MAXIM DS2780 User Manual

Standalone Fuel Gauge IC

DS2780

www.maxim-ic.com

GENERAL DESCRIPTION

The DS2780 measures voltage, temperature and current, and estimates available capacity for rechargeable Lithium Ion and Lithium Ion Polymer batteries. Cell characteristics and application parameters used in the calculations are stored in onchip EEPROM. The available capacity registers report a conservative estimate of the amount of charge that can be removed given the current temperature, discharge rate, stored charge and application parameters. Capacity estimation reported in mAh remaining and percentage of full.

APPLICATIONS

Digital Still Cameras

Sub-Notebook Computers

Handheld PC Data Terminals

3G Multimedia Wireless Handsets

TYPICAL OPERATING CIRCUIT

PK+

DQ 5

PIO 8

NC 1

SNS 7

DS2780

3 VIN

6 OVD

2 VSS

TSSOP-8

RSNS

DATA

PK-

150

5.6V

500

VDD

0.1uF

1 Cell Li- Ion

Bat ter y

Protec tion

Cir c ui t

FEATURES

 Precision Voltage, Temperature, and Current

Measurement System

 Internal Time Base is Accurate and Temperature

Stable

 Absolute and Relative Capacity Estimated from

Coulomb Count, Discharge Rate, Temperature and Battery Cell Characteristics

 Accurate Warning of Low Battery Conditions  Automatic Backup of Coulomb Count and Age

Estimation to Nonvolatile (NV) EEPROM

 Gain and Tempco Calibration Allows the Use of

Low-Cost Sense Resistors

 24-Byte Battery/Application Parameter EEPROM  16-Byte User EEPROM  Unique ID and Multidrop 1-Wire

Interface

 Tiny 8-pin TSSOP & 10-pin TDFN Package

Embeds Easily in Battery Packs Using Thin Prismatic Cells

PIN CONFIGURATION

ORDERING INFORMATION

PART MARKING PACKAGE INFORMATION

DS2780E

DS2780E/T&R 2780 TSSOP Tape-and-Reel DS2780E+ 2780 TSSOP DS2780E+T&R 2780 TSSOP Tape-and-Reel DS2780G+ 2780 TDFN DS2780G+T&R 2780 TDFN Tape-and-Reel

+Denotes lead-free package. 1-Wire is a registered trademark of Dallas Semiconductor.

Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata

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2780 TSSOP

REV: 050907

DS2780 Standalone Fuel Gauge IC

ABSOLUTE MAXIMUM RATINGS

Voltage Range on Any Pin Relative to VSS -0.3V to +6.0V Voltage on VIN Relative to VSS -0.3V to (V

+ 0.3V)

Operating Temperature Range -40°C to +85°C Storage Temperature Range Soldering Temperature (10s)

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 the absolute maximum rating conditions for extended periods may affect device reliability.

-55°C to +125°C See JEDEC J-STD-020

RECOMMENDED DC OPERATING CHARACTERISTICS

(VDD = 2.5V to 5.5V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VDD (Note 1) +2.5 +5.5 V DQ, PIO, OVD Voltage Range

DC ELECTRICAL CHARACTERISTICS

(VDD = 2.5V to 5.5V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

(Note 1) -0.3 +5.5 V

ACTIVE Current I

SLEEP Mode Current I

ACTIVE

SLEEP

2.5V ≤ VDD ≤ 4.2V 65 95 µA

105

2.5V ≤ VDD ≤ 4.2V 1 3 µA

Input Logic High: DQ, PIO VIH (Note 1) 1.5 V

Input Logic Low: DQ, PIO VIL (Note 1) 0.6 V Output Logic Low: DQ, PIO VOL IOL = 4mA (Note 1) 0.4 V Pulldown Current: DQ, PIO IPD VDQ, V

Input Logic High: OVD VIH (Note 1)

= 0.4V 0.2 µA

PIO

VDD –

0.2

Input Logic Low: OVD VIL (Note 1) VSS + 0.2 V VIN Input Resistance RIN 15

MΩ DQ Capacitance CDQ 50 pF DQ SLEEP Timeout t Undervoltage SLEEP Threshold

DQ < VIL (Note 5) 1.5 2.0 2.5 s

SLEEP

(Note 1) 2.40 2.45 2.50 V

SLEEP

ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT

(VCC = 2.5V to 5.5V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Resolution T

