1
Features
Provides accurate measurement
of available charge in NiCd,
NiMH, and Li-Ion batteries
Supports SBS v1.0 data set and
two-wire interface
Monitors charge FET in Li-Ion
pack protection circuit
Designed for battery pack inte-
gration
-
Low operating current
-
Complete circuit can fit on less
than square inch of PCB
space
Supports SBS charge control
commands for NiCd, NiMH, and
Li-Ion
Drives a four-segment LED dis-
play for remaining capacity
indication
16-pin narrow SOIC
General Description
The bq2040 Gas Gauge IC With
SMBus Interface is intended for
battery-pack or in-system installa-
tion to maintain an accurate record
of available battery charge. The
bq2040 directly supports capacity
monitoring for NiCd, NiMH, and Li-
Ion battery chemistries.
The bq2040 uses the System Man-
agement Bus v1.0 (SMBus) protocol
and supports the Smart Battery
Data (SBData) commands. The
bq2040 also supports the SBData
charge control functions.
Battery
state-of-charge, remaining capacity,
remaining time, and chemistry are
av a i l a b l e o v e r t h e s e r i a l l i n k .
Battery-charge state can be directly
indicated using a four-segment LED
display to graphically depict battery
full-to-empty in 25% increments.
The bq2040 estimates battery self-
discharge based on an internal
timer and temperature sensor and
user-programmable rate informa-
tion stored in external EEPROM.
The bq2040 also automatically re-
calibrates or "learns" battery capac-
ity in the full course of a discharge
cycle from full to empty.
The bq2040 may operate directly
from three nickel chemistry cells.
With the REF output and an exter-
nal transistor, a simple, inexpensive
regulator can be built to provide
V
CC
for other battery cell configu-
rations.
An external EEPROM is used to
program initial values into the
bq2040 and is necessary for proper
operation.
bq2040
Gas Gauge IC With SMBus Interface
V
CC
3.06.5V
ESCL
EEPROM clock
ESDA
EEPROM data
LED
1-4
LED segment 1-4
V
SS
System ground
SR
Sense resistor input
DISP
Display control input
1
PN204001.eps
16-Pin Narrow SOIC
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VCC
ESCL
ESDA
LED1
LED2
LED3
LED4
VSS
VOUT
REF
SMBC
SMBD
PSTAT
SB
DISP
SR
SB
Battery sense input
PSTAT
Protector status input
SMBD
SMBus data input/output
SMBC
SMBus clock
REF
Voltage reference output
V
OUT
EEPROM supply output
SLUS005JUNE 1999 E
Pin Connections
Pin Names
Pin Descriptions
V
CC
Supply voltage input
ESCL
Serial memory clock
Output used to clock the data transfer be-
tween the bq2040 and the external non-
volatile configuration memory.
ESDA
Serial memory data and address
Bidirectional pin used to transfer address
and data to and from the bq2040 and the ex-
ternal nonvolitile configuration memory.
LED
1
LED
4
LED display segment outputs
Each output may drive an external LED.
V
SS
Ground
SR
Sense resistor input
The voltage drop (V
SR
) across pins SR and
V
SS
is monitored and integrated over time
to interpret charge and discharge activity.
The SR input is connected to the sense re-
sistor and the negative terminal of the
battery. V
SR
< V
SS
indicates discharge, and
V
SR
> V
SS
indicates charge. The effective
voltage drop, V
SRO
, as seen by the bq2040
is V
SR
+ V
OS
. (See Table 3.)
DISP
Display control input
DISP high disables the LED display. DISP
floating allows the LED display to be active
during charge if the rate is greater than
100mA. DISP low activates the display for
4 seconds.
SB
Secondary battery input
Monitors the pack voltage through a high-
impedance resistor divider network.
The
pack voltage is reported in the SBD register
function Voltage (0x09) and is monitored for
end-of-discharge voltage and charging volt-
age parameters.
PSTAT
Protector status input
Provides overvoltage status from the Li-Ion
protector circuit and can initiate a charge sus-
pend request.
SMBD
SMBus data
Open-drain bidirectional pin used to transfer
address and data to and from the bq2040.
SMBC
SMBus clock
Open-drain bidirectional pin used to clock
the data transfer to and from the bq2040.
REF
Reference output for regulator
REF provides a reference output for an op-
tional FET-based micro-regulator.
V
OUT
Supply output
Supplies power to the external EEPROM con-
figuration memory.
2
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.
