Rainbow Electronics MAX17047 User Manual

19-6008; Rev 0; 9/11

MAX17047

ModelGauge m3 Fuel Gauge

General Description

The MAX17047 incorporates the Maxim ModelGauge™ m3 algorithm that combines the excellent short-term accuracy and linearity of a coulomb counter with the excellent long-term stability of a voltage-based fuel gauge, along with temperature compensation to provide industryleading fuel-gauge accuracy. ModelGauge m3 cancels offset accumulation error in the coulomb counter, while providing better short-term accuracy than any purely voltage-based fuel gauge. Additionally, the ModelGauge m3 algorithm does not suffer from abrupt corrections that normally occur in coulomb-counter algorithms, since tiny continual corrections are distributed over time.

The device automatically compensates for aging, temperature, and discharge rate and provides accurate state of charge (SOC) in mAh or % over a wide range of operating conditions. The device provides two methods for reporting the age of the battery: reduction in capacity and cycle odometer.

The device provides precision measurements of current, voltage, and temperature. Temperature of the battery pack is measured using an external thermistor supported by ratiometric measurements on an auxiliary input. A 2-wire (I2C) interface provides access to data and control registers. The IC is available in a lead(Pb)-free, 3mm x 3mm, 10-pin TDFN package.

Applications

2.5G/3G/4G Wireless Handsets

Smartphones/PDAs

Tablets and Handheld Computers

Portable Game Players

e-Readers

Digital Still and Video Cameras

Portable Medical Equipment

Features

S Accurate Battery-Capacity Estimation

 Temperature, Age, and Rate Compensated  Does Not Require Empty, Full, or Idle States to

Maintain Accuracy

S Precision Measurement System

 No Calibration Required

S ModelGauge m3 Algorithm

 Long-Term Influence by Voltage Fuel Gauge

Cancels Coulomb-Counter Drift

 Short-Term Influence by Coulomb Counter

Provides Excellent Linearity  Adapts to Cell Characteristics

S External Temperature-Measurement Network

Actively Switched Thermistor Resistive Divider  Reduces Current Consumption

S Low Quiescent Current

 25µA Active, < 0.5µA Shutdown

S Alert Indicator for SOC, Voltage, Temperature, and

Battery Removal/Insertion Events

S AtRate Estimation of Remaining Capacity

S 2-Wire (I2C) Interface

S Tiny, Lead(Pb)-Free, 3mm x 3mm, 10-Pin TDFN

Package

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part, refer to: www.maxim-ic.com/MAX17047.related

Simplified Operating Circuit

BATTERY PACK

PK+

OPTIONAL 10kI

T

PROTECTION

ModelGauge is a trademark of Maxim Integrated Products, Inc.

�� Maxim Integrated Products 1

OPTIONAL 10kI NTC THERMISTOR

PK-

OPTIONAL 10nF

V

BATTVTT

THRM

AIN SCL

REG

0.1µF0.1µF

MAX17047

CSP

10mI

RSNS

SYSTEM

ALRT

SDA

CSNEP

HOST

µP

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

MAX17047

ModelGauge m3 Fuel Gauge

ABSOLUTE MAXIMUM RATINGS

V

, SDA, SCL, ALRT to CSP .............................-0.3V to +6V

BATT

REG to CSP ..........................................................-0.3V to +2.2V

VTT to CSP ............................................................... -0.3V to +6V

THRM, AIN to CSP .....................................-0.3V to (VTT + 0.3V)

CSN to CSP ................................................................-2V to +2V

Continuous Sink Current (VTT) ...........................................20mA

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(V

= 2.5V to 4.5V, TA = -20NC to +70NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)

BATT

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage V

Supply Current

REG Regulation Voltage V

Measurement Error, V

Measurement Resolution, V V

Measurement Range V

BATT

I

DD0

I

DD1

V

GERR

V

REG

LSb

FS

Input Resistance CSN, AIN 15

Ratiometric Measurement Accuracy, AIN

Ratiometric Measurement Resolution, AIN

Current Register Resolution I Current Full-Scale Magnitude I Current Offset Error I

