LTC2943
1
2943fa
For more information www.linear.com/LTC2943
TYPICAL APPLICATION
FEATURES DESCRIPTION
Multicell Battery Gas Gauge
with Temperature, Voltage
and Current Measurement
The LT C
®
2943 measures battery charge state, battery volt-
age, battery current and its own temperature in portable
product applications. The wide input voltage range allows
use with multicell batteries up to 20V. A precision coulomb
counter integrates current through a sense resistor between
the battery’s positive terminal and the load or charger.
Voltage, current and temperature are measured with an
internal 14-bit No Latency ΔΣ™ ADC. The measurements
are stored in internal registers accessible via the onboard
I2C/SMBus Interface.
The LTC2943 features programmable high and low thresh-
olds for all four measured quantities. If a programmed
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 LTC2943 requires only
a single low value sense resistor to set the measured
current range.
Total Charge Error vs
Differential Sense Voltage
APPLICATIONS
n Measures Accumulated Battery Charge and Discharge
n 3.6V to 20V Operating Range for Multiple Cells
Application
n 14-Bit ADC Measures Voltage, Current and
Temperature
n 1% Voltage, Current and Charge Accuracy
n ±50mV Sense Voltage Range
n High Side Sense
n General Purpose Measurements for Any Battery
Chemistry and Capacity
n I2C/SMBus Interface
n Configurable Alert Output/Charge Complete Input
n Quiescent Current Less Than 120µA
n Small 8-Lead 3mm × 3mm DFN Package
n Power Tools
n Electric Bicycles
n Portable Medical Equipment
n Video Cameras
L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks and
No Latency ΔΣ and PowerPath are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
VSENSE (mV)
0.1
–2.0
CHARGE ERROR (%)
0
–0.5
–1.0
–1.5
1.5
1.0
0.5
2.0
1 10 100
2943 TA01b
VSENSE+ = 10V
SENSE+
ALCC
SDA
SCL
LTC2943
CHARGER
2k2k 2k
1A
LOAD
RSENSE
50mΩ
MULTICELL
LI-ION
2943 TA01a
SENSE–
+
GND
1µF
VDD
3.3V
µP
LTC2943
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PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
TOP VIEW
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
5
6
7
8
9
4
3
2
1SENSE+
GND
GND
SCL
SENSE–
GND
ALCC
SDA
TJMAX = 150°C, θJA = 100°C/W
EXPOSED PAD (PIN 9) PCB GND CONNECTION OPTIONAL
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Power Requirements
VSENSE+Supply Voltage 3.6 20 V
ISUPPLY Supply Current (Note 3) Battery Gas Gauge On, ADC Sleep
Battery Gas Gauge On, ADC On
Shutdown
l
l
l
80
650
15
120
750
25
µA
µA
µA
ISENSE+Pin Current (Note 3) Battery Gas Gauge On, ADC Sleep
Battery Gas Gauge On, ADC On
Shutdown
80
500
15
µA
µA
µA
ISENSE–Pin Current (Note 3) Battery Gas Gauge On, ADC Sleep
Battery Gas Gauge On, ADC On
Shutdown
1
150
1
µA
µA
µA
VUVLO Undervoltage Lockout Threshold VSENSE+ Falling l3.0 3.3 3.6 V
Coulomb Counter
VSENSE Sense Voltage Differential Input
Range
VSENSE+ – VSENSE–l±50 mV
RIDR Differential Input Resistance Across
SENSE+ and SENSE– (Note 8)
400 kΩ
qLSB Charge LSB (Note 4) Prescaler M = 4096(Default), RSENSE = 50mΩ 0.340 mAh
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2)
ORDER INFORMATION
Supply Voltage (SENSE+) ........................... –0.3V to 24V
SCL, SDA, ALCC Voltage .............................. –0.3V to 6V
SENSE– ...............(–0.3V + VSENSE+) to (VSENSE+ + 0.3V)
Operating Ambient Temperature Range
LTC2943C ............................................... 0°C to 70°C
LTC2943I ............................................–40°C to 85°C
Storage Temperature Range .................. –65°C to 150°C
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2943CDD#PBF LTC2943CDD#TRPBF LGCS 8-Lead (3mm × 3mm) Plastic DFN 0°C to 70°C
LTC2943IDD#PBF LTC2943IDD#TRPBF LGCS 8-Lead (3mm × 3mm) Plastic DFN –40°C to 85°C
Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
LTC2943
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ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
TCE Total Charge Error (Note 5) 10mV ≤ |VSENSE| ≤ 50mV DC
10mV ≤ |VSENSE| ≤ 50mV DC
1mV ≤ |VSENSE| ≤ 10mV DC (Note 8)
l
l
±1
±1.5
±3.5
%
%
%
VOSE Effective Differential Offset Voltage
(Note 9)
VSENSE ≥ 500µV, VSENSE+ = 10V l5 10 µV
Voltage Measurement ADC
Resolution (No Missing Codes) (Note 8) l14 Bits
VFS(V) Full-Scale Voltage Conversion 23.6 V
ΔVLSB Quantization Step of 14-Bit Voltage
ADC
(Note 6) 1.44 mV
TUEVVoltage Total Unadjusted Error
l
1
1.3
%
%
GainVVoltage Gain Accuracy l1.3 %
INLVIntegral Nonlinearity VSENSE+ > 5V l±1 ±4 LSB
3.6V ≤ VSENSE+ ≤ 5V l±8 LSB
TCONV(V) Voltage Conversion Time l48 ms
Current Measurement ADC
Resolution (No Missing Codes) (Note 8) l12 Bits
VFS(I) Full-Scale Current Conversion l±60 mV
VSENSE Sense Voltage Differential Input
Range
VSENSE+ – VSENSE–l±50 mV
ΔILSB Quantization Step of 12-Bit Current
ADC
(Note 6) 29.3 µV
GainICurrent Gain Accuracy
l
1
1.3
%
%
VOS(I) Offset ±1 ±10 LSB
INLIIntegral Nonlinearity l±1 ±4 LSB
TCONV(I) Current Conversion Time l8 ms
Temperature Measurement ADC
Resolution (No Missing Codes) (Note 8) l11 Bits
TFS Full-Scale Temperature 510 K
ΔTLSB Quantization Step of 11-Bit
Temperature ADC
(Note 6) 0.25 K
TUETTemperature Total Unadjusted Error VSENSE+ ≥ 5V
(Note 8)
l
±3
±5
K
K
TCONV(T) Temperature Conversion Time l8 ms
Digital Inputs and Digital Outputs
VITH(HV) Logic Input Threshold VSENSE+ ≥ 5V l0.8 2.2 V
VITH(LV)3.6V < VSENSE+ < 5V 0.5 1.8 V
VOL Low Level Output Voltage, ALCC,
SDA
I = 3mA, VSENSE+ ≥ 5V l0.4 V
IIN Input Leakage, ALCC, SCL, SDA VIN = 5V l1 µA
CIN Input Capacitance, ALCC, SCL, SDA (Note 8) l10 pF
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TIMING DIAGRAM
ELECTRICAL CHARACTERISTICS
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. ISUPPLY = ISENSE+ + ISENSE–. In most operating modes, ISUPPLY is
flowing in SENSE+ pin. Only during ADC conversions, current is flowing in
SENSE– pin as well. Typically, ISENSE– = VSENSE–/150k during ADC voltage
conversion and ISENSE– = 20µA during ADC current conversion.
