LINER LTC2942CDCBTRMPBF Battery gas gauge with temperature, voltage measurement Datasheet

LTC2942
Battery Gas Gauge
with Temperature,
Voltage Measurement
FEATURES
DESCRIPTION
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The LTC®2942 measures battery charge state, battery
voltage and chip temperature in 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.
Battery voltage and on-chip temperature are measured
with an internal 14-bit No Latency ΔΣ™ ADC. The three
measured quantities (charge, voltage and temperature)
are stored in internal registers accessible via the onboard
SMBus/I2C interface.
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Indicates Accumulated Battery Charge and
Discharge
High Accuracy Analog Integration
ADC Measures Battery Voltage and Temperature
Integrated Temperature Sensor
High Side Sense
1% Voltage and Charge Accuracy
±50mV Sense Voltage Range
SMBus/I2C 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 Players
Cameras
GPS
The LTC2942 features programmable high and low thresholds for all three 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 LTC2942 requires only a single low value sense resistor to set the measured current range.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. No Latency ΔΣ is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Total Charge Error vs
Differential Sense Voltage
2.0
VSENSE+ = 3.6V
CHARGER
LOAD
0.1μF
SENSE+
I2C/SMBus
TO HOST
LTC2942
AL/CC
SDA
SENSE–
SCL
GND
RSENSE
100mΩ
+
1-CELL
Li-Ion
CHARGE ERROR (%)
1.5
1.0
0.5
0
–0.5
–1.0
2942 TA01a
–1.5
–2.0
0.1
1
10
100
VSENSE (mV)
2942 TA01b
2942f
1
LTC2942
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1, 2)
Supply Voltage (SENSE+) ............................. –0.3V to 6V
SCL, SDA, AL/CC ......................................... –0.3V to 6V
SENSE– .................................. –0.3V to (VSENSE+ + 0.3V)
Operating Ambient Temperature Range
LTC2942C ................................................ 0°C to 70°C
LTC2942I.............................................. –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
TOP VIEW
6 SENSE–
SENSE+ 1
GND 2
7
GND
5 AL/CC
4 SDA
SCL 3
DCB PACKAGE
6-LEAD (2mm × 3mm) PLASTIC DFN
TJMAX = 150°C, θJA = 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)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2942CDCB#TRMPBF
LTC2942CDCB#TRPBF
LDVN
6-Lead (2mm × 3mm) Plastic DFN
0°C to 70°C
LTC2942IDCB#TRMPBF
LTC2942IDCB#TRPBF
LDVN
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/
–40°C to 85°C
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Power Requirements
VSENSE+
ISUPPLY
Supply Voltage
Supply Current (Note 3)
2.7
5.5
V
70
100
μA
300
350
μA
420
μA
2.5
μA
1
μA
2.7
V
±50
mV
Battery Gas Gauge On, ADC Sleep
l
Battery Gas Gauge On, ADC Converting Voltage
l
Battery Gas Gauge On, ADC Converting Temperature l
350
Shutdown
l
Shutdown, VSENSE+ ≤ 4.2V
VUVLO
