BQ2040 Datasheet, PDF (3/33 Pages) Texas Instruments – Gas Gauge IC With SMBus Interface

bq2040
Functional Description
General Operation
The bq2040 determines battery capacity by monitoring
the amount of charge put into or removed from a re-
chargeable battery. The bq2040 measures discharge
and charge currents, estimates self-discharge, and
monitors the battery for low-battery voltage thresholds.
The charge is measured by monitoring the voltage
across a small-value series sense resistor between the
battery's negative 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
bq2040 using the LED capacity display, the serial port,
and an external EEPROM for battery pack program-
ming information. The bq2040 must be configured and
calibrated for the battery-specific information to ensure
proper operation. Table 1 outlines the configuration in-
formation that must be programmed in the EEPROM.
An internal temperature sensor eliminates the need
for an external thermistor—reducing cost and compo-
nents. An internal, temperature-compensated time-
base eliminates the need for an external resonator,
further reducing cost and components. The entire cir-
cuit
in
Figure
1
can
occupy
less
than
3
4
square
inch
of
board space.
VCC
ESCL
ESDA
LED1
LED2
LED3
LED4
VSS
VOUT
REF
SMBC
SMBD
PSTAT
SB
DISP
SR
bq2040
(Optional)
Chart 1
For bq2040 With No D8
No. of Cells
R5
R11 R4
2
301K 604K 100K
3
499K 806K 100K
4
698K 604K 100K
6
499K 499K 100K
8
698K 806K 100K
9
806K 499K 100K
10
909K 604K 100K
12
909K 909K 86.5K
Q1
BSS138
BSS138
2N7002
BSS138
BSS138
2N7002
2N7002
2N7002
(Optional)
Figure 1. Battery Pack Application Diagram—LED Display
2040LED.eps
3