Current Gain Error I

Time-Base Accuracy t

T

GERR

T

LSb

OERR

GERR

ERR

LSb

FS

THRM Output Drive I THRM Precharge Time t

SDA, SCL, ALRT Input Logic High

PRE

V

IH

SDA, SCL, ALRT Input Logic Low V SDA, ALRT Output Logic Low V SDA, ALRT Pulldown Current I

OL

PD

ALRT Leakage 1 THRM Operating Range 2.5 V

(Note 2) 2.5 4.5 V Shutdown mode, TA P +50NC Active mode, average current 25 42

TA = +25NC

V

= 3.6V at TA = +25NC

DD

TA = 0NC to +50NC TA = -20NC to +70NC

= 0.5mA V

OUT

0.5 V

IL

IOL = 4mA 0.4 V Active mode, V

Continuous Sink Current (SCL, SDA, ALRT) ......................20mA

Operating Temperature Range .......................... -40NC to +85NC

Storage Temperature Range ............................ -55NC to +125NC

Lead Temperature (soldering 10s) .................................+300NC

Soldering Temperature (reflow) ......................................+260NC

0.5 2

1.5 1.9 V

-7.5 +7.5

-20 +20

0.625 mV

2.5 4.98 V

-0.5 +0.5 %

0.0244

1.5625

Q51.2

Q1.5 FV

-1 +1

-2.5 +2.5

-3.5 +3.5

- 0.1 V

TT

8.48 ms

1.5 V

SDA

= 0.4V, V

= 0.4V 0.05 0.2 0.4

ALRT

TT

FA

mV

MI

% Full

Scale

FV

mV

% of

Reading

%

FA FA

V

�� Maxim Integrated Products 2

MAX17047

ModelGauge m3 Fuel Gauge

ELECTRICAL CHARACTERISTICS (continued)

(V

= 2.5V to 4.5V, TA = -20NC to +70NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)

BATT

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Battery-Removal Detection Threshold—V

AIN

Rising

Battery-Removal Detection Threshold—V

AIN

Falling

Battery-Removal Detection Comparator Delay

External AIN Capacitance

ELECTRICAL CHARACTERISTICS (2-WIRE INTERFACE)

(2.5V P V

SCL Clock Frequency f

Bus Free Time Between a STOP and START Condition

Hold Time (Repeated) START Condition

Low Period of SCL Clock t High Period of SCL Clock t

Setup Time for a Repeated START Condition

Data Hold Time t Data Setup Time t

Rise Time of Both SDA and SCL Signals

Fall Time of Both SDA and SCL Signals

Setup Time for STOP Condition t

Spike Pulse Widths Suppressed by Input Filter

Capacitive Load for Each Bus Line

SCL, SDA Input Capacitance C

Note 1: Specifications are 100% tested at TA = +25°C. Limits over the operating range are guaranteed by design and

Note 2: All voltages are referenced to CSP. Note 3: Timing must be fast enough to prevent the device from entering shutdown mode due to bus low for a period > 45s minimum. Note 4: f Note 5: The maximum t Note 6: This device internally provides a hold time of at least 100ns for the SDA signal (referred to the minimum VIH of the SCL

Note 7: Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant. Note 8: CB—total capacitance of one bus line in pF.

P 4.5V, TA = -20NC to +70NC.) (Note 1)

BATT

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

characterization.

must meet the minimum clock low time plus the rise/fall times.

SCL

HD:DAT

signal) to bridge the undefined region of the falling edge of SCL.

V

DETR

V

t

TOFF

DETF

V

- V

THRM

V

THRM

V

AIN

- V

AIN

step from 70% to 100% of V

ALRT falling; Alrtp = logic 0;

THRM

to

EnAIN = logic 1; FTHRM = logic 1

R

= 10kI NTC

THM

SCL

t

BUF

t

HD:STA

LOW

HIGH

t

SU:STA

HD:DAT

SU:DAT

t

R

t

SU:STO

t

SP

C

BIN

(Note 3) 0 400 kHz

(Note 4) 0.6

(Notes 5, 6) 0 0.9 (Note 5) 100 ns

F

(Note 7) 0 50 ns

(Note 8) 400 pF

B

has only to be met if the device does not stretch the low period (t

40 125 200 mV

70 150 230 mV

100

100 nF

1.3

0.6

20 +

0.1C

20 +

0.1C

B

300 ns

0.6

60 pF

) of the SCL signal.

