The bq77PL900 is a five to ten series cell lithium-ion battery pack protector. The integrated I²C communications interface allows the bq77PL900 also to be as an analog front end (AFE) for a Host controller. Two LDOs, one 5 V/25 mA and one 3.3 V/25 mA, are also included and may be used to power a host controller or support circuitry.

The bq77PL900 integrates a voltage translation system to extract battery parameters such as individual cell voltages and charge/discharge current. Variables such as voltage protection thresholds and detection delay times can be programmed by using the internal EEPROM.

The bq77PL900 can act as a stand-alone self-contained battery protection system (stand-alone mode). It can alternatively be combined with a host microcontroller to offer fuel gauge or other battery management capabilities to the host system (host-control mode).

The bq77PL900 provides full safety protection for overvoltage, undervoltage, overcurrent in discharge, and short circuit in discharge conditions. When the EEPROM programmable safety thresholds are reached, the bq77PL900 turns off the FET drive autonomously. No external components are needed to configure the protection features.

The analog front end (AFE) outputs allow a host controller to observe individual cell voltages and charge/discharge currents. The host controller's analog-to-digital converter connects to the bq77PL900 to acquire these values.

Cell balancing can be performed autonomously, or the host controller can activate it individually via a cell bypass path integrated into the bq77PL900. Internal control registers accessible via the I²C interface configure this operation. The maximum balancing bypass current is set via an external series resistor and the internal FET-on resistance (typically 400 Ω). Optionally, external bypass cell balance FETs can be used for increased current capability.