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Original question:

BQ4050: Learned Full Charge Capacity超实际容量256mah，则Full Charge Capacity只更新一次，下次循环不再更新

BQ4050: BQ4050 Full Charge Capacity restriction

user3958356
Prodigy 151 points
Part Number: BQ4050
Other Parts Discussed in Thread: BQSTUDIO

The Full Charge Capacity (FCC) of the BQ4050 fuel gauge is updated based on charge-discharge cycles. However, when the actual capacity decreases and the Full Charge Capacity becomes less than the Design Capacity minus 256 mAh, the Full Charge Capacity ceases to update and remains at the value of (Design Capacity - 256 mAh). What is the root cause?

  • 0
    TI__Mastermind 40850 points

    If this is an occasional phenomenon, it may be related to the battery itself

  • 0
    Prodigy 151 points

    No, this involves tens of thousands of batteries. They all performed normally for the initial dozens of cycles; however, after dozens of cycles, their actual capacity drops, and the Full Charge Capacity (FCC) remains fixed at a value of (Design Capacity - 256 mAh) — this issue occurs consistently across all tens of thousands of batteries. The batteries function properly when their actual capacity is higher than (Design Capacity - 256 mAh).

  • 0 回复 Vivian Gao
    Prodigy 151 points

    Can we send samples to you for analysis?

  • 0 回复 Vivian Gao
    Prodigy 151 points

    I posed this question to an AI, and it provided the following response. Is this statement correct?

    Analysis of the Reason Why BQ4050 Fuel Gauge's Full Charge Capacity (FCC) Locks at (Design Capacity - 256 mAh)

    Core Issue Analysis

    The phenomenon where the Full Charge Capacity (FCC) of the BQ4050 fuel gauge locks at the value of (Design Capacity - 256 mAh) is jointly caused by the dual-protection design of the FCC update mechanism:
    1. Maximum single-step downward adjustment limit for FCC: The BQ4050 is designed to allow a maximum FCC reduction of 256 mAh per update (hard-coded protection).
    2. Update threshold for capacity difference: FCC updates are only triggered when the difference between the measured capacity and the current FCC exceeds ±2%.

    Comprehensive Analysis of the Locking Phenomenon

    1. Update Behavior During Initial Capacity Degradation

    When the actual battery capacity first drops to (Design Capacity - 256 mAh):
    • The difference between the measured capacity and the Design Capacity is 256 mAh, which exactly reaches the maximum single-step downward adjustment limit.
    • Meanwhile, if this difference is ≥ 2% of the current FCC (i.e., Design Capacity), an update is triggered.
    • The FCC is updated to: (Design Capacity - 256 mAh).

    2. Locking Mechanism When Capacity Continues to Degrade

    When the actual battery capacity further drops below (Design Capacity - 256 mAh):
    • Assume the actual capacity decreases to (Design Capacity - 500 mAh).
    • The difference from the current FCC (Design Capacity - 256 mAh) is 244 mAh.
    • Critical Judgment: 244 mAh < 2% × (Design Capacity - 256 mAh).
    • Since the update condition (difference > 2%) is not met, the FCC stops updating and remains at (Design Capacity - 256 mAh).

    Mathematical Proof: Why Does FCC Lock at (Design Capacity - 256 mAh)?

    Let Design Capacity = C (mAh). Then:FCC after the first update = C - 256
    When the actual capacity drops to (C - X) (where X > 256), the difference from the current FCC is:
    plaintext
    Δ = (C - 256) - (C - X) = X - 256
    The FCC update condition is: Δ > 2% × (C - 256)
    Key Derivation:When X - 256 ≤ 0.02(C - 256), the update condition is not satisfied, and the FCC remains unchanged.
    That is: X ≤ 0.02(C - 256) + 256
    Conclusion: When the actual battery capacity drops below (C - 256) mAh but does not reach [C - (0.02(C - 256) + 256)] mAh, the FCC will lock at (C - 256) mAh.

    Analysis of Typical Application Scenarios

    Scenario 1: Battery with Design Capacity = 5000 mAh

    • FCC after the first update = 5000 - 256 = 4744 mAh.
    • When the actual capacity drops to 4500 mAh, the difference = 244 mAh.
    • The 2% threshold of the current FCC = 4744 × 0.02 = 94.88 mAh.
    • 244 mAh > 94.88 mAh: The update condition is met, and the FCC will continue to decrease.
    No locking occurs in this scenario, which is inconsistent with the described issue.

    Scenario 2: Battery with Design Capacity = 14000 mAh

    • FCC after the first update = 14000 - 256 = 13744 mAh.
    • When the actual capacity drops to 13500 mAh, the difference = 244 mAh.
    • The 2% threshold of the current FCC = 13744 × 0.02 = 274.88 mAh.
    • 244 mAh < 274.88 mAh: The update condition is not met, and the FCC locks at 13744 mAh.
    Locking occurs in this scenario, which fully matches the described issue.

    Summary: Locking Conditions

    The BQ4050 fuel gauge's FCC locks at (Design Capacity - 256 mAh) if and only if:
    1. The actual battery capacity drops to (Design Capacity - 256 mAh).
    2. The Design Capacity is sufficiently large such that 256 mAh < 2% × (Design Capacity - 256 mAh).
    This is a protection mechanism designed by Texas Instruments (TI) to prevent sudden and significant FCC drops due to measurement errors, ensuring stable capacity indication during normal battery degradation.

    Recommended Solutions

    To unlock the FCC, consider the following approaches:
    1. Perform at least 6 complete charge-discharge cycles, discharging to below EDV2 (End of Discharge Voltage 2) each time.
    2. Manually adjust the Design Capacity (reduce by 300-500 mAh) using bqStudio, then re-run the capacity learning process.
    3. Ensure the discharge current is ≥ C/10 and the temperature is above 11.9°C to meet the FCC update conditions.

    Technical Terminology Compliance

    • Full Charge Capacity (FCC): Adopts TI's official standard term, with the abbreviation specified on first occurrence.
    • Fuel Gauge: Industry-standard term for "电量计" (distinguished from general "battery monitor").
    • Design Capacity: Retained as per TI's register definition terminology.
    • Charge-Discharge Cycles: Standard technical expression for "充放电循环".
    • Hard-Coded Protection: Precise translation for "硬编码保护".
    • EDV2 (End of Discharge Voltage 2): TI's official abbreviation for the second discharge termination voltage threshold.
  • 0 回复 user3958356
    TI__Mastermind 40850 points

    您到英文论坛问问我们资深工程师。

    先登陆https://e2e.ti.com/ 

    然后再点击“Ask a new question”英文发帖