LOW

Fs

Fs Fs

Fs

�� Maxim Integrated Products 3

SDA

SCL

MAX17047

ModelGauge m3 Fuel Gauge

I2C Bus Timing Diagram

t

F

t

LOW

t

R

SU:DAT

t

F

t

HD:STA

t

SPtR

t

BUF

t

HD:STA

S Sr

Figure 1. I2C Bus Timing Diagram

(T

= +25°C, unless otherwise noted.)

A

SHUTDOWN CURRENT vs. SUPPLY VOLTAGE

0.8

0.7

0.6

0.5

0.4

0.3

SHUTDOWN CURRENT (µA)

0.2

0.1

0

T

= +25°C

A

T

= +70°C

A

TA = -20°C

V

(V)

BATT

t

HD:DAT

t

SU:STA

t

SU:STO

P

S

Typical Operating Characteristics

ACTIVE CURRENT vs. SUPPLY VOLTAGE

35

30

MAX17047 toc01

25

20

15

ACTIVE CURRENT (µA)

10

5

541 2 3

0

= +25°C

T

A

T

= +70°C

A

MAX17047 toc02

TA = -20°C

54321

V

(V)

BATT

vs. TEMPERATURE AND SUPPLY VOLTAGE

10

8

6

4

2

0

-2

-4

VOLTAGE ADC ERROR (mV)

-6

-8

-10

2.2

VOLTAGE ADC ERROR

TA = -20°C

V

BATT

(V)

T

A

T

A

= +70°C

= +25°C

MAX17047 toc03

4.23.73.22.7

�� Maxim Integrated Products 4

(T

= +25°C, unless otherwise noted.)

A

MAX17047

ModelGauge m3 Fuel Gauge

Typical Operating Characteristics (continued)

CURRENT ADC ERROR

vs. TEMPERATURE

15

10

5

0

-5

CURRENT ADC ERROR (mA)

TA = +25°C

-10

-15

-2 2

TA = -20°C

CURRENT FORCED (A)

RESPONSE TO TEMPERATURE TRANSIENT

AT CONSTANT-CURRENT LOAD

100

90

80

70

60

50

40

30

FUEL GAUGE CHANGES

SOC (%), TEMPERATURE (°C)

TRAJECTORY AFTER

20

TEMPERATURE CHANGE

10

0

TEMPERATURE

0 3

V

RISES WITH

CELL

TEMPERATURE DURING

CONSTANT LOAD

EMPTY VOLTAGE

21

TIME (Hr)

TA = +70°C

10-1

MAX17047 toc06

SOC

AV

SOC

REP

MAX17047 toc04

4.4

4.2

4.0

3.8

3.6

3.4

3.2

3.0

2.8

2.6

2.4

(V)

CELL

V

AUXILIARY INPUT ADC ERROR

vs. TEMPERATURE

1.00

0.80

0.60

0.40

0.20

0

-0.20

-0.40

-0.60

AUXILIARY INPUT ADC ERROR (%)

-0.80

-1.00

AIN RATIO TO VTT (%)

TA = -20°C

T

END-OF-CHARGE DETECTION

8000

FullCAP

7000

6000

V

5000

4000

3000

2000

1000

CAPACITY (mAh); CURRENT (mA)

-1000

-2000

CELL

0

0 8

VALID END-OF-CHARGE

DETECTION EVENT

RemCap

REP

TIME (Hr)

TA = +70°C

= +25°C

A

MAX17047 toc07

NEAR-FULL

FALSE CHARGE

TERMINATION

EVENTS

CURRENT

642

908060 7020 30 40 50100 100

MAX17047 toc05

4.7

4.5

4.3

4.1

3.9

3.7

3.5

3.3

3.1

2.9

2.7

(V)

CELL

V

�� Maxim Integrated Products 5

(TA = +25°C, unless otherwise noted.)