Note 4. The equivalent charge of an LSB in the accumulated charge
register depends on the value of RSENSE and the setting of the internal
prescaling factor M:
qLSB = 0.340mAh • (50mΩ/RSENSE) • (M/4096)
See Choosing RSENSE and Choosing Coulomb Counter Prescaler M section
for more information. 1mAh = 3.6C (Coulombs)
Note 5. Deviation of qLSB from its nominal value.
Note 6. The quantization step of the 14-bit ADC in voltage mode,12-bit
ADC in current mode and 11-bit ADC in temperature mode is not the
same as the LSB of the respective combined 16-bit registers. See Voltage,
Current and Temperature Registers section for more information.
Note 7. CB = Capacitance of one bus line in pF (10pF ≤ CB ≤ 400pF).
Note 8. Guaranteed by design, not subject to test.
Note 9. See Effect of Differential Offset Voltage on Total Charge Error
section.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
tPCC Minimum Charge Complete (CC)
Pulse Width
1 µs
I2C Timing Characteristics
fSCL(MAX) Maximum SCL Clock Frequency l400 900 kHz
tBUF(MAX) Bus Free Time Between Stop/Start l1.3 µs
tSU(STA(MIN)) Minimum Repeated Start Set-Up
Time
l600 ns
tHD(STA(MIN)) Minimum Hold Time (Repeated)
Start Condition
l600 ns
tSU(STO(MIN)) Minimum Set-Up Time for Stop
Condition
l600 ns
tSU(DAT(MIN)) Minimum Data Setup Time Input l100 ns
THD(DAT(MIN)) Minimum Data Hold Time Input l50 ns
THDDATO Data Hold Time Input Output l0.3 0.9 µs
TOF Data Output Fall Time (Notes 7, 8) l20 + 0.1 • CB300 ns
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
Figure 1. Definition of Timing on I2C Bus
SDA
SCL
2943 TD01
tHD(STA)
START
CONDITION
tSU(DAT) tHD(DAT0)
tHD(DAT1) tHD(STA) tSU(STO)
tSU(STA)
STOP
CONDITION
START
CONDITION
REPEATED START
CONDITION
tOF
tBUF
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TYPICAL PERFORMANCE CHARACTERISTICS
Current Measurement ADC
Integral Nonlinearity
Current Measurement ADC
Gain Error
Supply Current vs Supply Voltage
Shutdown Supply Current vs
Supply Voltage
Voltage Measurement ADC
Total Unadjusted Error
Total Charge Error vs Differential
Sense Voltage
Total Charge Error vs Supply
Voltage
Total Charge Error vs
Temperature
Voltage Measurement ADC
Integral Nonlinearity
VSENSE+ (V)
0
CHARGE ERROR (%)
–1.00
–0.50
–0.25
0
1.00
0.25
10 15 20
2943 G02
–0.75
0.50
0.75
525
VSENSE = 10mV
VSENSE = 50mV
TEMPERATURE (°C)
–50
CHARGE ERROR (%)
–1.00
–0.50
–0.25
0
0.50
25 50
2943 G03
–0.75
0.75
1.00
0.25
–25 0 75 100
VSENSE = 10mV
VSENSE = 50mV
VSENSE+ (V)
0
ISUPPLY (µA)
80
90
110
100
2943 G04
70
60
5 10 15 20 25
50
40
TA = 25°C
TA = –40°C
TA = 85°C
VSENSE+ (V)
0
5
ISUPPLY (µA)
10
15
25
30
5 2015
2943 G05
20
10 25
TA = 85°C
TA = –40°C
TA = 25°C
VSENSE– (V)
0
INL (VLSB)
15
2944 G07
–2
0
2
4
–8
–4
–6
5 10 20 25
TA = –40°C
TA = 85°C
TA = 25°C
VSENSE– (V)
0
–1.0
TOTAL UNADJUSTED ERROR (%)
0
1.0
0.5
15 20
2943 G06
–0.5
510 25
TA = 85°C
TA = 25°C
TA = –40°C
VSENSE (mV)
0.1
–1
CHARGE ERROR (%)
0
–2
2
1
1 10 100
2943 G01
–3
3VSENSE+ = 3.6V TO 20V
VSENSE (mV)
INL (ILSB)
0
2943 G09
–1
0
1
2
–3
–50 –25 25 50
3
–2
VCC = 10V, TA = –40° TO 85°C
VSENSE– (V)
–1.0
GAIN ERROR (%)
–0.5
0
1.0
15
2943 G08
0.5
50 10 20 25
TA = –40°C TO 85°C
LTC2943
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PIN FUNCTIONS
SENSE+ (Pin 1): Positive Current Sense Input and Power
Supply. Connect to load/charger side of the sense resistor.
