bq20z45
www.ti.com .................................................................................................................................................................................................. SLUS800–MARCH 2009
FEATURE SET
Primary (1st Level) Safety Features
The bq20z45 supports a wide range of battery and system protection features that can easily be configured. The
primary safety features include:
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Cell over/undervoltage protection
Charge and discharge overcurrent
Short Circuit
Charge and discharge overtemperature with independent alarms and thresholds for each thermistor
AFE Watchdog
Secondary (2nd Level) Safety Features
The secondary safety features of the bq20z45 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:
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Safety overvoltage
Safety undervoltage
Safety overcurrent in charge and discharge
Safety overtemperature in charge and discharge with independent alarms and thresholds for each thermistor
Charge FET and 0 Volt Charge FET fault
Discharge FET fault
Cell imbalance detection (active and at rest)
Open thermistor detection
AFE communication fault
Charge Control Features
The bq20z45 charge control features include:
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Supports JEITA temperature ranges. Reports charging voltage and charging current according to the active
temperature range.
Handles more complex charging profiles. Allows for splitting the standard temperature range into 2
sub-ranges and allows for varying the charging current according to the cell voltage.
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
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Supports pre-charging/zero-volt 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 bq20z45 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.
Copyright © 2009, Texas Instruments Incorporated
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