MAX17047

ModelGauge m3 Fuel Gauge

Typical Operating Characteristics (continued)

100

90

80

70

60

50

40

30

20

10

STATE OF CHARGE (%) OR TEMPERATURE (°C)

0

SOC

0 10

REFERENCE SOC

ERROR

REP

TIME (Hr)

CHARGE AND DISCHARGE AT +20°C

100

90

COLD DISCHARGE (0°C)

80

70

60

50

40

STATE OF CHARGE (%)

30

20

10

0

0 15

SOC

REFERENCE SOC

C/4 DISCHARGE C/7 DISCHARGE

C/9 DISCHARGE

REP

C/2 DISCHARGE

ERROR

105

TIME (Hr)

MAX17047 toc08

8642

MAX17047 toc10

10

8

6

4

2

0

-2

-4

-6

-8

-10

10

8

6

4

2

0

-2

-4

-6

-8

-10

ERROR (%)

100

90

80

70

60

50

40

STATE OF CHARGE (%)

30

20

10

0

0 10

SOC

C/4 DISCHARGE

ERROR

REP

TIME (Hr)

CHARGE AND DISCHARGE IN

ACTUAL SYSTEM

100

90

80

DISCHARGE AT +40°C

70

60

50

40

30

20

10

STATE OF CHARGE (%) OR TEMPERATURE (°C)

0

V

CELL

TEMPERATURE

SOC

REFERENCE SOC

TIME (Hr)

REP

(%)

MAX17047 toc09

REFERENCE SOC

8642

MAX17047 toc11

(%)

105

10

8

6

4

2

0

-2

-4

-6

-8

-10

4.2

4.1

4.0

3.9

3.8

3.7

3.6

3.5

3.4

3.3

3.2

ERROR (%)

(V)

CELL

V

�� Maxim Integrated Products 6

TOP VIEW

MAX17047

ModelGauge m3 Fuel Gauge

Pin Configuration

V

SCL

SDA

+

1

TT

2 9

3

4

5 6

MAX17047

TDFN

V

10

BATT

THRMAIN

ALRT

8

REG

7

EP

CSPCSN

PIN NAME FUNCTION

1 V

2 AIN

Supply Input for Thermistor Bias Switch. Connect to supply for ratiometric AIN pin-voltage measurements.

TT

In most applications, connect VTT to V

BATT

.

Auxiliary Voltage Input. Auxiliary voltage input from external thermal-measurement network. AIN also provides battery insertion/removal detection. Connect to V

, if not used.

BATT

3 SCL Serial Clock Input. 2-wire clock line. Input only. 4 SDA Serial Data Input/Out. 2-wire data line. Open-drain output driver. 5 CSN Sense Resistor Connection. System ground connection and sense resistor input. 6 CSP Chip Ground and Sense Resistor Input 7 REG

Voltage Regulator Bypass. Connect a 0.1FF capacitor from REG to CSP.

Alert Indication. An open-drain n-channel output used to indicate specified condition thresholds have been

8 ALRT

met. A 200kI pullup resistor to power rail is required for use as an output. Alternatively, ALRT can operate as a shutdown input with the output function disabled.

9 THRM

10 V

BATT

Thermistor Bias Connection. Supply for thermistor resistor-divider. Connect to the high side of the thermistor/resistor-divider. THRM connects internally to VTT during temperature measurement.

Power-Supply and Battery Voltage-Sense Input. Kelvin connect to positive terminal of battery pack. Bypass with a 0.1FF capacitor to CSP.

— EP Exposed Pad. Connect to CSP.