Undervoltage Lockout Threshold
VSENSE+ Falling
l
VSENSE+ – VSENSE–
l
2.5
2.6
Coulomb Counter
VSENSE
Sense Voltage Differential Input
Range
RIDR
Differential Input Resistance,
Across SENSE+ and SENSE–
(Note 8)
qLSB
Charge LSB (Note 4)
TCE
Total Charge Error (Note 5)
Prescaler M = 128 (Default), RSENSE = 50mΩ
10mV ≤ |VSENSE| ≤ 50mV DC
400
kΩ
0.085
mAh
±1
%
10mV ≤ |VSENSE| ≤ 50mV DC, VSENSE + ≤ 4.2V
l
±1.5
%
1mV ≤ |VSENSE| < 50mV DC (Note 8)
l
±3.5
%
2942f
2
LTC2942
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Voltage Measurement ADC
Resolution (No Missing Codes)
VFS
Full-Scale Voltage
ΔVLSB
Quantization Step of 14-Bit
Voltage ADC
TUEV
Voltage Total Unadjusted Error
(Note 8)
l
14
l
(Note 6)
Bits
6
V
366.2
μV
1
1.3
l
l
Gain
Gain Accuracy
VOS
Offset
INL
Integral Nonlinearity
l
tCONV
Conversion Time
l
Extrapolated from Measurements at 5.5V and 2.7V
±1
±1
%
%
1.3
%
±10
LSB
±4
LSB
15
ms
Temperature Measurement ADC
Resolution (No Missing Code)
(Note 8)
10
l
TFS
Full-Scale Temperature
ΔTLSB
Quantization Step of 10-Bit
Temperature ADC
(Note 6)
TUET
Temperature Total Unadjusted
Error
VSENSE+ ≥ 2.8V (Note 8)
tCONV
Conversion Time
Bits
600
K
0.586
K
l
±5
±3
K
K
l
15
ms
Digital Inputs and Digital Outputs
VITH
Logic Input Threshold, AL/CC,
SCL, SDA
l
VOL
Low Level Output Voltage, AL/CC, I = 3mA
SDA
l
IIN
Input Leakage, AL/CC, SCL, SDA
VIN = VSENSE+/2
CIN
Input Capacitance, AL/CC, SCL,
SDA
(Note 8)
tPCC
Minimum Charge Complete (CC)
Pulse Width
0.3 • VSENSE+
0.7 • VSENSE+
V
0.4
V
l
1
μA
l
10
pF
1
μs
I2C Timing Characteristics
fSCL(MAX)
Maximum SCL Clock Frequency
l
tBUF(MIN)
Bus Free Time Between Stop/Start
l
1.3
μs
tSU,STA(MIN) Minimum Repeated Start Set-Up
Time
l
600
ns
tHD,STA(MIN) Minimum Hold Time (Repeated)
Start Condition
l
600
ns
tSU,STO(MIN) Minimum Set-Up Time for Stop
Condition
l
600
ns
tSU,DAT(MIN) Minimum Data Setup Time Input
l
100
ns
400
900
kHz
2942f
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LTC2942
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
tHD,DATI(MIN) Minimum Data Hold Time Input
l
0
μs
tHD,DATO
Data Hold Time Output
l
0.3
0.9
μs
Data Output Fall Time
l
20 + 0.1 • CB
300
ns
tof
(Notes 7, 8)
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–
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 = 0.085mAh •
Note 5: Deviation of qLSB from its nominal value.
Note 6: The quantization step of the 14-bit ADC in voltage mode and
10-bit ADC in temperature mode is not to be mistaken with the LSB of the
combined 16-bit voltage registers (I, J) and 16-bit temperature registers
(M, N).
Note 7: CB = Capacitance of one bus line in pF (10pF ≤ CB ≤ 400pF). See
Voltage and Temperature Registers section for more information.
Note 8: Guaranteed by design, not subject to test.
50mΩ M
•
RSENSE 128
See Choosing RSENSE and Choosing Coulomb Counter Prescaler M section
for more information. 1mAh = 3.6C (Coulombs).
