bq20z655-R1

SLUSAN9

– AUGUST 2011

www.ti.com

CONFIGURATION

Oscillator Function

The bq20z655-R1 fully integrates the system oscillators therefore, no external components are required for this

feature.

System Present Operation

The bq20z655-R1 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-R1 enters normal operating mode. When the pack is

removed from the system and the PRES input is high, the bq20z655-R1 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-R1 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

over time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.

Voltage

The bq20z655-R1 updates the individual series cell voltages at one second intervals. The internal ADC of the

bq20z655-R1 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-R1 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-R1 can exit sleep mode, if enabled, by the presence of a programmable level of current signal

across SRP and SRN.

Auto Calibration

The bq20z655-R1 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for

maximum charge measurement accuracy. The bq20z655-R1 performs auto-calibration when the SMBus lines

stay low continuously for a minimum of a programmable amount of time.

Temperature

The bq20z655-R1 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-R1 can be configured to use the internal temperature sensor or up to

2 external temperature sensors.

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© 2011, Texas Instruments Incorporated

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