Pin Description

�� Maxim Integrated Products 7

0.1µF

PK-

PK+

0.1µF

10nF

PK+

PK-

V

BATT

REG

V

TT

THRM

V

THRM

- V

DETR/VDETF

AIN

MAX17047

ModelGauge m3 Fuel Gauge

Block Diagram

IN

2V LDO

OUT

P

PK- SYSTEM GROUND

32kHz OSCILLATOR

OCV CALCULATION

MAX17047

BATTERY REMOVAL

DETECT

CSP CSN

10mI

RSNS

V

BATT

MUX

REF ADC

12-BIT ADC

ModelGauge m3

ALGORITHM

REF

2

I

C

INTERFACE

ALRT

CSP

SDA

SCL

Detailed Description

The MAX17047 incorporates the Maxim ModelGauge m3 algorithm that combines the excellent short-term accuracy and linearity of a coulomb counter with the excellent long-term stability of a voltage-based fuel gauge, along with temperature compensation to provide industryleading fuel-gauge accuracy. ModelGauge m3 cancels offset accumulation error in the coulomb counter, while providing better short-term accuracy than any purely voltage-based fuel gauge. Additionally, the ModelGauge m3 algorithm does not suffer from abrupt corrections that normally occur in coulomb-counter algorithms, since tiny continual corrections are distributed over time.

The device automatically compensates for aging, temperature, and discharge rate and provides accurate SOC in mAh or % over a wide range of operating conditions. The device provides two methods for reporting the age of the battery: reduction in capacity and cycle odometer.

The device provides precision measurements of current, voltage, and temperature. Temperature of the battery pack is measured using an external thermistor supported

�� Maxim Integrated Products 8

by ratiometric measurements on an auxiliary input. A 2-wire (I2C) interface provides access to data and control registers. The device is available in a 3mm x 3mm, 10-pin TDFN package.

ModelGauge m3 Algorithm

The ModelGauge m3 algorithm combines a high-accuracy coulomb counter with a voltage fuel gauge (VFG) as represented in Figure 2.

Classical coulomb-counter-based fuel gauges have excellent linearity and short-term performance. However, they suffer from drift due to the accumulation of the offset error in the current-sense measurement. Although the offset error is often very small, it cannot be eliminated, causes the reported capacity error to increase over time, and requires periodic corrections. Corrections are usually performed at full or empty. Some other systems also use the relaxed battery voltage to perform corrections. These systems determine the SOC based on the battery voltage after a long time of no current flow. Both have the same limitation: if the correction condition is not observed over time in the actual application, the error in

RELAXED

CELL

DETECTION

VOLTAGE

OCV TEMPERATURE-

COMPENSATION LEARN

CAPACITY LEARN

mAh PER %

ModelGauge m3 Fuel Gauge

VOLTAGE FUEL GUAGE

OCV CALCULATION

OCV OUTPUT

EMPTY

DETECTION

OCV TABLE LOOKUP

% REMAINING OUTPUT

MIXING ALGORITHM

mAh OUTPUT

RemCap

MIX

SOC

MIX

MAX17047

COULOMB COUNTER

mAh OUTPUT

CURRENT

TIME

CURRENT

TEMPERATURE

APPLICATION

EMPTY

COMPENSATION

END-OF-CHARGE

DETECTION

Figure 2. ModelGauge m3 Overview

the system is boundless. The performance of classic coulomb counters is dominated by the accuracy of such corrections.

Classical voltage-measurement-based SOC estimation has poor accuracy due to inadequate cell modeling, but does not accumulate offset error over time.

The device includes an advanced VFG, which estimates open-circuit voltage (OCV), even during current flow, and simulates the nonlinear internal dynamics of a lithium-ion (Li+) battery to determine the SOC with improved accuracy. The model considers the time effects of a battery caused by the chemical reactions and impedance in the battery to determine SOC based on table lookup. This SOC estimation does not accumulate offset error over time.

