BQ20Z90_07 Datasheet, PDF (10/27 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE ENABLED WITH IMPEDANCE TRACK™ TECHNOLOGY FOR USE WITH THE bq29330

bq20z90
SLUS662A – DECEMBER 2005 – REVISED JUNE 2006
www.ti.com
FEATURE SET (continued)
BATTERY PARAMETER MEASUREMENTS
The bq20z90 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 bq20z90 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 bq20z90 continuously integrates the signal over
time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq20z90 updates the individual series cell voltages through the bq29330 at one second intervals. The
bq20z90 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 bq20z90. The internal ADC of the bq20z90
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 bq20z90 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 bq20z90 can exit sleep mode, if enabled, by the presence of a programmable level of current signal across
SRP and SRN.
Auto Calibration
The bq20z90 provides an auto-calibration feature to cancel the voltage offset error across SRP and SRN for
maximum charge measurement accuracy. The bq20z90 performs auto-calibration when the SMBus lines stay
low continuously for a minimum of a programmable amount of time.
Temperature
The bq20z90 TS1 and TS2 inputs, in conjunction with two identical NTC thermistors (default are Semitec
103AT), measure the battery environmental temperature. The bq20z90 can also be configured to use its internal
temperature sensor.
COMMUNICATIONS
The bq20z90 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS
specification.
SMBus On and Off State
The bq20z90 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.
SBS Cmd Mode Name
0x00
0x01
R/W ManufacturerAccess
R/W RemainingCapacityAlarm
0x02
R/W RemainingTimeAlarm
Table 1. SBS COMMANDS
Format
hex
unsigned int
Size in
Bytes
2
2
Min
Value
0x0000
0
unsigned int
2
0
Max
Value
0xffff
65535
65535
Default Value
—
300
10
Unit
mAh or
10mWh
min
10
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