LTC2941
Battery Gas Gauge
with I
2
C Interface
FEATURES
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DESCRIPTION
The LTC
®
2941 measures battery charge state in battery-
supplied handheld PC and portable product applications.
Its operating range is perfectly suited for single cell Li-Ion
batteries. A precision coulomb counter integrates current
through a sense resistor between the battery’s positive
terminal and the load or charger. The measured charge
is stored in internal registers. An SMBus/I
2
C interface
accesses and configures the device.
The LTC2941 features programmable high and low thresh-
olds for accumulated charge. If a threshold is exceeded,
the device communicates an alert using either the SMBus
alert protocol or by setting a flag in the internal status
register.
The LTC2941 requires only a single low value external
sense resistor to set the current range.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Indicates Accumulated Battery Charge and
Discharge
High Accuracy Analog Integration
High Side Sense
1% Charge Accuracy
±50mV Sense Voltage Range
SMBus/I
2
C Interface
Configurable Alert Output/Charge Complete Input
2.7V to 5.5V Operating Range
Quiescent Current Less than 100μA
Small 6-Pin 2mm
×
3mm DFN package
APPLICATIONS
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Low Power Handheld Products
Cellular Phones
MP3 Player
Cameras
GPS
TYPICAL APPLICATION
Total Charge Error vs
Differential Sense Voltage
CHARGER
SENSE
+
I
2
C/SMBus
TO HOST
LTC2941
AL/CC
SDA
SENSE
–
SCL
GND
R
SENSE
100mΩ
LOAD
0.1μF
2.0
1.5
CHARGE ERROR (%)
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
0.1
1
V
SENSE
(mV)
2941 TA01b
V
SENSE+
= 3.6V
+
1-CELL
Li-Ion
2941 TA01a
10
100
2941f
1
LTC2941
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
PIN CONFIGURATION
TOP VIEW
SENSE
+
1
GND 2
SCL 3
7
GND
6 SENSE
–
5
AL/CC
4 SDA
Supply Voltage (SENSE
+
) ............................. –0.3V to 6V
SCL, SDA,
AL/CC
......................................... –0.3V to 6V
SENSE
–
.................................. –0.3V to (V
SENSE+
+ 0.3V)
Operating Ambient Temperature Range
LTC2941C ................................................ 0°C to 70°C
LTC2941I.............................................. –40°C to 85°C
Storage Temperature Range..................... –65°C to 150°
DCB PACKAGE
6-LEAD (2mm
×
3mm) PLASTIC DFN
T
JMAX
= 150°C,
θ
JA
= 120°C/W
EXPOSED PAD (PIN 7) IS GND, MUST BE SOLDERED TO PCB OR LEFT FLOATING
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
LTC2941CDCB#TRMPBF
TAPE AND REEL
LTC2941CDCB#TRPBF
PART MARKING*
LFKQ
PACKAGE DESCRIPTION
6-Lead (2mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
LTC2941IDCB#TRMPBF
LTC2941IDCB#TRPBF
LFKQ
6-Lead (2mm
×
3mm) Plastic DFN
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
SENSE+
I
SUPPLY
PARAMETER
Supply Voltage
Supply Current (Note 3)
Power Requirements
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 2)
CONDITIONS
MIN
2.7
Device On
Shutdown
Shutdown, V
SENSE+
≤ 4.2V
l
l
l
l
TYP
MAX
5.5
UNITS
V
μA
μA
μA
V
mV
kΩ
mAh
70
100
2.5
1
V
UVLO
V
SENSE
Undervoltage Lockout Threshold
Sense Voltage Differential Input Range
Differential Input Resistance, Across
SENSE
+
and SENSE
–
(Note 7)
V
SENSE+
Falling
V
SENSE+
– V
SENSE–
2.5
2.6
2.7
±50
Coulomb Counter
400
Prescaler M = 128 (Default),
R
SENSE
= 50mΩ
10mV ≤ |V
SENSE
| ≤ 50mV DC
10mV ≤ |V
SENSE
| ≤ 50mV, DC V
SENSE+
≤ 4.2V
1mV ≤ |V
SENSE
| ≤ 50mV DC (Note 7)
V
bat
Alert
V
bat
Alert Threshold
V
SENSE+
Falling, B[7:6] = 01
V
SENSE+
Falling, B[7:6] = 10
V
SENSE+
Falling, B[7:6] = 11
l
l
l
l
l
q
LSB
TCE
Charge LSB (Note 4)
Total Charge Error (Note 5)
0.085
±1
±1.5
±3.5
2.75
2.85
2.95
2.8
2.9
3
2.85
2.95
3.05
%
%
%
V
V
V
2941f
2
LTC2941
ELECTRICAL CHARACTERISTICS
SYMBOL
V
ITH
V
OL
I
IN
C
IN
t
PCC
PARAMETER
Logic Input Threshold,
AL/CC,
SCL,
SDA
Low Level Output Voltage,
AL/CC,
SDA I = 3mA
Input Leakage,
AL/CC,
SCL, SDA
Input Capacitance,
AL/CC,
SCL, SDA
Minimum Charge Complete (CC) Pulse
Width
Maximum SCL Clock Frequency
Bus Free Time Between Stop/Start
Minimum Repeated Start Setup Time
Minimum Hold Time (Repeated)
Start Condition
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 2)
CONDITIONS
l
l
l
l
MIN
0.3 •
V
SENSE+
TYP
MAX
0.7 •
V
SENSE+
0.4
1
10
1
UNITS
V
V
μA
pF
μs
Digital Inputs and Digital Outputs
V
IN
= V
SENSE+
/2
(Note 7)
I
2
C Timing Characteristics
f
SCL(MAX)
t
BUF(MIN)
t
SU,STA(MIN)
t
HD,STA(MIN)
400
900
1.3
600
600
600
100
0
kHz
μs
ns
ns
ns
ns
μs
t
SU,STO(MIN)
Minimum Setup Time for Stop
Condition
t
SU,DAT(MIN)
Minimum Data Setup Time Input
t
HD,DATI(MIN)
Minimum Data Hold Time Input
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
All currents into pins are positive, all voltages are referenced to
GND unless otherwise specified
Note 3:
I
SUPPLY
= I
SENSE+
+ I
SENSE–
Note 4:
The equivalent charge of an LSB in the accumulated charge
registers (C,D) depends on the value of R
SENSE
and the setting of the
internal pre-scaling factor M. It is calculated by:
50mΩ M
q
LSB
=
0.085mAh •
•
R
SENSE
128
See Choosing R
SENSE
and Coulomb Counter Prescaler M section for more
information.