The ModelGauge m3 algorithm combines a high-accuracy coulomb counter with a VFG. The complementary

APPLICATION

OUTPUTS:

SOC

REP

RemCap

REP

SOC

AV

RemCap

AV

TTE FullCAP

CELL CHEMISTRY

OUTPUTS:

OCV CYCLES R

CELL

FullCAPNom AGE

combined result eliminates the weaknesses of both the coulomb counter and the VFG, while providing the strengths of both. A mixing algorithm combines the VFG capacity with the coulomb counter and weighs each result so that both are used optimally to determine the battery state. In this way, the VFG capacity result is used to continuously make small adjustments to the battery state, canceling the coulomb-counter drift.

The ModelGauge m3 algorithm uses this battery state information and accounts for temperature, battery current, age, and application parameters to determine the remaining capacity available to the system.

The ModelGauge m3 algorithm continually adapts to the cell and application through independent learning routines. As the cell ages, its change in capacity is monitored and updated and the VFG dynamics adapt based on cellvoltage behavior in the application.

�� Maxim Integrated Products 9

MAX17047

ModelGauge m3 Fuel Gauge

OCV Estimation and Coulomb-Count Mixing

The core of the ModelGauge m3 algorithm is a mixing algorithm that combines the OCV state estimation with the coulomb counter. After power-on reset of the IC, coulomb-count accuracy is unknown. The OCV state estimation is weighted heavily compared to the coulombcount output. As the cell progresses through cycles in the application, coulomb-counter accuracy improves and the mixing algorithm alters the weighting so that the coulomb-counter result is dominant. From this point forward, the IC switches to servo mixing. Servo mixing provides a fixed magnitude error correction to the coulomb count, up or down, based on the direction of error from the OCV estimation. This allows differences between the coulomb count and OCV estimation to be corrected quickly. See Figure 3.

100%

COULOMB-COUNT INFLUENCE SERVO MIXING

MIXING RATIO

OCV AND COULOMB-COUNT

OCV

INFLUENCE

0%

CELL CYCLES

Figure 3. ModelGauge m3 OCV and Coulomb-Count Mixing

1.501.000.500

2.00

The resulting output from the mixing algorithm does not suffer drift from current measurement offset error and is more stable than a stand-alone OCV estimation algorithm; see Figure 4. Initial accuracy depends on the relaxation state of the cell. The highest initial accuracy is achieved with a fully relaxed cell.

Fuel-Gauge Empty Compensation

As the temperature and discharge rate of an application changes, the amount of charge available to the applica tion also changes. The ModelGauge m3 algorithm dis tinguishes between remaining capacity of the cell (RemCap

) and remaining capacity of the appli-

MIX

cation (RemCapAV) and reports both results to the user.

Fuel-Gauge Learning

The device periodically makes internal adjustments to cell characterization and application information to remove initial error and maintain accuracy as the cell ages. These adjustments always occur as small undercorrections to prevent instability of the system and prevent any noticeable jumps in the fuel-gauge outputs. Learning occurs automatically without any input from the host. To maintain learned accuracy through power loss, the host must periodically save learned information and then restore after power is returned. See the Power-Up

and Power-On Reset section for details:

• Application Capacity (FullCAP). This is the total capacity available to the application at full. Through the user-defined registers, ICHGTerm and FullSOCThr, the device detects end-of-charge conditions as the cell is cycled. These points allow the device to learn the capacity of the cell based on the charge termination experienced during operation.

TYPICAL OCV ESTIMATION

ERROR AS CELL IS CYCLED

STATE-OF-CHARGE ERROR

TIME

Figure 4. ModelGauge m3 Algorithm Mixing Conceptual Illustration

�� Maxim Integrated Products 10

MAXIMUM COULOMB-COUNTER ERROR

(SHADED AREA) ModelGauge m3

OCV + COULOMB-COUNT MIXING

MAXIMUM ERROR RANGE

MAX17047

ModelGauge m3 Fuel Gauge

• Cell Capacity (FullCapNom). This is the total cell capacity at full, according to the VFG. This includes some capacity that is not available to the application at high loads and/or low temperature. The device periodically compares percent change based on OCV measurement vs. coulomb-count change as the cell charges and discharges. This information allows the device to maintain an accurate estimation of the cell’s capacity in mAh as the cell ages.