TIMING DIAGRAM
tof
SDA
tSU, DAT
tHD, DATO,
tHD, DATI
tSU, STA
tHD, STA
tBUF
tSU, STO
2942 F01
SCL
tHD, STA
START
CONDITION
REPEATED START
CONDITION
STOP
CONDITION
START
CONDITION
Figure 1. Definition of Timing on I2C Bus
2942f
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LTC2942
TYPICAL PERFORMANCE CHARACTERISTICS
Total Charge Error vs Differential
Sense Voltage
Total Charge Error vs Supply
Voltage
CHARGE ERROR (%)
1
0
1.00
0.75
0.75
0.50
0.50
0.25
0
–0.25
–1
VSENSE+ = 2.7V
VSENSE+ = 4.2V
–3
0.1
1
10
100
–0.75
–1.00
2.5
3.0
3.5
4.0 4.5
5.0
VSENSE+ (V)
5.5
2942 G01
6.0
ISHUTDOWN (μA)
TA = 25°C
TA = –40°C
TA = 85°C
4.0 4.5
5.0
VSENSE+ (V)
5.5
6.0
0
2.5
3.0
3.5
4.0 4.5
5.0
VSENSE+ (V)
5.5
2942 G04
6.0
6
TA = 85°C
4
2
0
TA = –45°C
–2
–4
–6
TA = 25°C
–8
–10
2.5
3.0
3.5
4.0 4.5
5.0
VSENSE– (V)
2942 G05
Voltage Measurement ADC
Integral Nonlinearity
5.5
6.0
2942 G06
Temperature Error vs Temperature
1.0
3
TA = 85°C
TEMPERATURE ERROR (°C)
2
0.5
INL (VLSB)
ISUPPLY (μA)
1.0
50
3.5
100
8
0.5
3.0
75
10
1.5
40
2.5
25
0
50
TEMPERATURE (°C)
Voltage Measurement ADC
Total Unadjusted Error
2.0
TA = 25°C
TA = –40°C
TA = 85°C
60
–25
2942 G03
Shutdown Supply Current vs
Supply Voltage
100
70
–1.00
–50
VSENSE = –50mV
VSENSE = –10mV
2942 G02
Supply Current vs Supply Voltage
80
–0.25
–0.75
VSENSE = –50mV
VSENSE = –10mV
VSENSE (mV)
90
0
–0.50
–0.50
–2
0.25
TOTAL UNADJUSTED ERROR (mV)
CHARGE ERROR (%)
2
Total Charge Error vs Temperature
1.00
CHARGE ERROR (%)
3
0
TA = –40°C
TA = 25°C
–0.5
1
0
–1
–2
–1.0
2.5
3.0
3.5
4.0 4.5 5.0
VSENSE– (V)
5.5
6.0
2942 G07
–3
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
2942 G08
2942f
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LTC2942
PIN FUNCTIONS
SENSE+ (Pin 1): Positive Current Sense Input and Power
Supply. Connect to the load/charger side of the sense
resistor. VSENSE+ 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 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 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. SENSE– is also
the input for the ADC in voltage measurement mode.
BLOCK DIAGRAM
LTC2942
1
SENSE+
VSUPPLY
COULOMB COUNTER
REF
TEMPERATURE
SENSOR
6
2
SENSE–
MUX
CC
CLK
REFERENCE
GENERATOR
OSCILLATOR
REF+
CLK
IN
ACCUMULATED
CHARGE
REGISTER
AL
I2C/
SMBus
AL/CC
SCL
SDA
ADC
5
3
4
DATA AND
CONTROL
REGISTERS
REF–
GND
2942 BD
2942f
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LTC2942
OPERATION
Overview
The LTC2942 is a battery gas gauge device designed for
use with single Li-Ion cells and other battery types with a
terminal voltage at 2.7V to 5.5V. It measures battery charge
and discharge, battery voltage and chip temperature.
A precision coulomb counter integrates current through a
sense resistor between the battery’s positive terminal and
the load or charger. Battery voltage and on-chip temperature
are measured with an internal 14-bit/10-bit ADC.
Coulomb Counter
Charge is the time integral of current. The LTC2942 measures battery current by monitoring the voltage developed
across a sense resistor and then integrates this information
to infer charge. The differential voltage between SENSE+
and SENSE– is applied to an auto-zeroed differential analog
integrator to convert the measured current to charge.
When the integrator output ramps to REFHI or REFLO
levels, switches S1, S2, S3 and S4 toggle to reverse the
ramp direction. By observing the condition of the switches
and the ramp direction, polarity is determined.
CHARGER
LOAD
1
BATTERY
The LTC2942 includes a 14-bit No Latency ΔΣ analog-todigital converter, with internal clock and voltage reference
circuits.
The ADC can either be used to monitor the battery voltage
at SENSE– or to convert the output of the on-chip temperature sensor. The sensor generates a voltage proportional to
temperature with a slope of 2.5mV/K resulting in a voltage
of 750mV at 27°C.
Conversion of either temperature or voltage is triggered
by setting the control register via the I2C interface. The
LTC2942 features an automatic mode where a voltage and
a temperature conversion are executed every two seconds.
At the end of each conversion the corresponding registers
are updated and the converter goes to sleep to minimize
quiescent current.
+
CONTROL
LOGIC
S1
–
–
S2
RSENSE
IBAT
Voltage and Temperature ADC
REFHI
VCC
SENSE+
A programmable prescaler effectively increases integration
time by a factor M programmable from 1 to 128. 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.
