Datasheet

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LTC2942-1

29421f

Typical applicaTion

DescripTion

1A Battery Gas Gauge with

Internal Sense Resistor and

Temperature/Voltage

Measurement

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/I

C 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.

FeaTures

applicaTions

Indicates Accumulated Battery Charge and

Discharge

SMBus/I

C Interface

Integrated 50mΩ High Side Sense Resistor

±1A Sense Current Range

High Accuracy Analog Integration

ADC Measures Battery Voltage and Temperature

Integrated Temperature Sensor

1% Voltage and Charge Accuracy

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

Low Power Handheld Products

Cellular Phones

MP3 Players

Cameras

GPS

Total Charge Error vs Sense Current

SENSE

C/SMBus

TO HOST

SENSE

–

CHARGER

LTC2942-1

AL/CC

SDA

LOAD

0.1µF

29421 TA01a

1-CELL

Li-Ion

SCL

GND

SENSE

| (mA)

–0.50

CHARGE ERROR (%)

–0.25

–0.75

0.25

0.50

10 100 1000

29421 TA01b

–1.00

SENSE

+ = 3.6V

1.00

0.75

Summary of content (16 pages)

PAGE 1
LTC2942-1 1A Battery Gas Gauge with Internal Sense Resistor and Temperature/Voltage Measurement Description Features n n n n n n n n n n n n Indicates Accumulated Battery Charge and Discharge SMBus/I2C Interface Integrated 50mΩ High Side Sense Resistor ±1A Sense Current Range High Accuracy Analog Integration ADC Measures Battery Voltage and Temperature Integrated Temperature Sensor 1% Voltage and Charge Accuracy Configurable Alert Output/Charge Complete Input 2.7V to 5.
PAGE 2
LTC2942-1 Absolute Maximum Ratings (Notes 1, 2) Pin Configuration Supply Voltage (SENSE+).............................. –0.3V to 6V SCL, SDA, AL/CC.......................................... –0.3V to 6V Sense Current (into SENSE–).....................................±2A Operating Ambient Temperature Range LTC2942-1C.............................................. 0°C to 70°C LTC2942-1I........................................... –40°C to 85°C Storage Temperature Range....................
PAGE 3
LTC2942-1 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 ∆VLSB 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.
PAGE 4
LTC2942-1 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 tof Data Output Fall Time l 20 + 0.
PAGE 5
LTC2942-1 Typical Performance Characteristics Total Charge Error vs Sense Current Total Charge Error vs Supply Voltage 1.00 –0.25 –0.50 CHARGE ERROR (%) 0 0.4 0.2 0 –0.2 –0.4 –0.6 –0.75 VSENSE+ = 2.7V VSENSE+ = 4.2V 1 10 100 |ISENSE| (mA) –1.0 1000 2.5 3 3.5 4.5 4 VSENSE+ (V) 5 29421 G01 60 3.5 4.0 4.5 5.0 VSENSE + (V) 5.5 1.0 0 6.0 TA = 25°C TA = –40°C TA = 85°C 2.5 3.0 3.5 4.0 4.5 5.0 VSENSE + (V) 5.5 29421 G04 TA = 25°C –0.5 –1.0 2.5 3.0 3.5 4.0 4.5 5.
PAGE 6
LTC2942-1 Pin Functions SENSE+ (Pin 1): Positive Current Sense Input and Power Supply. Connect to the load and battery charger output. VSENSE+ operating range is 2.7V to 5.5V. GND (Pin 2): Device Ground. Connect directly to the negative battery terminal. 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].
PAGE 7
LTC2942-1 Operation Coulomb Counter Charge is the time integral of current. The LTC2942-1 measures battery current by monitoring the voltage developed across its internal sense resistor and then integrates this information to infer charge. The internal sense resistor is tied between the SENSE+ and SENSE– pins and is connected to an auto-zeroed differential analog integrator which converts the measured current to charge.
PAGE 8
LTC2942-1 Applications Information I2C/SMBus Interface Status Register (A) The LTC2942-1 communicates with a bus master using a 2-wire interface compatible with I2C and SMBus. The 7-bit hard-coded I2C address of the LTC2942-1 is 1100100. The status of the charge, voltage and temperature alerts is reported in the status register shown in Table 2. The LTC2942-1 is a slave-only device. Therefore the serial clock line (SCL) is an input only while the serial data line (SDA) is bidirectional.
PAGE 9
LTC2942-1 Applications Information The hard-coded bit A[7] of the status register enables the host to distinguish the LTC2942-1 from the pin compatible LTC2941, allowing the same software to be used with both devices. Control Register (B) The operation of the LTC2942-1 is controlled by programming the control register. Table 3 shows the organization of the 8-bit control register B[7:0]. Table 3.
PAGE 10
LTC2942-1 Applications Information Note that the internal digital resolution of the coulomb counter is higher than indicated by qLSB. The internal charge resolution is typically 299µAs. ADC Mode B[7:6] The LTC2942-1 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.
PAGE 11
LTC2942-1 Applications Information 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 • ≈ 4.1276 V FFFFh 65535 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.
PAGE 12
LTC2942-1 Applications Information 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). Data Transmission After a START condition, the I2C bus is considered busy and data transfer begins between a master and a slave.
PAGE 13
LTC2942-1 Applications Information 1000h at 1A current and 85°C ambient temperature; this outperforms most types of discrete sense resistors except those of the very high and ultrahigh stability variety. See the Typical Performance Characteristics for expected resistor drift performance under worst-case conditions. Drift will be much slower at lower temperatures. Contact LTC applications for more information. sense resistor drift over product lifetime or calibration intervals is less than –2%.
PAGE 14
LTC2942-1 Applications Information S ALERT RESPONSE ADDRESS R A DEVICE ADDRESS A 0001100 1 0 11001001 1 P 29421 F08 Figure 8. LTC2942-1 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 29421 F09 Figure 9.
PAGE 15
LTC2942-1 Applications Information Measuring Current In some applications, it may be desirable to measure the current ISENSE flowing through the internal sense resistor. Since charge measured by the coulomb counter is the time integral over ISENSE, differentiation of the contents of the accumulated charge register (ACR) over time may be used to measure average current.
PAGE 16
LTC2942-1 Typical Application Single Cell Lithium-Ion Coulomb Counter with Battery Charger for Discharge Currents of up to 1A 4 VIN 5V VCC BAT 3 3.3V LTC4057-4.2 (CHARGER) 1µF 5 2k PROG SHDN GND LOAD 0.1µF 2k 1 VDD µP 2 2k 2k 1 SENSE+ LTC2942-1 5 AL/CC 4 6 SDA SENSE– 3 + SCL GND 1-CELL Li-Ion 2 29421 TA02 Related Parts PART NUMBER DESCRIPTION COMMENTS Battery Gas Gauges LTC2942 Battery Gas Gauge with I2C Interface and Voltage and Temperature ADC 2.7V to 5.