BQ20Z75_08 Datasheet, PDF (12/20 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE AND PROTECTION-ENABLED IC WITH IMPEDANCE TRACK

bq20z75
SLUS723C – JULY 2007 – REVISED JULY 2008............................................................................................................................................................... www.ti.com
• In Sleep Mode, the bq20z75 performs measurements, calculations, protection decisions and data update in
adjustable time intervals. Between these intervals, the bq20z75 is in a reduced power stage. The bq20z75
has a wake function that enables exit from Sleep mode, when current flow or failure is detected.
• In Shutdown Mode the bq20z75 is completely disabled.
CONFIGURATION
Oscillator Function
The bq20z75 fully integrates the system oscillators. Therefore the bq20z75 requires no external components for
this feature.
System Present Operation
The bq20z75 checks the PRES pin periodically (1 s). Connect the PRES pin to TOUT with a 100kΩ resistor. If
PRES input is pulled to ground by external system host, the bq20z75 detects this as system present.
BATTERY PARAMETER MEASUREMENTS
The bq20z75 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 SRP and SRN pins. The integrating ADC measures bipolar
signals from –0.25 V to 0.25 V. The bq20z75 detects charge activity when V_SR = V_(SRP)–V_(SRN)is positive and
discharge activity when V_SR = V_(SRP)–V_(SRN) is negative. The bq20z75 continuously integrates the signal over
time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq20z75 updates the individual series cell voltages at one second intervals. The internal ADC of the
bq20z75 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 bq20z75 uses the GSRP and GSRN inputs to measure and calculate the battery charge and discharge
current using a 5 mΩ to 20 mΩ typ. sense resistor.
Auto Calibration
The bq20z75 provides an auto-calibration feature to cancel the voltage offset error across GSRN and GSRP for
maximum charge measurement accuracy. The bq20z75 performs auto-calibration when the SMBus lines stay
low continuously for a minimum of 5 s.
Temperature
The bq20z75 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 environmental
temperature. The bq20z75 can be configured to use internal or external temperature sensors.
COMMUNICATIONS
The bq20z75 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS
specification.
SMBus On and Off State
The bq20z75 detects an SMBus off state when SMBC and SMBD are logic-low for ≥ 2 seconds. Clearing this
state requires either SMBC or SMBD to transition high. Within 1 ms, the communication bus is available.
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