S3
6
+
2
SENSE–
M
PRESCALER
+
+
S4
GND
ACR
POLARITY
DETECTION
REFLO
–
2942 F02
Figure 2. Coulomb Counter Section of the LTC2942
2942f
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LTC2942
OPERATION
Power-Up Sequence
When SENSE+ rises above a threshold of approximately
2.5V, the LTC2942 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 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 pre-scaling factor M
is set to 128.
APPLICATIONS INFORMATION
I2C/SMBus Interface
The LTC2942 communicates with a bus master using a
2-wire interface compatible with I2C and SMBus. The 7-bit
hard-coded I2C address of the LTC2942 is 1100100.
The LTC2942 is a slave-only device. Therefore the serial
clock line (SCL) is an 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.
The sixteen internal registers are organized as shown in
Table 1.
Table 1. Register Map
ADDRESS
NAME REGISTER DESCRIPTION
R/W
DEFAULT
00h
A
Status
R
See Below
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
Internal Registers
06h
G
Charge Threshold Low MSB
R/W
00h
The LTC2942 integrates current through a sense resistor,
measures battery voltage and temperature and stores the
results in internal 16-bit registers accessible via I2C. High
and low limits can be programmed for each measurement
quantity. The LTC2942 continuously monitors these limits
and sets a flag in the onboard status register when a limit
is exceeded. If the alert mode is enabled, the AL/CC pin
pulls low.
07h
H
Charge Threshold Low LSB
R/W
00h
08h
I
Voltage MSB
R
XXh
09h
J
Voltage LSB
R
XXh
0Ah
K
Voltage Threshold High
R/W
FFh
0Bh
L
Voltage Threshold Low
R/W
00h
0Ch
M
Temperature MSB
R
XXh
0Dh
N
Temperature LSB
R
XXh
0Eh
O
Temperature Threshold High
R/W
FFh
0Fh
P
Temperature Threshold Low
R/W
00h
R = Read, W = Write, XX = unknown
2942f
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LTC2942
APPLICATIONS INFORMATION
Status Register (A)
The status of the charge, voltage and temperature alerts
is reported in the status register shown in Table 2.
The hard-coded bit A[7] of the status register enables the
host to distinguish the LTC2942 from the pin compatible
LTC2941, allowing the same software to be used with
both devices.
Table 2. Status Register A (Read only)
BIT
NAME
A[7] Chip Identification
OPERATION
DEFAULT
0: LTC2942
1: LTC2941
0
A[6] Reserved
0
A[5] Accumulated Charge Indicates that the value of the
Overflow/Underflow 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
dropped below the charge
threshold low limit.
0
A[1] Voltage Alert
Indicates one of the battery
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.
X
Control Register (B)
The operation of the LTC2942 is controlled by programming the control register. Table 3 shows the organization
of the 8-bit control register B[7:0].
Table 3. Control Register B
All status register bits except A[7] are cleared after being
read by the host, if the conditions which set these bits
have been removed.
As soon as one of the three measured quantities exceeds
the programmed limits, the corresponding bit A[4], A[3],
A[2] or A[1] in the status register is set.
Bit A[5] is set if the LTC2942’s accumulated charge registers
(ACR) overflows or underflows. In these cases, the ACR
stays at FFFFh or 0000h and does not roll over.
The undervoltage lockout (UVLO) bit of the status register
A[0] is set if, during operation, the voltage on SENSE+
pin drops below 2.7V 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+ < 2.7V.
BIT
NAME
OPERATION
Default
B[7:6] ADC Mode
[11] Automatic Mode.
Performs voltage and temperature
conversion every second.
[10] Manual Voltage Mode.
Performs single voltage
conversion, then sleeps.
[01] Manual Temperature Mode.
Performs single temperature
conversion, then sleeps.
[00] Sleep.
[00]
B[5:3] Prescaler M
Sets coulomb counter prescaling
factor M between 1 and 128.
Default is 128.
M = 2(4 • B[5] + 2 • B[4] + B[3])
[111]
B[2:1] AL/CC Configure Configures the AL/CC pin.