Temperature Error T

Voltage Resolution V

Voltage Full-Scale VFS 0 4.992 V

0.125 °C

LSB

±3 °C

ERR

4.88 mV

LSB

Voltage Error V

Current Resolution I

±50 mV

ERR

1.56 µV

LSB

Current Full-Scale IFS ±51.2 mV

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DS2780 Standalone Fuel Gauge IC

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Current Gain Error I

Current Offset Error I

(Note 2) ±1

GERR

≤ +70°C,

- 7.82 + 12.5 µV

OERR

0°C ≤ T

2.5V ≤ VDD ≤ 4.2V (Note 4)

Accumulated Current Offset q

OERR

0°C ≤ T

2.5V ≤ VDD ≤ 4.2V VSNS = VSS, (Notes 3,

≤ +70°C,

- 188 + 0

4) VDD = 3.8V, TA = +25°C ±1

Timebase Error t

ERR

0°C ≤ TA ≤ +70°C,

2.5V ≤ VDD ≤ 4.2V

±2

±3

ELECTRICAL CHARACTERISTICS: 1-WIRE INTERFACE, STANDARD

(VCC = 2.5V to 5.5V, TA = -20°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

% Full-

Scale

µVhr/

day

Time Slot t

Recovery Time t

Write-0 Low Time t

Write-1 Low Time t

Read Data Valid t

Reset Time High t

Reset Time Low t

Presence Detect High t

Presence Detect Low t

60 120

SLOT

REC

60 120

LOW0

1 15

LOW1

RDV

480

RSTH

480 960

RSTL

15 60

PDH

60 240

PDL

ELECTRICAL CHARACTERISTICS: 1-WIRE INTERFACE, OVERDRIVE

(VCC = 2.5V to 5.5V, TA = -20°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Time Slot t

Recovery Time t

Write-0 Low Time t

Write-1 Low Time t

Read Data Valid t

Reset-Time High t

Reset-Time Low t

Presence-Detect High t

Presence-Detect Low t

6 16

SLOT

REC

6 16

LOW0

1 2

LOW1

RDV

RSTH

48 80

RSTL

2 6

PDH

8 24

PDL

μs

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DS2780 Standalone Fuel Gauge IC

EEPROM RELIABILITY SPECIFICATION

(VCC = 2.5V to 5.5V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

EEPROM Copy Time t

EEPROM Copy Endurance N

10 ms

EEC

TA = +50°C 50,000 cycles

EEC

Note 1: All voltages are referenced to VSS. Note 2: Factory calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user. Note 3: Accumulation bias register set to 00h. Note 4: Parameters guaranteed by design. Note 5: The application must wait for the maximum DQ SLEEP Timeout to confirm that the IC has entered sleep

mode.

PIN DESCRIPTION

NAME

TSSOP

NC 1 1 Not Connected. Pin not connected internally, float or connect to VSS.

VSS 2 2, 3

VIN 3 4

VDD 4 5

DQ 5 6

OVD 6 7

TDFN

FUNCTION

Device Ground. Connect directly to the negative terminal of the battery cell. Connect

the sense resistor between VSS and SNS.

Voltage Sense Input. The voltage of the battery cell is monitored through this input pin.

Power-Supply Input. Connect to the positive terminal of the battery cell through a

decoupling network.

Data Input/Output. 1-Wire data line. Open-drain output driver. Connect this pin to the

DATA terminal of the battery pack. This pin has a weak internal pulldown (IPD) for sensing pack disconnection from host or charger.

1-Wire Bus Speed Control.

Input logic level selects the speed of the 1-Wire bus.

Logic 1 selects overdrive (OVD) and Logic 0 selects standard timing (STD). On a multidrop bus, all devices must operate at the same speed.

NC — 8 Not Connected. Pin not connected internally, float or connect to VSS.

SNS 7 9

Sense Resistor Connection. Connect to the negative terminal of the battery pack.

Connect the sense resistor between VSS and SNS.

