BQ20Z40-R1 Datasheet, PDF (10/16 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE ENABLED WITH IMPEDANCE TRACK™ TECHNOLOGY FOR USE WITH THE bq29330

bq20z40-R1
SLUS993 – DECEMBER 2009
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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 bq20z40-R1 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 bq20z40-R1 continuously integrates the signal
over time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq20z40-R1 updates the individual series cell voltages through the bq29330 at one second intervals. The
bq20z40-R1 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 bq20z40-R1. The internal ADC of the
bq20z40-R1 measures the voltage, scales it, and calibrates itself appropriately. This data is also used to
calculate the impedance of the cell for the Impedance Track™ gas-gauging.
Current
The bq20z40-R1 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.
Wake Function
The bq20z40-R1 can exit sleep mode, if enabled, by the presence of a programmable level of current signal
across SRP and SRN.
Auto Calibration
The bq20z40-R1 provides an auto-calibration feature to cancel the voltage offset error across SRP and SRN for
maximum charge measurement accuracy. The bq20z40-R1 performs auto-calibration when the SMBus lines stay
low continuously for a minimum of a programmable amount of time.
Temperature
The bq20z40-R1 has an internal temperature sensor and inputs for 2 external temperature sensors, TS1 and
TS2, used in conjunction with two identical NTC thermistors (default are Semitec 103AT) to sense the battery
environmental temperature. The bq20z40-R1 can be configured to use internal, or up to 2 external temperature
sensors.
COMMUNICATIONS
The bq20z40-R1 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS
specification.
SMBus On and Off State
The bq20z40-R1 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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