[10] Alert Mode.
Alert functionality enabled.
Pin becomes logic output.
[01] Charge Complete Mode.
Pin becomes logic input and
accepts “charge complete” signal
(e.g., from a charger) to set
accumulated charge register (C,D)
to FFFFh.
[00] AL/CC pin disabled.
[11] Not allowed.
B[0]
Shutdown
Shut down analog section to
reduce ISUPPLY.
[10]
[0]
Power Down B[0]
Setting B[0] to 1 shuts down the analog parts of the
LTC2942, reducing the current consumption to less than
1μA. All analog circuits are inoperative while the values
in the registers are retained. Note that any charge flowing
while B[0] is 1 is not measured and the charge information
below 1LSB of the accumulated charge register is lost.
2942f
9
LTC2942
APPLICATIONS INFORMATION
Alert/Charge Complete Configuration B[2:1]
The AL/CC pin is a dual function pin configured by the
control register. By setting bits B[2:1] to [10] (default)
the AL/CC pin is configured as an alert pin following the
SMBus protocol. In this configuration the AL/CC pin is a
digital output and is pulled low if one of the three measured quantities (charge, voltage, 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
AL/CC pin. For further information see the Alert Response
Protocol section.
Setting the control bits B[2:1] to [01] configures the AL/CC
pin as a digital input. In this mode, a high input on the
AL/CC pin communicates to the LTC2942 that the battery
is full and the accumulated charge register is set to its
maximum value FFFFh. The AL/CC pin would typically
be connected to the “charge complete” output from the
battery charger circuitry.
If neither the alert nor the charge complete functionality
is desired, bits B[2:1] should be set to [00]. The AL/CC
pin is then disabled and should be tied to GND.
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. For differential input signals up to
±300mV the LTC2942 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
IMAX
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 which results in more precise
coulomb counting. Thus the amount of charge represented
by the least significant bit (qLSB) of the accumulated charge
(registers C, D) is equal to:
qLSB = 0.085mAh •
50mΩ M
•
RSENSE 128
qLSB = 0.085mAh •
50mΩ
RSENSE
or
when the prescaler is set to its default value of M = 128.
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 • 5.5 Hours
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 accumulated charge register may underflow before the battery
is exhausted or overflow during charge. Choose, in this
case, a maximum RSENSE of:
RSENSE ≤
0.085mAh • 216
• 50mΩ
QBAT
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
8.5μAh and the accumulated charge register can represent
a maximum battery capacity of QBAT = 8.5μAh • 65535 =
557mAh. If the battery capacity is larger, RSENSE must be
lowered. For example, RSENSE must be reduced to 150mΩ
if a battery with a capacity of 1800mAh is used.
Choosing Coulomb Counter Prescaler M B[5:3]
If the battery capacity (QBAT) is very small compared to
the maximum current (IMAX) (QBAT < IMAX • 0.1 Hours)
the prescaler value M should be changed from its default
value (128).
In these applications with a small battery but a high
maximum current, qLSB can get quite large with respect
2942f
10
LTC2942
APPLICATIONS INFORMATION
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 = 0.085mAh = 306mC
The battery capacity then corresponds to only 1176 qLSBs
and less than 2% of the accumulated charge register is
utilized.
To preserve digital resolution in this case, the LTC2942
includes a programmable prescaler. Lowering the prescaler factor M allows reducing 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 128. The charge LSB then becomes:
qLSB = 0.085mAh •
50mΩ M
•
RSENSE 128
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≥128 •
RSENSE
216 • 0.085mAh 50mΩ
QBAT
•
M can be set to 1, 2, 4, 8, … 128 by programming B[5:3] of
the control register as M = 2(4 • B[5] + 2 • B[4] + B[3]). The default
value after power up is M = 128 = 27 (B[5:3] = 111).
In the above example of a 100mAh battery and an RSENSE
of 50mΩ, the prescaler should be programmed to M = 4.
The qLSB then becomes 2.656μAh and the battery capacity
corresponds to roughly 37650 qLSBs.
Note that the internal digital resolution of the coulomb
counter is higher than indicated by qLSB. The digitized
charge qINTERNAL is M • 8 times smaller than qLSB. qINTERNAL
is typically 299μAs for a 50mΩ sense resistor.
