SBAA885 October   2026 BQ76907-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Passive Balancing Mechanism of BQ76907
    1. 2.1 Balancing Current Path
    2. 2.2 Balancing Current
    3. 2.3 Balancing Time Estimation
  6. 3Particularity of Supercapacitor Systems
    1. 3.1 ESR and Voltage Recovery Effect
    2. 3.2 Impact on Balancing Strategy
  7. 4Balancing Scheme Design
  8. 5Reference Algorithm Implementation and Example
    1. 5.1 Algorithm Flow and Pseudocode
    2. 5.2 Design Example
  9. 6Conclusion
  10. 7References

2.1 Balancing Current Path

The datasheet of BQ76907-Q1 indicates that the device supports host-controlled passive balancing, which can be initiated via subcommands, supporting simultaneous balancing of adjacent or non-adjacent cells.

Below is a simplified structural diagram of the 5-series supercapacitor in the external FET + resistor passive balancing scheme. This diagram expresses the balancing current path, not a complete schematic diagram.

Schematic Diagram of 5-Series Supercapacitor Balancing CircuitFigure 2-1 Schematic Diagram of 5-Series Supercapacitor Balancing Circuit

When the n-th string balancing is turned on, the current path is:

Equation 1. V C n → Q n → R n → V C n - 1

This means:

The balancing branch of Cell 5 discharges the energy of Cell 5 to the VC4 node

The balancing branch of Cell 4 discharges the energy of Cell 4 to the VC3 node

…

The balancing branch of Cell 1 returns the energy of Cell 1 to the VC0 node

This is a typical top-down passive discharge structure. The function of this structure is to reduce the energy stored in high-voltage cells, rather than transferring energy to low-voltage cells. This characteristic determines that passive balancing can only achieve a voltage reduction of high-voltage strings, but cannot directly increase the voltage of the lowest voltage string. Therefore, it will be reflected in tests as slow balancing speed and low efficiency.