Battery Management Unit / Gas Gauge

STAR2011 is an ultra-low power Battery Management Unit (BMU) designed to provide voltage and charge monitoring of a battery. The BMU is designed to monitor the voltage and current levels of a battery cell, using two delta-sigma ADC's. A 10b ADC with a single-ended input voltage range of 0 to 250mV is used to measure the battery voltage through an internal voltage-divider from the external battery voltage. A 10b ADC with single-ended input voltage range of -250mV to 250mV is used to measure the voltage across a resistor which is placed in series with the battery cell for current measurement.

Power-on-reset (POR) and Low-voltage-detect (LVD) circuits are designed to produce digital control signals/flags to indicated the state of the battery voltage when the battery is close to it's end of life (<0.8V) when the ADC measurements of the battery are unreliable or invalid. POR, with it's threshold set nominally at 0.6V, provides the power-on-reset function as well as indicates that the battery is in the 'dead zone'. The LVD circuit is designed to have 2 thresholds: LVD1 and LVD2. LVD1 is set nominally at 0.6V which indicates that the battery is in the 'danger-zone' whereas LVD2 is set nominally at 0.8V which indicates that the battery is in the 'safe-zone'. Test time programmability of the POR, LVD1, LVD2 are provided for users to fine-adjust the threshold levels.

An internal clock generator provides a 32.768KHz master clock for the ADCs, and can also be used for the SoC that uses this BMU macro. The actual clock frequency can be factory calibrated to within +/-1% accuracy; the calibration bits are then stored into OTP which can be auto-loaded in the field. For hearing-aid systems, STAR2011 acts as a smart power-control-unit which can generate control signals to enable various sub-blocks of the overall system to power on/off safely for different states of charge in the battery.