ADC Mode B[7:6]
The LTC2942 features an ADC which measures either
voltage on SENSE– (battery voltage) or temperature 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 voltage conversion is initiated by setting the bits
B[7:6] to [10]. A single temperature conversion is started
by setting bits B[7:6] to [01]. After a single voltage or
temperature conversion, the ADC resets B[7:6] to [00]
and goes to sleep.
The LTC2942 also offers an automatic scan mode where
the ADC converts voltage, then temperature, then sleeps
for approximately two seconds before repeating the voltage
and temperature conversions. The LTC2942 is set to this
automatic mode by setting B[7:6] to [11] and stays in this
mode until B[7:6] are 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 current conversion before entering the
newly selected mode.
A conversion of either voltage or temperature requires 10ms
conversion time (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 AL/CC
pin is pulled low (if alert mode is enabled).
During a voltage conversion, the SENSE– pin is connected
through a small resistor to a sampling circuit with an
equivalent resistance of 2MΩ, leading to a mean input
current of I = VSENSE–/2MΩ.
Accumulated Charge Register (C,D)
The coulomb counter of the LTC2942 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 LTC2942 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
AL/CC pin high if charge complete mode is enabled via
bits B[2:1]. Before writing the accumulated charge regis2942f
11
LTC2942
APPLICATIONS INFORMATION
ters, the analog section should be 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 and Temperature Registers (I, J),(M, N)
The result of the 14-bit ADC conversion of the voltage at
SENSE– is stored in the voltage registers (I, J), whereas
the temperature measurement result is stored in the temperature registers (M, N). The voltage and temperature
registers are read only.
As the ADC resolution is 14-bit in voltage mode and 10-bit
in temperature mode, the lowest two bits of the combined
voltage registers (I, J) and the lowest six bits of the
combined temperature registers (M, N) are always zero.
From the result of the 16-bit voltage registers I[7:0]J[7:0]
the measured voltage can be calculated as:
VSENSE – = 6V •
RESULTDEC
RESULTh
= 6V •
FFFFh
65535
Example: a register value of I[7:0] = B0h and J[7:0] = 1Ch
corresponds to a voltage on SENSE– of:
VSENSE – = 6 V •
45084DEC
B01Ch
= 6V •
≈ 4.12776V
FFFFh
65535
The actual temperature can be obtained from the two byte
register C[7:0]D[7:0] by:
T = 600K •
RESULTDEC
RESULTh
= 600K •
FFFFh
65535
Example: a register value of C[7:0] = 80h D[7:0] = 00h
corresponds to 300K or 27°C.
Threshold Registers (E, F, G, H, K, L, O, P)
For each of the measured quantities (battery charge, voltage and temperature) the LTC2942 features a high and a
low threshold registers. At power-up, the high thresholds
are set to FFFFh while the low thresholds are set to 0000h.
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 LTC2942
sets the corresponding flag in the status register and
pulls the AL/CC pin low if alert mode is enabled via bits
B[2:1]. Note that the voltage and temperature threshold
registers are single byte registers and only the 8 MSBs of
the corresponding quantity are checked. To set a low level
threshold for the battery voltage of 3V, register L should
be programmed to 80h; a high temperature limit of 60°C
is programmed by setting register O to 8Eh.
I2C Protocol
The LTC2942 uses an I2C/SMBus compatible 2-wire opendrain interface supporting multiple devices and masters
on a single bus. The connected devices can only pull the
bus wires low and they never drive the bus high. The bus
wires must be externally connected to a positive supply
voltage via a current source or pull-up resistor. When the
bus is idle, both SDA and SCL 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 performing 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 LTC2942 always acts
as a slave.
Figure 3 shows an overview of the data transmission for
fast and standard mode 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 communicating with the slave, it issues a STOP condition by
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 generated
instead of a STOP condition. The repeated START (Sr)
conditions are functionally identical to the START (S).
2942f
12
LTC2942
APPLICATIONS INFORMATION
Data Transmission
the master sends a command byte which indicates which
internal register the master is to write. The LTC2942 acknowledges and latches the command byte into its internal
register address pointer. The master delivers the data byte,
the LTC2942 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
continues by sending a second data byte instead of a stop,
the LTC2942 acknowledges again, increments its address
pointer and latches the second data byte in the following
register, as shown in Figure 5.