• Voltage Fuel-Gauge Adaptation. The device observes the battery’s relaxation response and adjusts the dynamics of the VFG. This adaptation adjusts the RCOMP0 register during qualified cell relaxation events.

• Empty Compensation. The device updates inter- nal data whenever cell empty is detected (V V�empty) to account for cell age or other cell deviations from the characterization information.

CELL

<

Determining Fuel-Gauge Accuracy

To determine the true accuracy of a fuel gauge, as experienced by end users, the battery should be exercised in a dynamic manner. The end-user accuracy cannot be understood with only simple cycles.

To challenge a correction-based fuel gauge, such as coulomb counters, test the battery with partial loading sessions. For example, a typical user may operate the device for 10min and then stop using for an hour or more. A robust test method includes these kinds of sessions many times at various loads, temperatures, and duration. Refer to Application Note 4799: Cell Characterization Procedure for a ModelGauge m3 Fuel Gauge.

Initial Accuracy

The device uses the first voltage reading after power-up or after cell insertion to determine the starting output of the fuel gauge. It is assumed that the cell is fully relaxed prior to this reading; however, this is not always the case. If the cell was recently charged or discharged, the voltage measured by the device may not represent the

true state of charge of the cell, resulting in initial error in the fuel gauge outputs. In most cases, this error is minor and is quickly removed by the fuel gauge algorithm during normal operation.

Typical Operating Circuit

The device is designed to mount outside the cell pack that it monitors. Voltage of the battery pack is measured directly at the pack terminals by the V connections. Current is measured by an external sense resistor placed between the CSP and CSN pins. An external resistor-divider network allows the device to measure temperature of the cell pack by monitoring the AIN pin. The THRM pin provides a strong pullup for the resistor-divider that is internally disabled when temperature is not being measured.

Communication to the host occurs over a standard I2C interface. SCL is an input from the host, and SDA is an open-drain I/O pin that requires an external pullup. The ALRT pin is an output that can be used as an external interrupt to the host processor if certain application conditions are detected. ALRT can also function as an input, allowing the host to shut down the device. This pin is also open drain and requires an external pullup resistor.

Figure 5 is the typical operating circuit.

The device can share the cell thermistor circuit with the system charger. In this circuit, there is a single thermistor inside the cell pack and a single bias resistor external to the cell pack. The device shares the same external bias as the charger circuit and measurement point on the thermistor. In this configuration, each device can measure temperature individually or simultaneously without interference. Alternatively, if the bias voltage in the charger circuit is not available to the device, a separate bias voltage on the VTT pin can be used. For proper operation, the separate bias voltage must be larger than the minimum operating voltage of the device, but no larger than one diode drop above the charger circuit bias voltage. See Figure 6.

BATT

and CSP

�� Maxim Integrated Products 11

MAX17047

ModelGauge m3 Fuel Gauge

BATTERY PACK

THERMISTOR

MEASUREMENT OPTIONAL

OPTIONAL

PROTECTION IC

THERMISTOR

Figure 5. Typical Operating Circuit

10kI

NTC

PK+

T

PK-

OPTIONAL 10nF

V

BATTVTT

THRM

OPTIONAL 10kI

REG

0.1µF0.1µF

MAX17047

AIN SCL

CSP

10mI

RSNS

BIAS

V

< V

2.8V < V

BIAS

INTERNAL

SYSTEM

OPTIONAL

ALRT

SDA

CSNEP

+ 0.6V

200kI

OPTIONAL

5kI

HOST

µP

CHARGER WITH

V

+ THRM

TT

AVAILABLE

THERMISTOR

CELL PACK

V

BIAS

VOLTAGE BASED

P P

ON EXISTING

CHARGER REQUIREMENTS

INSIDE

V

THRM

AIN

MAX17047 + CHARGER

PK- PK-

MAX17047

TT

CSP

WITH EXTERNAL BIAS

V

SYSTEM

V

BATT

CHARGER WITH

INTERNAL

OFF DURING

DISCHARGE

THERMISTOR

CELL PACK

Figure 6. Operating Circuits that Share Pack Thermistor with System Charger

�� Maxim Integrated Products 12

BIAS

V

INTERNAL

ON DURING

CHARGE

INSIDE

MAX17047

V

TT

P

THRM

AIN

CSP

MAX17047 + CHARGER

WITH INTERNAL BIAS

V

SYSTEM

V

BATT

MAX17047

ModelGauge m3 Fuel Gauge

Recommended Layout

Proper circuit layout (see Figure 7) is essential for measurement accuracy when using the MAX17047 ModelGauge m3 IC. The recommended layout guidelines are as follows:

