Analog front end for 3 to 6 series lithium-ion cells

BQ76925 host-controlled analog front end (AFE) is part of a complete pack monitoring,balancing, and protection system for 3-, 4-, 5-, or 6-series cell li-ion and li-polymer batteries.The BQ76925 device allows a host controller to monitor individual cell voltages, pack current andtemperature easily. The Host may use this information to determine unsafe or faulty operatingconditions such as overvoltage, undervoltage, overtemperature, overcurrent, cell imbalance, stateof charge, and state of health conditions.

Cell input voltages are level-shifted, multiplexed, scaled, and output for measurement bya host ADC. A dedicated pin provides a low-drift calibrated reference voltage to enable accuratemeasurements.

The voltage across an external-sense resistor is amplified and output to a host ADC forboth charge and discharge current measurements. Two gain settings enable operation with a varietyof sense resistor values over a wide range of pack currents.

To enable temperature measurements by the host, the AFE provides a separate output pinfor biasing an external thermistor network. This output can be switched on and off under hostcontrol to minimize power consumption.

The BQ76925 device includes a comparator with a dynamically selectable threshold formonitoring current. The comparator result is driven through an open-drain output to alert the hostwhen the threshold is exceeded. This feature can be used to wake up the host on connection of theload, or to alert the host to a potential fault condition.

The BQ76925 device integrates cell balancing FETs that are fully controlled by the host.The balancing current is set by external resistors up to a maximum value of 50 mA. These same FETsmay be utilized in conjunction with cell voltage measurements to detect an open wire on a cellsense-line.

The host communicates with the AFE through an I2C interface. Apacket CRC may optionally be used to ensure robust operation. The device may be put into alow-current sleep mode through the I2C interface and awakened by pullingup the ALERT pin.)