VSENSE+ operating range is 3.6V to 20V. SENSE+ is also
an input to the ADC during current measurement. Bypass
to GND with a 1µF capacitor located as close to pin 1 and
pin 2 as possible.
GND (Pin 2, Pin 3, Pin 7): Device Ground. Connect directly
to the negative battery terminal.
SCL (Pin 4): Serial Bus Clock Input.
SDA (Pin 5): Serial Bus Data Input and Output.
ALCC (Pin 6): 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 any threshold register value
is exceeded. When configured as a charge complete input,
connect to the charge complete output from the battery
charger circuit. A low level at CC sets the value of the
accumulated charge (registers C, D) to FFFFh.
SENSE– (Pin 8): 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. SENSE– is also
an input to the ADC during voltage and current measure-
ment.
Exposed Pad (Pin 9): Exposed pad may be left open or
connected to device ground (GND).
TYPICAL PERFORMANCE CHARACTERISTICS
Current Measurements Noise
Voltage Measurements Noise
Temperature Error vs Temperature
29.3µV/LSB
–3
0
COUNTS
250
200
150
100
50
300
350
400
450
–2 –1 210 3
2943 G12
800 READINGS
TEMPERATURE (°C)
–50 –25
–3
TEMPERATURE ERROR (°C)
–2
–1
0
1
2
3
0 755025 100
2943 G10
VSENSE+ = 3.6V
VSENSE+ = 5.5V
VSENSE+ = 10V
VSENSE+ = 20V
1.44mV/LSB
0
COUNTS
500
400
300
200
100
600
700
800
900
–2 –1 210
2943 G11
LTC2943
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OPERATION
Overview
The LTC2943 is a battery gas gauge designed for use
with multicell batteries with terminal voltages from 3.6V
to 20V. It measures battery charge and discharge, battery
voltage, current and its own temperature.
A precision analog coulomb counter integrates current
through a sense resistor between the battery’s positive
terminal and the load or charger. Battery voltage, battery
current and silicon temperature are measured with an
internal ADC.
Coulomb Counter
Charge is the time integral of current. The LTC2943 mea-
sures charge by monitoring the voltage developed across
a sense resistor. The differential voltage between SENSE+
and SENSE– is applied to an auto-zeroed differential analog
integrator to infer charge.
When the integrator output ramps to REFHI or REFLO
levels, switches S1, S2, S3 and S4 toggle to reverse the
ramp direction (Figure 2). By observing the condition of
the switches and the ramp direction, polarity is determined.
This approach also significantly lowers the impact on offset
of the analog integrator as described in the Differential
Offset Voltage section.
A programmable prescaler effectively increases integration
time by a factor M programmable from 1 to 4096. At each
underflow or overflow of the prescaler, the accumulated
charge register (ACR) value is incremented or decremented
one count. The value of accumulated charge is read via
the I2C interface.
Voltage, Current and Temperature ADC
The LTC2943 includes a 14-bit No Latency ΔΣ analog-to-
digital converter, with internal clock and voltage reference
circuits.
The ADC can be used to monitor the battery voltage at
SENSE– or the battery current flowing through the sense
resistor or to convert the output of the on-chip tempera-
ture sensor.
Conversion of voltage, current and temperature are trig-
gered by programming the control register via the I2C
interface. The LTC2943 includes a scan mode where
voltage, current and temperature conversion measure-
ments are executed every 10 seconds. At the end of each
conversion the corresponding registers are updated and
the converter goes to sleep to minimize quiescent current.
The temperature sensor generates a voltage proportional
to temperature with a slope of 2mV/K resulting in a volt-
age of 600mV at 27°C.
Power-Up Sequence
When SENSE+ rises above a threshold of approximately
3.3V, the LTC2943 generates an internal power-on reset
(POR) signal and sets all registers to their default state.
In the default state, the coulomb counter is active while
the voltage, current and temperature ADC is switched
off. The accumulated charge register is set to mid-scale
(7FFFh), all low threshold registers are set to 0000h and all
high threshold registers are set to FFFFh. The alert mode
is enabled and the coulomb counter prescaling factor M
is set to 4096.
2943 F02
REFHI
S1
VCC
S2
S3
S4
REFLO
GND
SENSE+
RSENSE
IBAT
BATTERY
+
LOADCHARGER
SENSE–
1
8
2
M
PRESCALER
ACR
–
+
–
+
–
+
CONTROL
LOGIC
POLARITY
DETECTION
Figure 2. Coulomb Counter Section of the LTC2943
LTC2943
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Internal Registers
The LTC2943 register map is shown in Table 1. The
LTC2943 integrates current through a sense resistor,
measures battery voltage, current and temperature and
stores the results in internal 16-bit registers accessible
via I2C. High and low limits can be programmed for each
measured quantity. The LTC2943 continuously monitors
these limits and sets a flag in the status register when a
limit is exceeded. If the alert mode is enabled, the ALCC
pin pulls low.
