQ40Z60: Fast Qmax update feature

David Wikholm
Prodigy 30 points
Part Number: BQ40Z60

In my application, the battery pack will always be in a state of charging or discharging without relaxation. Therefore we want to use the Fast Qmax feature during normal use for most accurate gauging.

I have done many charge/discharge cycle testing with FAST_QMAX_FLD enabled, but I never get a Qmax update (meaning the QMAX register never flips to 1, Qmax values never update, and Qmax Cycle Count does not increment). Should I expect those things to happen with the Fast Qmax feature, or is that working behind the scenes? In my testing I only get an actual Qmax update when allowing the pack to relax after charging and discharging.

  • 0
    TI__Mastermind 42535 points

    Hi David,

    You need a min passed chg and a fully valid DOD taken from relaxation at one end to update Qmax using Fast Qmax. Under the below conditions fast qmax updates will not happen

    1. DOD < Fast Qmax End DOD
    2. Charge terminates in OCVFR
    3. Fast Qmax Update occurred on the preceding cycle
    4. No OCV measurement since previous Qmax update
    5. Fast Qmax Updates will be disqualified if there is more than 5% difference between the estimated and measured Depth of Discharge (DOD). The estimated DOD is calculated by estimating the open circuit voltage (OCV) by subtracting the calculated IR drop from the instantaneous voltage and interpolating DOD from a table providing DOD as a function of OCV. Calculated DOD is based on the Qmax Passed Q and starting DOD (taken during an OCV measurement at the top of charge) values