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PDF LTC2942-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC2942-1 | |
| Descripción | 1A Battery Gas Gauge | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Indicates Accumulated Battery Charge and
Discharge
n SMBus/I2C Interface
n Integrated 50mΩ High Side Sense Resistor
n ±1A Sense Current Range
n High Accuracy Analog Integration
n ADC Measures Battery Voltage and Temperature
n Integrated Temperature Sensor
n 1% Voltage and Charge Accuracy
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 package
Applications
n Low Power Handheld Products
n Cellular Phones
n MP3 Players
n Cameras
n GPS
LTC2942-1
1A Battery Gas Gauge with
Internal Sense Resistor and
Temperature/Voltage
Measurement
Description
The LTC®2942-1 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 an internal 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 ∆Σ™
ADC. The three measured quantities (charge, voltage and
temperature) are stored in internal registers accessible via
the onboard SMBus/I2C interface.
The LTC2942-1 features programmable high and low
thresholds for all three measured quantities. If a pro-
grammed threshold is exceeded, the device communicates
an alert using either the SMBus alert protocol or by setting
a flag in the internal status register.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
No Latency ∆Σ, 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+
LTC2942-1
AL/CC
SDA
SENSE–
SCL
GND
LOAD
0.1µF
+ 1-CELL
Li-Ion
29421 TA01a
Total Charge Error vs Sense Current
1.00
VSENSE+ = 3.6V
0.75
0.50
0.25
0
–0.25
–0.50
–0.75
–1.00
1
10 100
|ISENSE| (mA)
1000
29421 TA01b
29421f
1 page  
Typical Performance Characteristics
Total Charge Error
vs Sense Current
1.00
0.75
0.50
0.25
0
–0.25
–0.50
–0.75
–1.00
1
VSENSE+ = 2.7V
VSENSE+ = 4.2V
10 100
|ISENSE| (mA)
1000
29421 G01
Supply Current vs Supply Voltage
100
TA = 25°C
90
TA = –40°C
TA = 85°C
80
Total Charge Error
vs Supply Voltage
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
2.5
3
|ISENSE| = 1A
|ISENSE| = 200mA
3.5 4 4.5 5 5.5 6
VSENSE+ (V)
29421 G02
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
29421 G04
Voltage Measurement ADC
Integral Nonlinearity
1.0
TA = 85°C
0.5
0.5
0
2.5 3.0
3.5 4.0 4.5
TA = 25°C
TA = –40°C
TA = 85°C
5.0 5.5 6.0
VSENSE+ (V)
29421 G05
Temperature Error vs Temperature
3
2
1
0
TA = –40°C
–0.5 TA = 25°C
0
–1
–2
–1.0
2.5 3.0
3.5 4.0 4.5 5.0
VSENSE– (V)
5.5 6.0
29421 G07
–3
–50 –25
0
25 50
TEMPERATURE (°C)
75 100
29421 G08
LTC2942-1
Total Charge Error vs Temperature
1.00
TEMPERATURE
0.75 COMPENSATION
TRIM DEVIATION
0.50 +50ppm/K
OPTIMUM
0.25 –50ppm/K
0
–0.25
–0.50
–0.75
–1.00
–50
–25
0
|ISENSE| = 200mA
25 50 75 100
TEMPERATURE (°C)
24921 G03
Voltage Measurement ADC
Total Unadjusted Error
10
8
6
4 TA = 85°C
2
0
–2 TA = –45°C
–4
–6 TA = 25°C
–8
–10
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VSENSE– (V)
29421 G06
Sense Resistor Stability
0 ACCELERATED LOAD LIFE TEST
–0.5
DATA SCALED TO TAMB = 85°C,
ISENSE = 1A CONDITIONS
–1.0
–1.5
–2.0
–2.5
–3.0
0 10 20 30 40 50
kHOURS
29421 G09
29421f
5 Page 
LTC2942-1
Applications Information
Example: a register value
corresponds to a voltage
oofnI[S7E:0N]S=E–B0ohf:and
J[7:0]
=
1Ch
VSENSE–
=
6V
•
B01Ch
FFFFh
=
6V
•
45084DEC
65535
≈
4.1276V
Voltage is measured at the internal bond pads connected to
SENSE–, hence, the current flowing through the combined
pin and bond wire resistance causes the measured voltage
to deviate slightly from the actual battery voltage at the
SENSE– package pin. For the full-scale current of ±1A at
room temperature, this error is typically ±9mV, which is
negligible in most applications. To increase the precision
of the voltage measurement, the error can be reduced by
differentiating the coulomb counter data, multiplying the
resultant current value by 9 mΩ, and adding or subtract-
ing the result from the voltage measurement. Note that
the sign of the error changes depending on the direction
of the current flow.
The actual temperature can be obtained from the two byte
register C[7:0]D[7:0] by:
T
=
600K
•
RESULTh
FFFFh
=
600K
•
RESULTDEC
65535
Example: a register value of C[7:0] = 80h D[7:0] = 00h
corresponds to 300K or 27°C.
Temperature is measured on the surface of the chip (TDIE),
which may be different from ambient temperature TAMB,
especially with high sense resistor currents. To minimize
errors in the temperature measurement, the DFN package’s
exposed pad may be thermally coupled to the body whose
temperature is to be measured. With the recommended PCB
layout (Figure 11), TDIE typically increases over TAMB by
1K for 0.25A, 3K for 0.5A and 12K for 1A. Different results
may be obtained depending on layout, mounting details,
and air flow. Software in the host system can reduce this
error if the rise over TAMB is known by differentiating the
coulomb counter data to obtain current and using this
value to correct the temperature reading.
Threshold Registers (E, F, G, H, K, L, O, P)
For each of the measured quantities (battery charge, volt-
age and temperature) the LTC2942-1 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 LTC2942‑1
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 LTC2942-1 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 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 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 ad-
dressed is considered a slave. The LTC2942-1 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 com-
municating with the slave, it issues a STOP condition by
29421f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC2942-1.PDF ] | |
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