Table 1. Register Map
ADDRESS NAME REGISTER DESCRIPTION R/W DEFAULT
00h A Status R See Table 2
01h B Control R/W 3Ch
02h C Accumulated Charge MSB R/W 7Fh
03h D Accumulated Charge LSB R/W FFh
04h E Charge Threshold High MSB R/W FFh
05h F Charge Threshold High LSB R/W FFh
06h G Charge Threshold Low MSB R/W 00h
07h H Charge Threshold Low LSB R/W 00h
08h I Voltage MSB R 00h
09h J Voltage LSB R 00h
0Ah K Voltage Threshold High MSB R/W FFh
0Bh L Voltage Threshold High LSB R/W FFh
0Ch M Voltage Threshold Low MSB R/W 00h
0Dh N Voltage Threshold Low LSB R/W 00h
0Eh O Current MSB R 00h
0Fh P Current LSB R 00h
10h Q Current Threshold High MSB R/W FFh
11h R Current Threshold High LSB R/W FFh
12h S Current Threshold Low MSB R/W 00h
13h T Current Threshold Low LSB R/W 00h
14h U Temperature MSB R 00h
15h V Temperature LSB R 00h
16h W Temperature Threshold High R/W FFh
17h X Temperature Threshold Low R/W 00h
R = Read, W = Write
APPLICATIONS INFORMATION
The status of the charge, voltage, current and temperature
alerts is reported in the status register shown in Table 2.
Table 2. Status Register (A)
BIT NAME OPERATION DEFAULT
A[7] Reserved
A[6] Current Alert Indicates one of the current
limits was exceeded 0
A[5]
Accumulated
Charge
Overflow/
Underflow
Indicates that the value of the
ACR hit either top or bottom 0
A[4] Temperature
Alert
Indicates one of the
temperature limits was
exceeded
0
A[3] Charge Alert
High
Indicates that the ACR value
exceeded the charge threshold
high limit
0
A[2] Charge Alert
Low
Indicates that the ACR value
exceeded the charge threshold
low limit
0
A[1] Voltage Alert Indicates one of the voltage
limits was exceeded 0
A[0] Undervoltage
Lockout Alert
Indicates recovery from
undervoltage. If set to 1, a
UVLO has occurred and the
contents of the registers are
uncertain
1
After each voltage, current or temperature conversion, the
conversion result is compared to the respective threshold
registers. If a value in the threshold registers is exceeded,
the corresponding bit A[6], A[4] or A[1] is set.
The accumulated charge register (ACR) is compared to
the charge thresholds every time the analog integrator
increments or decrements the prescaler. If the ACR value
exceeds the threshold register values, the corresponding
bit A[3] or A[2] are set. Bit A[5] is set if the accumulated
charge registers (ACR) overflows or underflows. At each
overflow or underflow, the ACR rolls over and resumes
integration.
The undervoltage lockout (UVLO) bit of the status register
A[0] is set if, during operation, the voltage on the SENSE+
pin drops below 3.5V without reaching the POR level. The
analog parts of the coulomb counter are switched off while
the digital register values are retained. After recovery of the
supply voltage the coulomb counter resumes integrating
with the stored value in the accumulated charge registers
but it has missed any charge flowing while SENSE+ < 3.5V.
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All status register bits are cleared after being read by the
host, but might be reasserted after the next temperature,
voltage or current conversion or charge integration, if the
corresponding alert condition is still fulfilled.
Control Register (B)
The operation of the LTC2943 is controlled by program-
ming the control register. Table 3 shows the organization
of the 8-bit control register B[7:0].
Table 3. Control Register B
BIT NAME OPERATION DEFAULT
B[7:6] ADC Mode [11] Automatic Mode:
continuously performing
voltage, current and temperature
conversions
[10] Scan Mode: performing
voltage, current and temperature
conversion every 10s
[01] Manual Mode: performing
single conversions of voltage,
current and temperature then
sleep
[00] Sleep
[00]
B[5:3] Prescaler M Sets coulomb counter prescaling
factor M between 1 and 4096.
Default is 4096.
Maximum value is limited to 4096
[111]
B[5:3] M
000 1
001 4
010 16
011 64
100 256
101 1024
110 4096
111 4096
BIT NAME OPERATION DEFAULT
B[2:1] ALCC
Configure
Configures the ALCC pin.
[10] Alert Mode.
Alert functionality enabled. Pin
becomes logic output.
[01] Charge Complete Mode. Pin
becomes logic input and accepts
charge complete inverted signal
(e.g., from a charger) to set
accumulated charge register (C,D)
to FFFFh.
[00] ALCC pin disabled.
[11] Not allowed.
[10]
B[0] Shutdown Shut down analog section to
reduce ISUPPLY.
[0]
Power Down B[0]
Setting B[0] to 1 shuts down the analog parts of the
LTC2943, reducing the current consumption to less than
15μA (typical). The circuitry managing I2C communica-
tion remains operating and the values in the registers are
retained. Note that any charge flowing while B[0] is 1 is
not measured and any charge information below 1LSB of
the accumulated charge register is lost.
Alert/Charge Complete Configuration B[2:1]
The ALCC pin is a dual function pin configured by the
control register. By setting bits B[2:1] to [10] (default),
the ALCC pin is configured as an alert pin following the
SMBus protocol. In this configuration, the ALCC is pulled
low if one of the four measured quantities (charge, voltage,
current, temperature) exceeds its high or low threshold or
if the value of the accumulated charge register overflows
or underflows. An alert response procedure started by the
master resets the alert at the ALCC pin. If the configura-
tion of the ALCC pin is changed while it is pulled low due
to an alert condition, the part will continue to pull ALCC
low until a successful alert response procedure (ARA) has
been issued by the master. For further information see the
Alert Response Protocol section.
Setting the control bits B[2:1] to [01] configures the
ALCC pin as a digital input. In this mode, a low input on
the ALCC pin indicates to the LTC2943 that the battery
is full and the accumulated charge register is set to its
maximum, value FFFFh.
