BQ2012SN datasheet(3/20 Pages) TI

3 / 20 page

Functional Description

General Operation

The bq2012 determines battery capacity by monitoring

the amount of charge input to or removed from a re-

chargeable battery. The bq2012 measures discharge and

charge currents, estimates self-discharge, monitors the

battery for low-battery voltage thresholds, and compen-

sates for temperature and charge/discharge rates. The

charge measurement is made by monitoring the voltage

across a small-value series sense resistor between the

negative battery terminal and ground.

The available

battery charge is determined by monitoring this voltage

over time and correcting the measurement for the envi-

ronmental and operating conditions.

Figure 1 shows a typical battery pack application of the

bq2012 using the LED display capability as a charge-

state indicator. The bq2012 can be configured to display

capacity in either a relative or an absolute display mode.

The relative display mode uses the last measured dis-

charge capacity of the battery as the battery “full” refer-

ence. The absolute display mode uses the programmed

full count (PFC) as the full reference, forcing each seg-

ment of the display to represent a fixed amount of

charge. A push-button display feature is available for

momentarily enabling the LED display.

The bq2012 monitors the charge and discharge currents

as a voltage across a sense resistor (see RS in Figure 1).

A filter between the negative battery terminal and the

SR pin may be required if the rate of change of the bat-

tery current is too great.

bq2012

FG201201.eps

SEG6/PROG6

SEG5/PROG5

SEG4/PROG4

SEG3/PROG3

SEG2/PROG2

SEG1/PROG1

DISP

VCC

REF

bq2012

Gas Gauge IC

LCOM

VSS

EMPTY

VCC

0.1 F

ZVNL110A

RB1

RB2

Load

Charger

Indicates optional.

Directly connect to VCC across 3 or 4 cells (3 to 4.8V nominal,should not

exceed 6.5V) with a resistor and a Zener diode to limit voltage during charge.

Otherwise, R1, C1, and Q1 are needed for regulation of >4 cells.

The value of R1 depends on the number of cells.

Programming resistors (6 max.) and ESD-protection diodes are not shown.

R-C on SR may be required (application-specific), where the R

should not exceed 100k.

VCC

CHG

Figure 1. Battery Pack Application Diagram—LED Display

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