BQ20Z655 Datasheet, PDF (16/23 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE AND PROTECTION ENABLED WITH IMPEDANCE TRACK

bq20z655
SLUSAH8 – APRIL 2011
CONFIGURATION
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Oscillator Function
The bq20z655 fully integrates the system oscillators therefore, no external components are required for this
feature.
System Present Operation
The bq20z655 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 enters normal operating mode. When the pack is
removed from the system and the PRES input is high, the bq20z655 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 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 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 continuously integrates the signal over
time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq20z655 updates the individual series cell voltages at one second intervals. The internal ADC of the
bq20z655 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 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 can exit sleep mode, if enabled, by the presence of a programmable level of current signal across
SRP and SRN.
Auto Calibration
The bq20z655 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for
maximum charge measurement accuracy. The bq20z655 performs auto-calibration when the SMBus lines stay
low continuously for a minimum of a programmable amount of time.
Temperature
The bq20z655 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 can be configured to use the internal temperature sensor or up to 2 external
temperature sensors.
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