BQ77908A Stand-Alone Multi-Cell Li-Ion/Li-Polymer Precision Protector |

This product has been released to the market and is available for purchase. For some products, newer alternatives may be available.
Stand-Alone Multi-Cell Li-Ion/Li-Polymer Precision Protector


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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


  • 4-, 5-, 6-, 7-, or 8-Series Cell Protection
  • Individual Cell-Voltage Monitoring
  • Low-Side NMOS FET Drive for Charge and Discharge Control
  • Compatible With 1-mΩ Current-Sense Resistor
  • Supply-Voltage Range From 5.6 V to 40 V
  • Integrated 3.3-V Micro-Power LDO Regulator
  • Low Supply Current
    • Normal Mode: 50 µA, Typical
    • Shutdown Mode, LDO OFF: 5 µA, Typical
  • 38-Pin TSSOP Package
  • Internal 50-mA Automatic Cell Balancing

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Part number Order Function Number of series cells (Min) Number of series cells (Max) Communication interface Features Typical operating current (Typ) (uA) Rating Vin (Max) (V) Package Group Approx. price (US$)
BQ77908A Order now Protection     4     8     No Communication     Low-Side NCH CHG/DSG FET Drive     5     Catalog     50     TSSOP | 38     5.06 | 1ku