1) Mount R device shares both voltage and current measurements on the CSP pin. Therefore, it is important to limit the amount of trace resistance between the currentsensing resistor and PACK-.

2) V

BATT

PACK+. The device shares the V voltage measurement and IC power. Limiting the voltage loss through this trace is important to voltagemeasurement accuracy. PCB resistance that cannot be removed can be compensated for during characterization of the application cell.

POSITIVE POWER BUS

as close as possible to PACK-. The

SNS

trace should make a Kelvin connection to

pin for both

BATT

3) CSN and CSP traces should make Kelvin connections to R

. The device measures current differentially

SNS

through the CSN and CSP pins. Any shared highcurrent paths on these traces will affect currentmeasurement gain accuracy. PCB resistance that cannot be removed can be compensated for during characterization of the application cell.

4) V

capacitor trace loop area should be minimized.

BATT

The device shares the V

pin for both voltage mea-

BATT

surement and IC power. Limiting noise at the V

BATT

pin is important to current-measurement accuracy.

5) REG capacitor trace loop area should be minimized. The helps filter any noise from the internal regulated supply.

6) There are no limitations on any other IC connection. Connections to THRM, ALRT, SDA, SCL, VTT, and AIN, as well as any external components mounted to these pins, have no special layout requirements.

PACK + CONTACT

NEGATIVE POWER BUS

Figure 7. Proper Board Layout

�� Maxim Integrated Products 13

V

AIN

SCL

SDA

CSN

V

BATT

TT

THRM

MAX17047

EP

R

SNS

REG

ALRT

CSP

C

REG

C

VBATT

PACK CONTACT

MAX17047

ModelGauge m3 Fuel Gauge

ModelGauge m3 Registers

To calculate accurate results, ModelGauge m3 requires information about the cell, the application, and real-time information measured by the device. Figure 8 shows all inputs and outputs to the algorithm grouped by category. Analog input registers are the real-time measurements of voltage, temperature, and current performed by the device. Application-specific registers are programmed by the customer to reflect the operation of the applica-

V

CELL

CURRENT

ANALOG

INPUTS

APPLICATION

SPECIFIC

CELL

CHARACTERIZATION

INFORMATION

TEMPERATURE

AverageV

CELL

AverageCurrent

AverageTemperature

DesignCap

ICHGTerm

FullSOCThr

V_empty

CHARACTERIZATION

TABLE

QResidual Table

FCTC

RCOMP0

TempCo

TempNom

TempLim

V_empty

FullCapNom

Iavg_empty

LearnCFG

FilterCFG

RelaxCFG

MiscCFG

tion. The Cell Characterization Information registers hold characterization data that models the behavior of the cell over the operating range of the application. The Algorithm Configuration registers allow the host to adjust performance of the device for their application. The Save and Restore registers allow an application to maintain accuracy of the algorithm after the device has been power cycled. The following sections describe each register in detail.

SOC

MIX

RemCap

MIX

SOC

REP

RemCap

REP

SOC

AV

RemCap

AV

ModelGauge ALGORITHM OUTPUTS

SAVE AND RESTORE INFORMATION

ModelGauge ALGORITHM

ALGORITHM CONFIGURATION

AtRate

TTE

AGE

CYCLES

OCV

FullCAP

FullCapNom

FSTAT

FullCAP

CYCLES

QResidual Table

RCOMP0

TempCo

dQacc

dPacc

Figure 8. ModelGauge m3 Register Map

�� Maxim Integrated Products 14