APPLICATIONS INFORMATION
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If neither the alert nor the charge complete functionality
is desired, bits B[2:1] should be set to [00]. The ALCC
pin is then disabled and should be tied to the supply of
the I2C bus with a 10k resistor.
Avoid setting B[2:1] to [11] as it enables the alert and the
charge complete modes simultaneously.
Choosing RSENSE
To achieve the specified precision of the coulomb counter,
the differential voltage between SENSE+ and SENSE– must
stay within ±50mV. With input signals up to 300mV the
LTC2943 will remain functional but the precision of the
coulomb counter is not guaranteed.
The required value of the external sense resistor, RSENSE,
is determined by the maximum input range of VSENSE and
the maximum current of the application:
RSENSE ≤
50mV
I
MAX
The choice of the external sense resistor value influences
the gain of the coulomb counter. A larger sense resistor
gives a larger differential voltage between SENSE+ and
SENSE– for the same current resulting in more precise
coulomb counting. The amount of charge represented by
the least significant bit (qLSB) of the accumulated charge
(registers C, D) is equal to:
qLSB = 0.340mAh•
50mΩ
R
SENSE
•
M
4096
or
qLSB = 0.340mAh•
50mΩ
R
SENSE
when the prescaler is set to its default value of M = 4096.
Note that 1mAh = 3.6C (coulomb).
Choosing RSENSE = 50mV/IMAX is not sufficient in
applications where the battery capacity (QBAT) is very large
compared to the maximum current (IMAX):
QBAT >IMAX •22Hours
For such low current applications with a large battery,
choosing RSENSE according to RSENSE = 50mV/IMAX can
lead to a qLSB smaller than QBAT/216 and the 16-bit accu-
mulated charge register may underflow before the battery
is exhausted or overflow during charge. Choose, in this
case, a maximum RSENSE of:
RSENSE ≤0.340mAh•216
Q
BAT
•50mΩ
In an example application where the maximum current is
IMAX = 100mA, calculating RSENSE = 50mV/IMAX would
lead to a sense resistor of 500mΩ. This gives a qLSB of
34μAh and the accumulated charge register can represent
a maximum battery capacity of QBAT = 34μAh•65535 =
2228mAh. If the battery capacity is larger, RSENSE must
be lowered. For example, RSENSE should be reduced to
150mΩ if a battery with a capacity of 7200mAh is used.
Choosing Coulomb Prescaler M B[5:3]
If the battery capacity (QBAT) is small compared to the
maximum current (IMAX) the prescaler value M should
be changed from its default value (4096).
In these applications with a small battery but a high maxi-
mum current, qLSB can get quite large with respect to the
battery capacity. For example, if the battery capacity is
100mAh and the maximum current is 1A, the standard
equation leads to choosing a sense resistor value of
50mΩ, resulting in:
qLSB = 0.340mAh=1224mC
The battery capacity then corresponds to only 294 qLSB
and less than 0.5% of the accumulated charge register
is utilized.
To preserve digital resolution in this case, the LTC2943
includes a programmable prescaler. Lowering the prescaler
factor M reduces qLSB to better match the accumulated
charge register to the capacity of the battery. The prescaling
factor M can be chosen between 1 and its default value
of 4096. The charge LSB then becomes:
qLSB = 0.34mAh•
50mΩ
R
SENSE
•
M
4096
APPLICATIONS INFORMATION
LTC2943
12
2943fa
For more information www.linear.com/LTC2943
To use as much of the range of the accumulated charge
register as possible the prescaler factor M should be
chosen for a given battery capacity QBAT and a sense
resistor RSENSE as:
M≥ 4096 •
Q
BAT
2
16
•0.340mAh
•
R
SENSE
50mΩ
M can be set to 1, 4, 16, ... 4096 by programming B[5:3]
of the control register as M = 22•(4 • B[5] + 2 • B[4] + B[3]) .
The default value is 4096.
In the above example of a 100mAh battery and an RSENSE
of 50mΩ, the prescaler should be programmed to
M = 64. The qLSB is then 5.313μAh and the battery capacity
corresponds to roughly 18821 qLSBs.
Figure 3 illustrates the best choice for prescaler value M
and the sense resistor as function of the ratio between
battery capacity (QBAT) and maximum current (IMAX). It
can be seen, that for high current applications with low
battery capacity the prescaler value should be reduced,
whereas in low current applications with a large battery
the sense resistor should be reduced with respect to its
default value of 50mV/IMAX.
ADC Mode B[7:6]
The LTC2943 features an ADC which measures either
voltage on SENSE– (battery voltage), voltage difference
between SENSE+ and SENSE– (battery current) or tem-
perature via an internal temperature sensor. The reference
voltage and clock for the ADC are generated internally.
The ADC has four different modes of operation as shown
in Table 3. These modes are controlled by bits B[7:6] of
the control register. At power-up, bits B[7:6] are set to
[00] and the ADC is in sleep mode.
A single conversion of the three measured quantities
is initiated by setting the bit B[7:6] to [01]. After three
conversions (voltage, current and temperature), the ADC
resets B[7:6] to [00] and goes back to sleep.
The LTC2943 is set to scan mode by setting B[7:6] to
[10]. In scan mode the ADC converts voltage, current,
then temperature, then sleeps for approximately 10 sec-
onds. It then reawakens automatically and repeats the
three conversions. The chip remains in scan mode until
reprogrammed by the host.
Programming B[7:6] to [11] sets the chip into automatic
mode where the ADC continuously performs voltage,
current and temperature conversions. The chip stays in
automatic mode until reprogrammed by the host.