1mAh = 3.6A • s = 3.6C (Coulomb), 0.085mAh = 306mC.
Note 5:
Deviation of q
LSB
from its nominal value.
Note 6:
C
B
= capacitance of one bus line in pF (10pF ≤ C
B
≤ 400pF).
Note 7:
Guaranteed by design, not subject to test.
TIMING DIAGRAM
t
of
SDA
t
SU, DAT
t
HD, DATO,
t
HD, DATI
t
SU, STA
t
HD, STA
t
BUF
t
SU, STO
2941 F01
SCL
t
HD, STA
START
CONDITION
REPEATED START
CONDITION
STOP
CONDITION
START
CONDITION
Figure 1. Definition of Timing on I
2
C Bus
2941f
3
LTC2941
TYPICAL PERFORMANCE CHARACTERISTICS
Total Charge Error vs Differential
Sense Voltage
3
2
CHARGE ERROR (%)
1
0
–1
–2
–3
0.1
V
SENSE+
= 2.7V
V
SENSE+
= 4.2V
1
V
SENSE
(mV)
2941 G01
Total Charge Error vs Supply
Voltage
1.00
0.75
CHARGE ERROR (%)
CHARGE ERROR (%)
0.50
0.25
0
1.00
0.75
0.50
0.25
0
–0.25
–0.50
V
SENSE
= –50mV
V
SENSE
= –10mV
2.5
3.0
3.5
4.0 4.5
5.0
V
SENSE+
(V)
5.5
6.0
–0.75
Total Charge Error vs Temperature
–0.25
–0.50
–0.75
–1.00
10
100
–1.00
–50
V
SENSE
= –50mV
V
SENSE
= –10mV
–25
25
0
50
TEMPERATURE (°C)
75
100
2941 G03
2941 G02
Supply Current vs Supply Voltage
100
90
80
70
60
50
40
2.5
0
T
A
= 25°C
T
A
= –40°C
T
A
= 85°C
1.5
I
SHUTDOWN
(μA)
I
SUPPLY
(μA)
2.0
Shutdown Supply Current vs
Supply Voltage
1.0
0.5
T
A
= 25°C
T
A
= –40°C
T
A
= 85°C
3.0
3.5
4.0 4.5
5.0
V
SENSE+
(V)
5.5
6.0
2.5
3.0
3.5
4.0 4.5
5.0
V
SENSE+
(V)
5.5
6.0
2941 G04
2941 G05
2941f
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LTC2941
PIN FUNCTIONS
SENSE
+
(Pin 1):
Positive Current Sense Input and Power
Supply. Connect to the load/charger side of the sense
resistor. V
SENSE+
operating range is 2.7V to 5.5V.
GND (Pin 2, Exposed Pad Pin 7):
Device Ground. Connect
directly to the negative battery terminal. Exposed pad may
be left open or connected to device ground.
SCL (Pin 3):
Serial Bus Clock Input.
SDA (Pin 4):
Serial Bus Data Input and Output.
AL/CC
(Pin 5):
Alert Output or Charge Complete Input.
Configured either as an SMBus alert output or charge
complete input by control register bits B[2:1]. At power-up,
the pin defaults to alert mode conforming to the SMBus
alert response protocol. It behaves as an open-drain logic
output that pulls to GND when a value in the threshold
registers is exceeded.
When configured as a charge complete input, connect
to the charge complete output from the battery charger
circuit. A high level at CC sets the value of the accumulated
charge (registers C, D) to FFFFh.
SENSE
–
(Pin 6):
Negative Current Sense Input. Connect
SENSE
–
to the positive battery terminal side of the sense
resistor. The voltage between SENSE
–
and SENSE
+
must
remain within ±50mV in normal operation.
2941f
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