After a START condition, the I2C bus is considered busy
and data transfer begins between a master and a slave. As
data is transferred over I2C in groups of nine bits (eight
data bits followed by an acknowledge bit), each group
takes nine SCL cycles. The transmitter releases the SDA
line during the acknowledge clock pulse and the receiver
issues an acknowledge (ACK) by pulling SDA low or leaves
SDA high to indicate a not acknowledge (NAK) condition.
Change of data state can only happen while SCL is low.
Write Protocol
Read 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 4. The
LTC2942 acknowledges this by pulling SDA low and then
SDA
a6 - a0
SCL
1-7
8
9
ADDRESS
R/W
ACK
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 6. The LTC2942
b7 - b0
b7 - b0
1-7
8
9
1-7
8
9
S
P
DATA
ACK
DATA
ACK
START
CONDITION
STOP
CONDITION
Figure 3. Data Transfer Over I2C or SMBus
S
ADDRESS
W
A
REGISTER
A
DATA
A
1100100
0
0
01h
0
FCh
0
2942 F03
P
2942 F04
FROM MASTER TO SLAVE
A: ACKNOWLEDGE (LOW)
A: NOT ACKNOWLEDGE (HIGH)
FROM SLAVE TO MASTER
S: START CONDITION
P: STOP CONDITION
R: READ BIT (HIGH)
W: WRITE BIT (LOW)
Figure 4. Writing FCh to the LTC2942 Control Register (B)
S
ADDRESS
W
A
REGISTER
A
DATA
A
DATA
A
1100100
0
0
02h
0
F0h
0
01h
0
P
S
ADDRESS
W
A
REGISTER
A
1100100
0
0
00h
0
S
ADDRESS
R
A
DATA
A
1100100
1
0
01h
1
2942 F05
2942 F06
Figure 5. Writing F001h to the LTC2942
Accumulated Charge Register (C, D)
S
ADDRESS
W
A
1100100
0
0
P
Figure 6. Reading the LTC2942 Status Register (A)
REGISTER
A
08h
0
S
ADDRESS
1100100
R
A
DATA
A
DATA
A
1
0
F1h
0
24h
1
P
2942 F07
Figure 7. Reading the LTC2942 Voltage Register (I, J)
2942f
13
LTC2942
APPLICATIONS INFORMATION
acknowledges and then the master sends a command
byte which indicates which internal register the master is
to read. The LTC2942 acknowledges and then latches the
command byte into its internal register address pointer. The
master then sends a repeated START condition followed
by the same seven bit address with the R/W bit now set
to one. The LTC2942 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 LTC2942
increments its address pointer and sends the contents of
the following register as depicted in Figure 7.
ing 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 LTC2942 immediately aborts its transfer
and waits for the next ARA cycle to try again. If transfer
is successfully completed, the LTC2942 will stop pulling
down the AL/CC 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 LTC2942 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 (see Figure 11). Put the bypass capacitor
close to SENSE+ and GND.
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 8).
