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BATTERY PARAMETER MEASUREMENTS

Charge and Discharge Counting

Voltage

Current

Wake Function

Auto Calibration

Temperature

COMMUNICATIONS

SMBus On and Off State

bq20z90-V110

SLUS743 – NOVEMBER 2006

FEATURE SET (continued)

The bq20z90-V110 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 SRP and SRN pins. The integrating ADC measures

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

The bq20z90-V110 updates the individual series cell voltages through the bq29330 at one second intervals. The

bq20z90-V110 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 bq20z90. The internal ADC of the

bq20z90-V110 measures the voltage, scales it, and calibrates itself appropriately. This data is also used to

calculate the impedance of the cell for the Impedance Track™ gas-gauging.

The bq20z90-V110 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 bq20z90-V110 can exit sleep mode, if enabled, by the presence of a programmable level of current signal

across SRP and SRN.

The bq20z90-V110 provides an auto-calibration feature to cancel the voltage offset error across SRP and SRN

for maximum charge measurement accuracy. The bq20z90-V110 performs auto-calibration when the SMBus

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

The bq20z90-V110 TS1 and TS2 inputs, in conjunction with two identical NTC thermistors (default are Semitec

103AT), measure the battery environmental temperature. The bq20z90-V110 can also be configured to use its

internal temperature sensor.

The bq20z90-V110 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS

specification.

The bq20z90-V110 detects an SMBus off state when SMBC and SMBD are logic-low for

≥ 2 seconds. Clearing

this state requires either SMBC or SMBD to transition high. Within 1 ms, the communication bus is available.

Table 1. SBS COMMANDS

SBS Cmd

Mode

Name

Format

Size in

Min

Max

Default Value

Unit

Bytes

Value

Value

0x00

R/W

ManufacturerAccess

hex

2

0x0000

0xffff

—

0x01

R/W

RemainingCapacityAlarm

unsigned int

2

0

65535

300

mAh or

10mWh

0x02

R/W

RemainingTimeAlarm

unsigned int

2

0

65535

10

min

10

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