BQ77908A

The bq77908A is a battery protection and cell balancing device intended for Li-Ion and Li-Polymer battery packs.

The bq77908A monitors 4- to 8-series individual cell voltages and provides fast-acting outputs that may be used to drive N-channel MOSFETs to interrupt the power path. Activation delays and recovery methods for safety conditions are fully programmable in non-volatile memory.

Automatic cell balancing is provided using internal 50-mA cell circuits. A robust balancing algorithm ensures optimum performance by maintaining all cell voltages in balance. Balancing may be configured to operate at all times, only during charge, or can be disabled completely.

Additional advanced safety features of the bq77908A include the ability to control split power-path MOSFETs, an open-cell sense-line detection mechanism, and the ability to detect an open or shorted external temperature sensor fault condition.

Programmable Protection Functions

• Wide range of programmable detection thresholds and delay times
• Configurable for multiple cell types and application requirements:
  • Cell overvoltage
  • Cell undervoltage
  • Pack discharge overcurrent
  • Pack discharge short circuit
  • Pack charge short-circuit current
• Variable gain (×1 or ×5) current-sense circuit
  • Compatible with a wide range of current-sense resistors (1-mΩ to 5-mΩ typical) sized for application requirements

Fixed Hardware Protection Functions

• Preset overtemperature protections
• Open-cell detection
• Open and shorted thermistor detection
• Brownout protection quickly shuts off FETs under low-battery conditions to minimize the risk of FET overheating