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Power Modes

CONFIGURATION

Oscillator Function

System Present Operation

BATTERY PARAMETER MEASUREMENTS

Charge and Discharge Counting

Voltage

Current

Auto Calibration

Temperature

bq20z70

SLUS686B – NOVEMBER 2005 – REVISED JULY 2007

FEATURE SET (continued)

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.

• In Sleep Mode, the bq20z70 performs measurements, calculations, protection decisions and data update in

adjustable time intervals. Between these intervals, the bq20z70 is in a reduced power stage. The bq20z70

has a wake function that enables exit from Sleep mode, when current flow or failure is detected.

• In Shutdown Mode the bq20z70 is completely disabled.

The bq20z70 fully integrates the system oscillators. Therefore, the bq20z70 requires no external components for

this feature.

The bq20z70 pulls the PU pin high periodically (1 s). Connect this pin to the PRES pin of the bq20z70 via a

resistor of approximately 5 k

Ω. The bq20z70 measures the PRES input during the PU-active period to determine

its state. If PRES input is pulled to ground by external system, the bq20z70 detects this as system present.

The bq20z70 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.

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

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

The bq20z70 updates the individual series cell voltages through the bq29330 at one second intervals. The

bq20z70 configures the bq29330 to connect the selected cell, cell offset, or bq29330 VREF to the CELL pin of

the bq29330, which is required to be connected to VIN of the bq20z70. The internal ADC of the bq20z70

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.

The bq20z70 uses the SRP and SRN inputs to measure and calculate the battery charge and discharge current

using a 5 m

Ω to 20 mΩ typ. sense resistor.

The bq20z70 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for

maximum charge measurement accuracy. The bq20z70 performs auto-calibration when the SMBus lines stay

low continuously for a minimum of 5 s.

The bq20z70 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 enviromental

temperature. The bq20z70 can be configured to use internal or external temperature sensors.

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