Programming B[7:6] to [00] puts the ADC to sleep. If
control bits B[7:6] change within a conversion, the ADC
will complete the running cycle of conversions before
entering the newly selected mode.
A conversion of voltage requires 33ms (typical), and cur-
rent and temperature conversions are completed in 4.5ms
(typical). At the end of each conversion, the corresponding
registers are updated. If the converted quantity exceeds
the values programmed in the threshold registers, a flag
is set in the status register and the ALCC pin is pulled low
(if alert mode is enabled).
During ADC conversions additional currents are sunk from
SENSE+ and SENSE–, refer to the Electrical Characteristics
table for details.
APPLICATIONS INFORMATION
Figure 3. Choice of Sense Resistor and Prescaler as Function of Battery Capacity and Maximum Current
2943 F03
M = 1
0.005h QBAT/IMAX
0.08h 0.34h 1.4h 5.5h 22h
M = 4 M = 16 M = 64 M = 256 M = 1024 M = 4096
0.02h
RSENSE ≤50mV
IMAX
RSENSE ≤ 0.34mAh • 216
QBAT
• 50mΩ
LTC2943
13
2943fa
For more information www.linear.com/LTC2943
Alert Thresholds Registers (E,F,G,H,K,L,M,N,Q,R,S,
T,W,X)
For each of the measured quantities (battery charge,
voltage, current and temperature) the LTC2943 features
high and low threshold registers. At power-up, the high
thresholds are set to FFFFh while the low thresholds are set
to 0000h, with the effect of disabling them. All thresholds
can be programmed to a desired value via I2C. As soon
as a measured quantity exceeds the high threshold or
falls below the low threshold, the LTC2943 sets the cor-
responding flag in the status register and pulls the ALCC
pin low if alert mode is enabled via bits B[2:1].
Accumulated Charge Register (C,D)
The coulomb counting circuitry in the LTC2943 integrates
current through the sense resistor. The result of this charge
integration is stored in the 16-bit accumulated charge
register (registers C, D). As the LTC2943 does not know
the actual battery status at power-up, the accumulated
charge register (ACR) is set to mid-scale (7FFFh). If the
host knows the status of the battery, the accumulated
charge (C[7:0]D[7:0]) can be either programmed to the
correct value via I2C or it can be set after charging to FFFFh
(full) by pulling the ALCC pin low if charge complete mode
is enabled via bits B[2:1]. Note that before writing to the
accumulated charge registers, the analog section should
be temporarily shut down by setting B[0] to 1. In order to
avoid a change in the accumulated charge registers between
reading MSBs C[7:0] and LSBs D[7:0], it is recommended
to read them sequentially as shown in Figure 10.
Voltage Registers (I,J), and Voltage Threshold
Registers (K,L,M,N)
The result of the 14-bit ADC conversion of the voltage at
SENSE– is stored in the voltage registers (I, J).
From the result of the 16-bit voltage registers I[7:0]J[7:0]
the measured voltage can be calculated as:
VSENSE–=23.6V •
RESULT
h
FFFF
h
=23.6V •
RESULT
DEC
65535
Example 1: a register value I[7:0] = B0h and J[7:0] = 1Ch
corresponds to a voltage on SENSE– of:
VSENSE–=23.6V •
B01C
h
FFFF
h
=23.6V •
45084
DEC
65535 ≈16.235V
Example 2: To set a low level threshold for the battery
voltage of 7.2V, register M should be programmed to 4Eh
and register N to 1Ah.
Current Registers (O,P) and Current Threshold
Registers (Q,R,S,T)
The result of the current conversion is stored in the cur-
rent registers (O,P).
As the ADC resolution is 12 bits in current mode, the
lowest four bits of the combined current registers (O, P)
are always zero.
The ADC measures battery current by converting the volt-
age, VSENSE, across the sense resistor RSENSE. Depending
on whether the battery is being charged or discharged, the
measured voltage drop on RSENSE is positive or negative.
The result is stored in registers O and P in excess –32767
representation. O[7:0] = FFh, P[7:0] = FFh corresponds to
the full scale positive voltage 60mV. While O[7:0] = 00h,
P[7:0] = 00h corresponds to the full scale negative volt-
age –60mV. The battery current can be obtained from the
two byte register O[7:0]P[7:0] and the value of the chosen
sense resistor RSENSE:
IBAT =VSENSE
RSENSE
=60mV
RSENSE
•RESULTh– 7FFFh
7FFFh
=
60mV
RSENSE
•RESULTDEC – 32767
32767
Positive current is measured when the battery is charg-
ing and negative current is measured when the battery is
discharging.
APPLICATIONS INFORMATION
LTC2943
14
2943fa
For more information www.linear.com/LTC2943
Example 1: a register value of O[7:0] = A8h P[7:0] = 40h
together with a sense resistor RSENSE = 50mΩ corresponds
to a battery current:
IBAT =60mV
50mΩ•A840h– 7FFFh
7FFFh
=
60mV
50mΩ•43072 – 32767
32767 ≈ 377.3mA
The positive current result indicates that the battery is
being charged.
The values in the threshold register for the current mode
Q,R,S,T are also expressed in excess –32767 representa-
tion in the same manner as the current conversion result.
The alert after a current measurement is set if the result
is higher than the value stored in the high threshold reg-
isters Q,R or lower than the value stored in the low value
registers S,T.
Example 2: In an application, the user wants to get an
alert if the absolute current through the sense resistor,
RSENSE, of 50mΩ exceeds 1A. This is achieved by setting
the upper threshold IHIGH in register [Q,R] to 1A and the
lower threshold ILOW in register [S,T] to –1A. The formula
for IBAT leads to:
IHIGH(DEC) =1A •50mΩ
60mV •32767 +32767= 60073
ILOW (DEC) =–1A •50mΩ
60mV •32767 + 32767=5461
Leading the user to set Q[7:0] = EAh, R[7:0] = A9h for
the high threshold and S[7:0] = 15h and T[7:0] = 55h for
the low threshold.
