bq20z95

SLUS757C – JULY 2007 – REVISED OCTOBER 2013

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Power Modes

The bq20z95 supports three power modes to reduce power consumption:

•

In NORMAL mode, the bq20z95 performs measurements, calculations, protection decisions and data updates

in 1-s intervals. Between these intervals, the bq20z95 is in a reduced power stage.

•

In SLEEP mode, the bq20z95 performs measurements, calculations, protection decisions, and data updates

in adjustable time intervals. Between these intervals, the bq20z95 is in a reduced power stage. The bq20z95

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

•

In SHUTDOWN mode the bq20z95 is completely disabled.

CONFIGURATION

Oscillator Function

The bq20z95 fully integrates the system oscillators. Therefore, the bq20z95 requires no external components for

this feature.

System Present Operation

The bq20z95 checks the PRES pin periodically (1s). If PRES input is pulled to ground by external system, the

bq20z95 detects this as system present.

BATTERY PARAMETER MEASUREMENTS

The bq20z95 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

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

Voltage

The bq20z95 updates the individual series cell voltages at 1-s intervals. The internal ADC of the bq20z95

measures the voltage, and 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 bq20z95 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.

Auto Calibration

The bq20z95 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for

maximum charge measurement accuracy. The bq20z95 performs auto-calibration when the SMBus lines stay

low continuously for a minimum of 5 s.

Temperature

The bq20z95 has an internal temperature sensor and two 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 bq20z95 can be configured to use internal or up to two external temperature sensors.

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