BQ34Z651_15 Datasheet, PDF (18/29 Pages) Texas Instruments – SBS 1.1-Compliant Gas Gauge

bq34z651
SLUSAL7 – AUGUST 2011
CONFIGURATION
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Oscillator Function
The bq34z651 fully integrates the system oscillators; therefore, no external components are required for this
feature.
System Present Operation
The bq34z651 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 bq34z651 enters normal operating mode. When the pack is
removed from the system and the PRES input is high, the bq34z651 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 bq34z651 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 bq34z651 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 bq34z651 continuously integrates the signal over
time using an internal counter. The fundamental rate of the counter is 0.65 nVh.
Voltage
The bq34z651 updates the individual series cell voltages at one second intervals. The internal ADC of the
bq34z651 measures the voltage, and 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 bq34z651 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 bq34z651 can exit sleep mode, if enabled, by the presence of a programmable level of current signal across
SRP and SRN.
Auto Calibration
The bq34z651 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for
maximum charge measurement accuracy. The bq34z651 performs auto-calibration when the SMBus lines stay
low continuously for a minimum of a programmable amount of time.
Temperature
The bq34z651 has an internal temperature sensor and two external temperature sensor inputs, TS1 and TS2,
used in conjunction with two identical NTC thermistors (default is Semitec 103AT) to sense the battery
environmental temperature. The bq34z651 can be configured to use the internal temperature sensor or up to two
external temperature sensors.
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