Datasheet

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LTC2941-1

29411f

Typical applicaTion

DescripTion

1A I

C Battery Gas Gauge

with Internal Sense Resistor

The LTC

2941-1 measures battery charge state in battery-

powered 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. The measured

charge is stored in internal registers. An SMBus/I

C in-

terface accesses and conﬁgures the device.

The LTC2941-1 features programmable high and low

thresholds for accumulated charge. If a threshold is ex-

ceeded, the device communicates an alert using either the

SMBus alert protocol or by setting a ﬂag in the internal

status register.

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

1% 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 Player

Cameras

GPS

Total Charge Error vs Sense Current

SENSE

C/SMBus

TO HOST

SENSE

–

CHARGER

LTC2941-1

AL/CC

SDA

LOAD

0.1µF

29411 TA01a

1-CELL

Li-Ion

SCL

GND

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Hot

Swap, ThinSOT and Bat-Track are trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

SENSE

| (mA)

–0.50

CHARGE ERROR (%)

–0.25

–0.75

0.25

0.50

10 100 1000

29411 TA01b

–1.00

SENSE

+ = 3.6V

1.00

0.75

Summary of content (16 pages)

PAGE 1
LTC2941-1 1A I2C Battery Gas Gauge with Internal Sense Resistor Features n n n n n n n n n n Description Indicates Accumulated Battery Charge and Discharge SMBus/I2C Interface Integrated 50mΩ High Side Sense Resistor ±1A Sense Current Range High Accuracy Analog Integration 1% Charge Accuracy Configurable Alert Output/Charge Complete Input 2.7V to 5.
PAGE 2
LTC2941-1 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 LTC2941-1C.............................................. 0°C to 70°C LTC2941-1I........................................... –40°C to 85°C Storage Temperature Range......................
PAGE 3
LTC2941-1 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
PAGE 4
LTC2941-1 Typical Performance Characteristics Total Charge Error vs Supply Voltage Total Charge Error vs Sense Current 1.00 0 –0.25 –0.50 0.4 CHARGE ERROR (%) 0.25 0.2 0 –0.2 –0.4 –0.6 –0.75 VSENSE+ = 2.7V VSENSE+ = 4.2V 1 10 100 |ISENSE| (mA) 1000 2.5 3 3.5 4.5 4 VSENSE+ (V) 5 29411 G01 0 –0.25 –0.50 –1.00 –50 |ISENSE| = 200mA –25 0 50 25 TEMPERATURE (°C) 75 100 24911 G03 Shutdown Supply Current vs Supply Voltage Sense Resistor Stability 2.0 TA = 25°C TA = –40°C TA = 85°C 90 0.
PAGE 5
LTC2941-1 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 6
LTC2941-1 Block Diagram 1 6 2 VSUPPLY RBOND SENSE+ 12mΩ RBOND SENSE– 12mΩ RSENSE 50mΩ BIDIRECTIONAL INTEGRATOR REF PRESCALER M ACCUMULATED CHARGE REGISTER AL AL/CC 5 CLK I2C/ SMBus GND INTERNAL REFERENCE GENERATOR CC INTERNAL OSCILLATOR STATUS/ CONTROL REGISTER SCL SDA 3 4 29411 F02 Figure 2.
PAGE 7
LTC2941-1 Operation Overview The LTC2941-1 is a battery gas gauge device designed for use with single Li-Ion cells and other battery types with terminal voltages from 2.7V to 5.5V. A precision coulomb counter integrates current through an internal sense resistor between the battery’s positive terminal and the load or charger. The integrated, temperature-compensated sense resistor offers board space savings and superior charge measurement accuracy in applications with currents up to 1A.
PAGE 8
LTC2941-1 Applications Information I2C/SMBus Interface Status Register (A) The LTC2941-1 communicates with a bus master using a 2-wire interface compatible with I2C and SMBus. The 7-bit hard-coded I2C address of LTC2941-1 is 1100100. Table 2 shows the details of the status register (address 00h): The LTC2941-1 is a slave-only device. Therefore, the serial clock line (SCL) is input only while the data line (SDA) is bidirectional. The device supports I2C standard and fast mode.
PAGE 9
LTC2941-1 Applications Information Bit A[5] is set if the LTC2941-1’s accumulated charge overflows or underflows the combined total in registers C and D. Note that the counting process does not roll over, but simply stops at FFFFh or 0000h until the direction is reversed. The LTC2941-1 includes a battery undervoltage monitor, which sets bit A1 if the limit is exceeded. Limits are selected in the control register.
PAGE 10
LTC2941-1 Applications Information The default value after power up is M = 128 = 27 (B[5:3] = 111). The maximum battery capacity supported within the prescaler range is 5.5Ah with M = 128. See the section Extending Coulomb Counter Range if battery capacity is higher. Depending on the choice of prescaler factor M, the charge LSB of the accumulated charge register becomes: qLSB = 0.085mAh • M 128 Note that the internal digital resolution of the coulomb counter is higher than indicated by qLSB.
PAGE 11
LTC2941-1 Applications Information 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 LTC2941-1 always acts as a slave. Figure 4 shows an overview of the data transmission on the I2C bus.
PAGE 12
LTC2941-1 Applications Information SDA a6 - a0 b7 - b0 SCL 1-7 8 9 ADDRESS R/W ACK b7 - b0 1-7 8 9 1-7 8 9 S START CONDITION P DATA ACK DATA ACK STOP CONDITION 29411 F04 Figure 4. Data Transfer Over I2C or SMBus S ADDRESS W A REGISTER A DATA A 1100100 0 0 01h 0 FCh 0 P 29411 F05 FROM MASTER TO SLAVE A: ACKNOWLEDGE (LOW) A: NOT-ACKNOWLEDGE (HIGH) FROM SLAVE TO MASTER R: READ BIT (HIGH) W: WRITE BIT (LOW) S: START CONDITION P: STOP CONDITION Figure 5.
PAGE 13
LTC2941-1 Applications Information Internal Sense Resistor The internal sense resistor uses proprietary* temperature compensation techniques to reduce the effective temperature coefficient to less than ±50ppm/K typically. The effective sense resistance as seen by the coulomb counter is factory trimmed to 50mΩ.
PAGE 14
LTC2941-1 Applications Information where the factor 1.22 approximates the effect of sense resistor self-heating, RPP(MAX) is the maximum pad-topad resistance at nominal temperature (27°C) and θJA is the thermal resistance from junction to ambient.
PAGE 15
LTC2941-1 Package Description DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 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 R = 0.05 TYP 2.00 p0.10 (2 SIDES) 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.
PAGE 16
LTC2941-1 Typical Application Single Cell Lithium-Ion Coulomb Counter with Battery Charger for Discharge Currents of up to 1A 4 VIN 5V VCC BAT LTC4057-4.2 (CHARGER) 1µF 5 2k PROG SHDN GND 3 LOAD 0.1µF 3.