BQ27750 Datasheet, PDF (20/34 Pages) Texas Instruments – Impedance Track Battery Gas Gauge and Protection Solution for 1-Series Cell Li-Ion Battery Packs

bq27750
SLUSCM7 – JUNE 2017
www.ti.com
7.4 Device Functional Modes
This device supports three modes, but the current consumption varies, based on firmware control of certain
functions and modes of operation:
• NORMAL mode: In this mode, the device performs measurements, calculations, protections, and data
updates every 250-ms intervals. Between these intervals, the device is operating in a reduced power stage to
minimize total average current consumption.
• SLEEP mode: In this mode, the device performs measurements, calculations, protections, and data updates
in adjustable time intervals. Between these intervals, the device is operating in a reduced power stage to
minimize total average current consumption.
• SHUTDOWN mode: The device is completely disabled.
7.4.1 Lifetime Logging Features
The device supports data logging of several key parameters for warranty and analysis:
• Maximum and Minimum Cell Temperature
• Maximum Current in CHARGE or DISCHARGE Mode
• Maximum and Minimum Cell Voltages
7.4.2 Configuration
The device supports accurate data measurements and data logging of several key parameters.
7.4.2.1 Coulomb Counting
The device uses an integrating delta-sigma analog-to-digital converter (ADC) for current measurement. The ADC
measures charge/discharge flow of the battery by measuring the voltage across a very small external sense
resistor. The integrating ADC measures a bipolar signal from a range of –100 mV to 100 mV, with a positive
value when V_(SRP) – V_(SRN), indicating charge current and a negative value indicating discharge current. The
integration method uses a continuous timer and internal counter, which has a rate of 0.65 nVh.
7.4.2.2 Cell Voltage Measurements
The bq27750 gas gauge measures the individual cell voltages at 250-ms intervals using an ADC. This measured
value is internally scaled for the ADC and is calibrated to reduce any errors due to offsets. This data is also used
for calculating the impedance of the individual cell for Impedance Track gas gauging.
7.4.2.3 Current Measurements
The current measurement is performed by measuring the voltage drop across the external sense resistor (1 mΩ
to 3 mΩ) and the polarity of the differential voltage determines if the cell is in the CHARGE or DISCHARGE
mode.
7.4.2.4 Auto Calibration
The auto-calibration feature helps to cancel any voltage offset across the SRP and SRN pins for accurate
measurement of the cell voltage, charge/discharge current, and thermistor temperature. The auto-calibration is
performed when there is no communication activity for a minimum of 5 s on the bus lines.
7.4.2.5 Temperature Measurements
This device has an internal sensor for on-die temperature measurements, and the ability to support external
temperature measurements via the external NTC on the TS1 pin. These two measurements are individually
enabled and configured.
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