FEATURE SET

Primary (1st Level) Safety Features

Secondary (2nd Level) Safety Features

Charge Control Features

Gas Gauging

bq20z45

The bq20z45 supports a wide range of battery and system protection features that can easily be configured. The

primary safety features include:

• Cell over/undervoltage protection

• Charge and discharge overcurrent

• Short Circuit

• Charge and discharge overtemperature with independent alarms and thresholds for each thermistor

• AFE Watchdog

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:

• 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

The bq20z45 charge control features include:

• 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

• 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.

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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Product Folder Link(s): bq20z45