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PDF LTC2941 Data sheet ( Hoja de datos )
| Número de pieza | LTC2941 | |
| Descripción | Battery Gas Gauge | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Indicates Accumulated Battery Charge and
Discharge
n High Accuracy Analog Integration
n High Side Sense
n 1% Charge Accuracy
n ±50mV Sense Voltage Range
n SMBus/I2C Interface
n Configurable Alert Output/Charge Complete Input
n 2.7V to 5.5V Operating Range
n Quiescent Current Less Than 100µA
n Small 6-Pin 2mm × 3mm DFN and 8-Lead
MSOP Packages
Applications
n Low Power Handheld Products
n Cellular Phones
n MP3 Player
n Cameras
n GPS
LTC2941
Battery Gas Gauge
with I2C Interface
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/I2C 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 and
ThinSOT and Bat-Track are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Typical Application
CHARGER
I2C/SMBus
TO HOST
SENSE+
LTC2941
AL/CC
SDA SENSE–
SCL
GND
RSENSE
100mΩ
+ 1-CELL
Li-Ion
2941 TA01a
LOAD
0.1µF
Total Charge Error vs
Differential Sense Voltage
2.0
VSENSE+ = 3.6V
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
0.1
1 10
VSENSE (mV)
100
2941 TA01b
For more information www.linear.com/LTC2941
2941fb
1
1 page  
Typical Performance Characteristics
LTC2941
Total Charge Error
vs Differential Sense Voltage
3
2
1
0
–1
–2
–3
0.1
VSENSE+ = 2.7V
VSENSE+ = 4.2V
1 10 100
VSENSE (mV)
2941 G01
Total Charge Error
vs Supply Voltage
1.00
0.75
0.50
0.25
0
–0.25
–0.50
–0.75
–1.00
VSENSE = –50mV
VSENSE = –10mV
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VSENSE+ (V)
2941 G02
Total Charge Error vs Temperature
1.00
0.75
0.50
0.25
0
–0.25
–0.50
–0.75
–1.00
–50 –25
VSENSE = –50mV
VSENSE = –10mV
0 25 50
TEMPERATURE (°C)
75
100
2941 G03
Supply Current vs Supply Voltage
100
TA = 25°C
90
TA = –40°C
TA = 85°C
80
Shutdown Supply Current
vs Supply Voltage
2.0
1.5
70 1.0
60
50
40
2.5 3.0
3.5 4.0 4.5 5.0
VSENSE+ (V)
5.5 6.0
2941 G04
0.5
TA = 25°C
TA = –40°C
TA = 85°C
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VSENSE+ (V)
2941 G05
For more information www.linear.com/LTC2941
2941fb
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5 Page 
LTC2941
Applications Information
be chosen for a given battery capacity QBAT and a sense
resistor RSENSE as:
M ≥ 128
•
216
•
QBAT
0.085mAh
•
RSENSE
50mΩ
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 a 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 smaller than qLSB. qINTERNAL is
typically 299µAs for a 50mΩ sense resistor.
VBAT Alert B[7:6]
tThhee vVoBltAaTgealearttSfEuNncStEio–n.
allows the
If enabled,
LTC2941
a drop of
to monitor
the voltage
at the SENSE– pin below a preset threshold is detected
and bit A[1] in the status register is set. If the alert mode
is enabled by setting B[2] to one, an alert is generated at
the AL/CC pin. The threshold for the VBAT alert function
is selectable according to Table 3.
Accumulated Charge Registers (C, D)
The coulomb counter of the LTC2941 integrates current
through the sense resistor. The 16-bit result of this charge
integration is stored in the accumulated charge registers
C and D. As the LTC2941 does not know the actual battery
status after initial power-up, the accumulated charge is
set to mid-scale (7FFFh). If the host knows the status of
the battery , the accumulated charge registers C[7:0] and
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
registers, 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 8.
Threshold Registers (E, F), (G, H)
For battery charge, the LTC2941 features a high and a
low threshold register. At power-up the high threshold
is set to FFFFh while the low threshold is set to 0000h.
Both thresholds can be programmed to a desired value via
I2C. As soon as the accumulated charge exceeds the high
threshold or falls below the low threshold, the LTC2941
sets the corresponding flag in the status register and pulls
the AL/CC pin low if alert mode is enabled.
I2C Protocol
The LTC2941 uses an I2C/SMBus compatible 2-wire open-
drain 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 should be externally connected to a positive sup-
ply 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 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 LTC2941 always acts as a slave.
Figure 4 shows an overview of the data transmission on
the I2C bus.
For more information www.linear.com/LTC2941
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| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LTC2941.PDF ] | |
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