BQ20Z70_17 Datasheet, PDF (8/17 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE ENABLED WITH IMPEDANCE TRACK TECHNOLOGY FOR USE WITH THE bq29330

bq20z70
Not Recommended For New Designs
SLUS686B – NOVEMBER 2005 – REVISED JULY 2007
www.ti.com
FEATURE SET (continued)
Power Modes
The bq20z70 supports 3 different power modes to reduce power consumption:
• In Normal Mode, the bq20z70 performs measurements, calculations, protection decisions and data updates
in 1 second intervals. Between these intervals, the bq20z70 is in a reduced power stage.
• In Sleep Mode, the bq20z70 performs measurements, calculations, protection decisions and data update in
adjustable time intervals. Between these intervals, the bq20z70 is in a reduced power stage. The bq20z70
has a wake function that enables exit from Sleep mode, when current flow or failure is detected.
• In Shutdown Mode the bq20z70 is completely disabled.
CONFIGURATION
Oscillator Function
The bq20z70 fully integrates the system oscillators. Therefore, the bq20z70 requires no external components for
this feature.
System Present Operation
The bq20z70 pulls the PU pin high periodically (1 s). Connect this pin to the PRES pin of the bq20z70 via a
resistor of approximately 5 kΩ. The bq20z70 measures the PRES input during the PU-active period to determine
its state. If PRES input is pulled to ground by external system, the bq20z70 detects this as system present.
BATTERY PARAMETER MEASUREMENTS
The bq20z70 uses an integrating delta-sigma analog-to-digital converter (ADC) for current measurement, and a
second delta-sigma ADC for individual cell and battery voltage, and temperature measurement.
Charge and Discharge Counting
The integrating delta-sigma ADC measures the charge/discharge flow of the battery by measuring the voltage
drop across a small-value sense resistor between the SR1 and SR2 pins. The integrating ADC measures bipolar
signals from -0.25 V to 0.25 V. The bq20z70 detects charge activity when V_SR = V_(SR1)-V_(SR2)is positive and
discharge activity when V_SR = V_(SR1)-V_(SR2) is negative. The bq20z70 continuously integrates the signal over
time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq20z70 updates the individual series cell voltages through the bq29330 at one second intervals. The
bq20z70 configures the bq29330 to connect the selected cell, cell offset, or bq29330 VREF to the CELL pin of
the bq29330, which is required to be connected to VIN of the bq20z70. The internal ADC of the bq20z70
measures the voltage, scales and calibrates it appropriately. This data is also used to calculate the impedance
of the cell for the Impedance Track™ gas-gauging.
Current
The bq20z70 uses the SRP and SRN inputs to measure and calculate the battery charge and discharge current
using a 5 mΩ to 20 mΩ typ. sense resistor.
Auto Calibration
The bq20z70 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for
maximum charge measurement accuracy. The bq20z70 performs auto-calibration when the SMBus lines stay
low continuously for a minimum of 5 s.
Temperature
The bq20z70 has an internal temperature sensor and 2 external temperature sensor inputs TS1 and TS2 used
in conjunction with two identical NTC thermistors (default are Semitec 103AT) to sense the battery enviromental
temperature. The bq20z70 can be configured to use internal or external temperature sensors.
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