TO
CHARGER/LOAD
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 LTC2942 is asserting
the AL/CC 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 SDA pin to see
if another device is sending an address at the same time
using standard I2C bus arbitration. If the LTC2942 is send-
S
RSENSE
6
1
C
2
TO BATTERY
LTC2942
5
4
3
2942 F10
Figure 11. Kelvin Connection on Sense Resistor
ALERT RESPONSE ADDRESS
R
A
DEVICE ADDRESS
A
0001100
1
0
11001001
1
P
2942 F08
Figure 8. LTC2942 Serial Bus SDA Alert Response Protocol
S ADDRESS W A REGISTER A DATA P
1100100 0 0
01h
0
S ADDRESS W A REGISTER A S ADDRESS R A DATA A DATA A P
10ms
1100100 0 0
BC
08h
0
1100100 1 0 F1h 0 80h 1
2942 F09
Figure 9. Voltage Conversion Sequence
S
ADDRESS
W
A
REGISTER
A
1100100
0
0
02h
0
S
ADDRESS
R
A
DATA
A
DATA
A
1100100
1
0
80h
0
01h
1
P
2942 F10
Figure 10. Reading the LTC2942 Accumulated Charge Registers (C, D)
2942f
14
LTC2942
PACKAGE DESCRIPTION
DCB Package
6-Lead Plastic DFN (2mm × 3mm)
(Reference LTC DWG # 05-08-1715)
0.70 p0.05
3.55 p0.05
1.65 p0.05
(2 SIDES)
2.15 p0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
1.35 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
2.00 p0.10
(2 SIDES)
R = 0.05
TYP
3.00 p0.10
(2 SIDES)
0.40 p 0.10
4
6
1.65 p 0.10
(2 SIDES)
PIN 1 NOTCH
R0.20 OR 0.25
s 45o CHAMFER
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
3
0.200 REF
0.75 p0.05
1
(DCB6) DFN 0405
0.25 p 0.05
0.50 BSC
1.35 p0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (TBD)
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 THE
TOP AND BOTTOM OF PACKAGE
2942f
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC2942
TYPICAL APPLICATION
Single Cell Lithium-Ion Coulomb Counter with Battery Charger for Charge and Discharge Currents of up to 500mA
4
VIN
5V
VCC
BAT
500mA
3
LTC4057-4.2
(CHARGER)
1μF
5
2k
LOAD
0.1μF
3.3V
PROG SHDN
GND
2k
1
VDD
μP
2
2k
2k
1
SENSE+
LTC2942
5
AL/CC
4
6
SDA
SENSE–
3
SCL
GND
RSENSE
100mΩ
+
1-CELL
Li-Ion
2
2942 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
Battery Gas Gauges
LTC2942-1
Battery Gas Gauge with I2C Interface and Voltage and
Temperature ADC; Integrated Sense Resistor
2.7V to 5.5V Operation, 14-Bit Δ∑-ADC, Pin Compatible with LTC2941-1
LTC2941
Battery Gas Gauge with I2C Interface
2.7V to 5.5V Operation, Pin Compatible with LTC2942
LTC2941-1
Battery Gas Gauge with I2C Interface and Integrated
2.7V to 5.5V Operation, Pin Compatible with LTC2942-1
50mΩ Sense Resistor
LTC4150
Coulomb Counter/Battery Gas Gauge
2.7V to 8.5V Operation, 10-Pin MSOP Package
Lithium-Ion Battery Charger in ThinSOT™
Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed
Battery Chargers
LTC1734
LTC4002
Switch Mode Lithium-Ion Battery Charger
Standalone, 4.7V ≤ VIN ≤ 24V, 500kHz Frequency
LTC4052
Monolithic Lithium-Ion Battery Pulse Charger
No Blocking Diode or External Power FET Required, ≤1.5A Charge Current
LTC4053
USB Compatible Monolithic Li-Ion Battery Charger
Standalone Charger with Programmable Timer, Up to 1.25A Charge Current
LTC4057
Lithium-Ion Linear Battery Charger
Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package
LTC4058
Standalone 950mA Lithium-Ion Charger in DFN
C/10 Charge Termination, Battery Kelvin Sensing, ±7% Charge Accuracy
LTC4059
900mA Linear Lithium-Ion Battery Charger
2mm × 2mm DFN Package, Thermal Regulation, Charge Current Monitor
Output
LTC4061
Standalone Linear Li-Ion Battery Charger with
Thermistor Input
4.2V, ±0.35% Float Voltage, Up to 1A Charge Current, 3mm × 3mm DFN
Package
LTC4063
Li-Ion Charger with Linear Regulator
Up to 1A Charge Current, 100mA, 125mV LDO, 3mm × 3mm DFN Package
LTC4088
High Efficiency Battery Charger/USB Power Manager
Maximizes Available Power from USB Port, Bat-Track™, Instant-On Operation,
1.5A Max Charge Current, 180mΩ Ideal Diode with <50mΩ Option,
3.3V/25mA Always-On LDO, 4mm × 3mm DFN-14 Package
ThinSOT and Bat-Track are trademarks of Linear Technology Corporation.
2942f
16 Linear Technology Corporation
LT 0210 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2010
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