BQ20Z70 Datasheet, PDF (8/22 Pages) Texas Instruments – SBS 1.1-COMPLIANT GAS GAUGE ENABLED WITH IMPEDANCE TRACK™ TECHNOLOGY FOR USE WITH THE bq29330

bq20z70
SLUS686A – NOVEMBER 2005 – REVISED JUNE 2006
FEATURE SET
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Primary (1st Level) Safety Features
The bq20z70 supports a wide range of battery and system protection features that can easily be configured. The
primary safety features include:
• Cell over/under voltage protection
• Charge and Discharge over current
• Short Circut
• Charge and Discharge Over temperature
• AFE Watchdog
Secondary (2nd Level) Safety Features
The secondary safety features of the bq20z70 can be used to indicate more serious faults via the SAFE (pin 7).
This pin can be used to blow an in-line fuse to permanently disable the battery pack from charging or
discharging. The secondary safety protection features include:
• Safety over voltage
• Safety over current in Charge and Discharge
• Safety over temperature in Charge and Discharge
• Charge FET and 0 Volt Charge FET fault
• Discharge FET fault
• AFE communication fault
Charge Control Features
The bq20z70 charge control features include:
• Reports the appropriate charging current needed for constant current charging and the appropriate charging
voltage needed for constant voltage charging to a smart charger using SMBus broadcasts.
• Determines the chemical state of charge of each battery cell using Impedance Track™ and can reduce the
charge difference of the battery cells in fully charged state of the battery pack gradually using cell balancing
algorithm during charging. This prevents fully charged cells from overcharging and causing excessive
degradation and also increases the usable pack energy by preventing premature charge termination
• Supports pre-charging/zero-volt charging
• Support fast charging
• Supports charge inhibit and charge suspend if battery pack temperature is out of temperature range
• Reports charging fault and also indicate charge status via charge and discharge alarms.
Gas Gauging
The bq20z70 uses the Impedance Track™ Technology to measure and calculate the available charge in battery
cells. The achievable accuracy is better than 1% error over the lifetime of the battery and there is no full charge
discharge learning cycle required.
See Theory and Implementation of Impedance Track Battery Fuel-Gauging Algorithm application note
(SLUA364) for further details.
Authentication
The bq20z70 supports authentication by the host using SHA-1.
Power Modes
The bq20z70 supports 3 different power modes to reduce power consumption:
• In Normal Mode, the bq20z70 performs measurements, calculations, protection decisions and data updates
in 1 second intervals. Between these intervals, the bq20z70 is in a reduced power stage.
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