3
bq2040
VCC
VOUT
REF
SMBC
SMBD
PSTAT
SB
SR
DISP
ESCL
ESDA
LED1
LED2
LED3
LED4
bq2040
VSS
2040LED.eps
301K
BSS138
100K
100K
100K
100K
100K
100K
100K
86.5K
604K
806K
604K
499K
806K
499K
604K
909K
BSS138
BSS138
2N7002
BSS138
2N7002
2N7002
2N7002
2
R5
R4
Q1
R11
No. of Cells
Chart 1
For bq2040 With No D8
Li-Ion
NiMH
3
4
6
8
9
10
12
499K
499K
698K
698K
806K
909K
909K
(Optional)
(Optional)
Figure 1. Battery Pack Application Diagram--LED Display
4
bq2040
Parameter Name
Address
Description
Length
Units
EEPROM length
0x00
Number of EEPROM data locations
must = 0x64
8 bits
NA
EEPROM check1
0x01
EEPROM data integrity check byte, must = 0x5b
8 bits
NA
Remaining time alarm
0x02/0x03 Sets RemainingTimeAlarm (0x02)
16 bits
minutes
Remaining capacity alarm
0x04/0x05 Sets RemainingCapacityAlarm (0x01)
16 bits
mAh
Reserved
0x06/0x07 Reserved for future use
16 bits
NA
Initial charging current
0x08/0x09 Sets the initial charging current
16 bits
mA
Charging voltage
0x0a/0x0b Sets ChargingVoltage (0x15)
16 bits
mV
Battery status
0x0c/0x0d Initializes BatteryStatus (0x16)
16 bits
NA
Cycle count
0x0e/0x0f Initializes and stores CycleCount (0x17)
16 bits
cycles
Design capacity
0x10/0x11 Sets DesignCapacity (0x18)
16 bits
mAh
Design voltage
0x12/0x13 Sets DesignVoltage (0x19)
16 bits
mV
Specification information
0x14/0x15 Programs SpecificationInfo (0x1a)
16 bits
NA
Manufacture date
0x16/0x17 Programs ManufactureDate (0x1b)
16 bits
NA
Serial number
0x18/0x19 Programs SerialNumber (0x1c)
16 bits
NA
Fast-charging current
0x1a/0x1b Sets ChargingCurrent (0x14)
16 bits
mA
Maintenance-charge current
0x1c/0x1d Sets the trickle current request
16 bits
mA
Reserved
0x1e/0x1f Reserved must = 0x0000
16 bits
mAh
Manufacturer name
0x20-0x2b Programs ManufacturerName (0x20)
96 bits
NA
Current overload
0x2c/0x2d Sets the overload current threshold
16 bits
mA
Battery low %
0x2e
Sets the battery low amount
8 bits
%
Reserved
0x2f
Reserved for future use
8 bits
NA
Device name
0x30-0x37 Programs DeviceName (0x21)
64 bits
NA
Li-Ion taper current
0x38/0x39
Sets the upper limit of the taper current for charge
termination
16 bits
mA
Maximum overcharge limit
0x3a/0x3b Sets the maximum amount of overcharge
16 bits
NA
Reserved
0x3c
Reserved must = 0x00
8 bits
NA
Access protect
0x3d
Locks commands outside of the SBS data set
8 bits
NA
FLAGS1
0x3e
Initializes FLAGS1
8 bits
NA
FLAGS2
0x3f
Initializes FLAGS2
8 bits
NA
Device chemistry
0x40-0x45 Programs DeviceChemistry (0x22)
48 bits
NA
Current measurement gain
0x46/0x47 Sense resistor calibration value
16 bits
NA
Battery voltage offset
0x48
Voltage calibration value
8 bits
NA
Temperature offset
0x49
Temperature calibration value
8 bits
NA
Maximum temperature and
T step
0x4a
Sets the maximum charge temperature and the
T
step for
T/
t termination
8 bits
NA
Table 1. Configuration Memory Map
5
bq2040
Parameter Name
Address
Description
Length
Units
Charge efficiency
0x4b
Sets the high/low charge rate efficiencies
8 bits
NA
Full charge percentage
0x4c
Sets the percent at which the battery is consid-
ered fully charged
8 bits
NA
Digitial filter
0x4d
Sets the minimum charge/discharge threshold
8 bits
NA
Current integration gain
0x4e
Programs the current integration gain to the
sense resistor value
8 bits
NA
Self-discharge rate
0x4f
Sets the battery's self-discharge rate
8 bits
NA
Manufacturer data
0x50-0x55 Programs ManufacturerData (0x23)
48 bits
NA
Voltage gain1
0x56/0x57 Battery divider calibration value
16 bits
NA
Reserved
0x58-0x59 Reserved
16 bits
NA
EDVF charging current
0x5a/0x5b
Sets the charge current request when the battery
voltage is less than EDVF
16 bits
NA
End of discharge voltage1
0x5c/0x5d Sets EDV1
16 bits
NA
End of discharge voltage final
0x5e/0x5f Sets EDVF
16 bits
NA
Full-charge capacity
0x60/0x61 Initializes and stores FullChargeCapacity (0x10)
16 bits
mAh
t step
0x62
Sets the
t step for
T/
t termination
8 bits
NA
Hold-off time
0x63
Sets
T/
t hold-off timer
8 bits
NA
EEPROM check 2
0x64
EEPROM data integrity check byte
must = 0xb5
8 bits
NA
Reserved
0x65-0x7f Reserved for future use
NA
Table 1. Configuration Memory Map (Continued)
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