BQ20Z655-R1_13 Datasheet, PDF (16/25 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE AND PROTECTION ENABLED WITH IMPEDANCE TRACK™

bq20z655-R1
SLUSAN9 – AUGUST 2011
CONFIGURATION
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Oscillator Function
The bq20z655-R1 fully integrates the system oscillators therefore, no external components are required for this
feature.
System Present Operation
The bq20z655-R1 periodically verifies the PRES pin and detects that the battery is present in the system via a
low state on a PRES input. When this occurs, the bq20z655-R1 enters normal operating mode. When the pack is
removed from the system and the PRES input is high, the bq20z655-R1 enters the battery-removed state,
disabling the charge, discharge, and ZVCHG FETs. The PRES input is ignored and can be left floating when
non-removal mode is set in the data flash.
BATTERY PARAMETER MEASUREMENTS
The bq20z655-R1 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 bq20z655-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 bq20z655-R1 continuously integrates the signal
over time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq20z655-R1 updates the individual series cell voltages at one second intervals. The internal ADC of the
bq20z655-R1 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 bq20z655-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 bq20z655-R1 can exit sleep mode, if enabled, by the presence of a programmable level of current signal
across SRP and SRN.
Auto Calibration
The bq20z655-R1 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for
maximum charge measurement accuracy. The bq20z655-R1 performs auto-calibration when the SMBus lines
stay low continuously for a minimum of a programmable amount of time.
Temperature
The bq20z655-R1 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 bq20z655-R1 can be configured to use the internal temperature sensor or up to
2 external temperature sensors.
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