Temperature Registers (U,V), and Temperature
Threshold Registers (W,X)
As the ADC resolution is 11 bits in temperature mode, the
lowest five bits of the combined temperature registers
(U, V) are always zero.
The actual temperature can be obtained from the two byte
register U[7:0]V[7:0] by:
T =510K • RESULTh
FFFF
h
=510K •
RESULT
DEC
65535
Example: a register value of U[7:0] = 96h, V[7:0] = 96h
corresponds to ~300K or ~27°C
A high temperature limit of 60°C is programmed by setting
register W to A7h. Note that the temperature threshold
register is a single byte register and only the eight MSBs
of the 11 bits temperature result are checked.
Effect of Differential Offset Voltage on Total Charge
Error
In battery gas gauges, an important parameter is the
differential offset (VOS) of the circuitry monitoring the
battery charge. Many coulomb counter devices perform
an analog to digital conversion of VSENSE, where VSENSE
is the voltage drop across the sense resistor, and ac-
cumulate the conversion results to infer charge. In such
an architecture, the differential offset VOS causes relative
charge error of VOS/VSENSE. For small VSENSE values VOS
can be the main source of error.
The LTC2943 performs the tracking of the charge with an
analog integrator. This approach allows to continuously
monitor the battery charge and significantly lowers the
error due to differential offset. The relative charge error
due to offset (CEOV) can be expressed by:
CEOV =VOS
VSENSE
2
As example, at a 1mV input signal, a differential voltage
offset VOS = 20µV results in a 2% error using digital
integration, whereas the error is only 0.04% (a factor of
50 times smaller!) using the analog integration approach
of LTC2943.
APPLICATIONS INFORMATION
LTC2943
15
2943fa
For more information www.linear.com/LTC2943
The reduction of the impact of the offset in LTC2943 can
be explained by its integration scheme depicted in Figure 2.
While positive offset accelerates the up ramping of the
integrator output from REFLO to REFHI, it slows the down
ramping from REFHI to REFLO thus the effect is largely
canceled as depicted below.
I2C Protocol
The LTC2943 uses an I2C/SMBus-compatible 2-wire
interface supporting multiple devices on a single bus.
Connected devices can only pull the bus lines low and
must never drive the bus high. The bus wires are externally
connected to a positive supply voltage via current sources
or pull-up resistors. When the bus is idle, all bus lines are
high. Data on the I2C bus can be transferred at rates of
up to 100kbit/s in standard mode and up to 400kbit/s in
fast mode.
Each device on the I2C/SMbus is recognized by a unique
address stored in that device and can operate as either a
transmitter or receiver, depending on the function of the
device. In addition to transmitters and receivers, devices
can also be classified as masters or slaves when perform-
ing data transfers. A master is the device which initiates a
data transfer on the bus and generates the clock signals to
permit that transfer. At the same time any device addressed
is considered a slave. The LTC2943 always acts as a slave.
Figure 4 shows an overview of the data transmission on
the I2C bus.
Start and Stop Conditions
When the bus is idle, both SCL and SDA must be high. A
bus master signals the beginning of a transmission with
a START condition by transitioning SDA from high to low
while SCL is high. When the master has finished com-
municating with the slave, it issues a STOP condition by
APPLICATIONS INFORMATION
Figure 4. Data Transfer Over I2C or SMBus
For input signals with an absolute value smaller than the
offset of the internal op amp, the LTC2943 stops integrat-
ing and does not integrate its own offset.
I2C/SMBus Interface
The LTC2943 communicates with a bus master using
a 2-wire interface compatible with I2C and SMBus. The
7-bit hard coded I2C address of the LTC2943 is 1100100.
The LTC2943 is a slave only device. The serial clock line
(SCL) is input only while the serial data line (SDA) is
bidirectional. The device supports I2C standard and fast
mode. For more details refer to the I2C Protocol section.
2943 F0B
INTEGRATOR
OUTPUT
REFHI
REFLO
TIME
WITH OFFSET
WITHOUT OFFSET
FASTER
UP RAMPING
SLOWER
DOWN RAMPING
SCL
SDA
START
CONDITION
STOP
CONDITION
ADDRESS R/W ACK DATA ACK DATA ACK
1 - 7 8 9
2943 F04
a6 - a0 b7 - b0 b7 - b0
1 - 7 8 9 1 - 7 8 9
P
S
LTC2943
16
2943fa
For more information www.linear.com/LTC2943
Figure 5. Writing FCh to the LTC2943 Control Register (B)
transitioning SDA from low to high while SCL is high. The
bus is then free for another transmission. When the bus
is in use, it stays busy if a repeated START (Sr) is gener-
ated instead of a STOP condition. The repeated START
(Sr) conditions are functionally identical to the START (S).
Write Protocol
The master begins a write operation with a START condition
followed by the seven bit slave address 1100100 and the
R/W bit set to zero, as shown in Figure 5. The LTC2943
acknowledges this by pulling SDA low and the master
sends a command byte which indicates which internal
register the master is to write. The LTC2943 acknowledges
and latches the command byte into its internal register
address pointer. The master delivers the data byte, the
LTC2943 acknowledges once more and latches the data
into the desired register. The transmission is ended when
the master sends a STOP condition. If the master contin-
ues by sending a second data byte instead of a stop, the
APPLICATIONS INFORMATION
LTC2943 acknowledges again, increments its address
pointer and latches the second data byte in the following
register, as shown in Figure 6.
Read Protocol
The master begins a read operation with a START condition
followed by the seven bit slave address 1100100 and the
R/W bit set to zero, as shown in Figure 7. The LTC2943
acknowledges and the master sends a command byte
which indicates which internal register the master is to
read. The LTC2943 acknowledges and then latches the
command byte into its internal register address pointer.
The master then sends a repeated START condition fol-
lowed by the same seven bit address with the R/W bit
now set to one. The LTC2943 acknowledges and sends
the contents of the requested register. The transmission
is ended when the master sends a STOP condition. If
the master acknowledges the transmitted data byte, the
LTC2943 increments its address pointer and sends the
contents of the following register as depicted in Figure 8.
Figure 6. Writing F001h to the LTC2943 Accumulated Charge
Register (C, D)
Figure 7. Reading the LTC2943 Status Register (A)
Figure 8. Reading the LTC2943 Voltage Register (I, J)
FROM MASTER TO SLAVE
SW
ADDRESS REGISTER DATA
FROM SLAVE TO MASTER
2943 F05
A: ACKNOWLEDGE (LOW)
A: NOT ACKNOWLEDGE (HIGH)
S: START CONDITION
P: STOP CONDITION
R: READ BIT (HIGH)
W: WRITE BIT (LOW)
A A A
0
1100100 01h FCh
0 0 0
P
SW
ADDRESS REGISTER DATA
2943 F06
A A A
0
1100100 02h F0h 01h
0 0 0 0
P
DATA A
SW
ADDRESS REGISTER Sr
2943 F07
A A ADDRESS
0
1100100 00h 1
0 0 1100100 0
P
R
1
A
01h
DATA
A
SW
ADDRESS REGISTER Sr
2943 F08
A A ADDRESS
0
1100100 08h 1
0 0 1100100 0
P
R
0
A
F1h
DATA
24h
DATA
A
1
A
LTC2943
17
2943fa
For more information www.linear.com/LTC2943
Alert Response Protocol
In a system where several slaves share a common interrupt
line, the master can use the alert response address (ARA)
to determine which device initiated the interrupt (Figure 9).
SDA pin to see if another device is sending an address at
the same time using standard I2C bus arbitration. If the
LTC2943 is sending a 1 and reads a 0 on the SDA pin on
the rising edge of SCL, it assumes another device with a
lower address is sending and the LTC2943 immediately
aborts its transfer and waits for the next ARA cycle to try
again. If transfer is successfully completed, the LTC2943
will stop pulling down the ALCC pin and will not respond
to further ARA requests until a new Alert event occurs.
PC Board Layout Suggestions
Keep all traces as short as possible to minimize noise and
inaccuracy. Use a 4-wire Kelvin sense connection for the
sense resistor, locating the LTC2943 close to the resistor
with short sense-traces to the SENSE+ and SENSE– pins.
Use wider traces from the resistor to the battery, load
and/or charger. Put the bypass capacitor close to SENSE+
and GND.
The master initiates the ARA procedure with a START
condition and the special 7-bit ARA bus address (0001100)
followed by the read bit (R) = 1. If the LTC2943 is as-
serting the ALCC pin in alert mode, it acknowledges and
responds by sending its 7-bit bus address (1100100)
and a 1. While it is sending its address, it monitors the
APPLICATIONS INFORMATION
Figure 9. LTC2943 Serial Bus SDA Alert Response Protocol
Figure 10. Reading the LTC2943 Accumulated Charge
Registers (C, D)
Figure 12. Kelvin Connection on Sense Resistor
Figure 11. ADC Single Conversion Sequence and Reading
of Voltage Registers (I,J)
S R
ALERT RESPONSE ADDRESS DEVICE ADDRESS
2943 F09
A
1
0001100 1100100
0 1
P
A
SW
ADDRESS REGISTER S
2943 F10
A A ADDRESS
0
1100100 02h 1
0 0 1100100 0
P
R
0
A
80h
DATA
01h
DATA
A
1
A
40ms
SW
ADDRESS REGISTER S
2943 F11
A A ADDRESS
0
1100100 08h 1
0 0 1100100 0
P
R
0
A
F1h
DATA
80h
DATA
A
1
A
SW
ADDRESS REGISTER DATA
A A
0
1100100 01h 4C
0 0
P
LTC2943
2943 F12
RSENSE TO BATTERY
TO
CHARGER/LOAD
3
2
1
6
7
8
45
C
LTC2943
18
2943fa
For more information www.linear.com/LTC2943
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698 Rev C)
3.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON TOP AND BOTTOM OF PACKAGE
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
1.65 ± 0.10
(2 SIDES)
0.75 ±0.05
R = 0.125
TYP
2.38 ±0.10
14
85
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
0.00 – 0.05
(DD8) DFN 0509 REV C
0.25 ± 0.05
2.38 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
1.65 ±0.05
(2 SIDES)2.10 ±0.05
0.50
BSC
0.70 ±0.05
3.5 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
LTC2943
20
2943fa
For more information www.linear.com/LTC2943
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
LINEAR TECHNOLOGY CORPORATION 2013
LT 0514 REV A • PRINTED IN USA
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1
6
7
9
2
3
10
4
8
RPROG*
19.6k
RSENSE
0.25Ω
IBAT = 500mA
VIN = 10V
CTIMER
0.1µF
MBRM120T3
SENSE
DRV
VCC
BAT
PROGTIMER
LTC1732-8.4
SEL
R2
1k
R1
1k
CHRG
ACPR
GND
C2
10µF
Q1
Si7135DP
SENSE+
ALCC
SDA
SCL
LTC2943
R4
2k
R3
2k
R5
2k
0.5A
LOAD
RSENSE
100mΩ
8.4V
Li-Ion
BATTERY
2943 TA02
SENSE–
+
GND
C3
1µF
VDD
3.3V
µP
C1
1µF
2-Cell 8.4V Linear Charger and Battery Gas Gauge