Programmable I/O Pin. Can be configured as input or output to monitor or control

PIO 8 10

user-defined external circuitry. Output driver is open drain. This pin has an weak internal pulldown (I

PAD — PAD Exposed Pad. Connect to VSS or leave floating. (Only present on TDFN package)

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Figure 1. Block Diagram

DS2780 Standalone Fuel Gauge IC

DETAILED DESCRIPTION

The DS2780 operates directly from 2.5V to 5.5V and supports single cell Lithium-ion battery packs. As shown in Figure 2, the DS2780 accommodates multicell applications by adding a voltage regulator for VDD and voltage divider for VIN. Nonvolatile storage is provided for cell compensation and application parameters. Host side development of fuel-gauging algorithms is eliminated. On-chip algorithms and convenient status reporting of operating conditions reduce the serial polling required of the host processor. For 2-cell applications, the DS2781 is recommended, since it includes a voltage regulator and accepts VIN up to 10V.

Additionally, 16 bytes of EEPROM memory are made available for the exclusive use of the host system and/or pack manufacturer. The additional EEPROM memory can be used to facilitate battery lot and date tracking and non-volatile storage of system or battery usage statistics.

A Dallas 1-Wire interface provides serial communication at the standard 16kbps or overdrive 140kbps speeds. It allows access to data registers, control registers and user memory. A unique, factory programmed 64-bit registration number (8-bit family code + 48-bit serial number + 8-bit CRC) assures that no two parts are alike and enables absolute traceability. The Dallas 1-Wire interface on the DS2780 supports multidrop capability so that multiple slave devices may be addressed with a single pin.

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Figure 2. Multicell Application Example

PK+

DS2780 Standalone Fuel Gauge IC

4.7uF0.1uF

DATA

PIO

PK-

150

PIO

(1) (1)

(1) Components improve IEC1004 Air/Contact ESD compliance

SNS

RSNS

VDD

VIN

OVD

VSS

500

0.1uF

(n * R)

Multi-Cell

Li-Ion

Battery

Protection

Circuit

Figure 3. Inside Protector Example

PK+

DATA

PIO

150

PIO

DS2780

VDD

VIN

OVD

500

Li-Ion

Battery

(1) (1)

PK-

Protection

Circuit

SNS

VSS

0.1uF

RSNS

(1) Precaution must be taken to ensure that a charge path is not created from PK+ to Data or PIO.

PROTECTOR CIRCUIT LOCATION

The battery protection circuitry can be located inside or outside the DS2780. Either location is acceptable but there are some advantages and disadvantages to both. With the protection circuit located inside, see Figure 2 and Typical Operating Circuit on page 1, the DS2780 will loose power in a circuit protection event. The DS2780 stores fuel gauge data to EEPROM, but some data loss can occur depending on the timing of the protection event and the

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DS2780 Standalone Fuel Gauge IC

backup. When the protection circuit is connected directly to the battery the protection is absolute, no charging will occur during a protection event. With the protection circuit located outside, see Figure 3, the DS2780 will remain powered up during a protection event. The disadvantage to this configuration is that you run the risk of overcharging the battery by creating an unintentional charge path from PK+ to DATA or PIO (V

PK+

> V

CELL

+ V

DIODE

Communication to the DS2780 is broken during a protection event regardless of protector location.

POWER MODES

The DS2780 has two power modes: ACTIVE and SLEEP. On initial power up, the DS2780 defaults to ACTIVE mode. While in ACTIVE mode, the DS2780 is fully functional with measurements and capacity estimation continuously updated. In SLEEP mode, the DS2780 conserves power by disabling measurement and capacity estimation functions, but preserves register contents. SLEEP mode is entered under two different conditions and an enable bit for each condition makes entry into SLEEP optional. SLEEP mode can be enabled using the Power Mode (PMOD) bit or the Under Voltage Enable (UVEN) bit.

The PMOD type SLEEP is entered if the PMOD bit is set AND DQ is low for t DQ low for t

can be used to detect a pack disconnection or system shutdown, in which no charge or discharge

SLEEP

(2s nominal). The condition of

SLEEP

current will flow. A PMOD SLEEP condition transitions back to ACTIVE mode when DQ is pulled high.

The second option for entering SLEEP is an under voltage condition. When the UVEN bit is set, the DS2780 transitions to SLEEP if the voltage on VIN is less than V logic level for t

. An under-voltage condition occurs when a pack is fully discharged, where loading on the

SLEEP

battery should be minimized. UVEN type SLEEP relieves the battery of the I

(2.45V nominal) AND DQ is stable at a low or high

SLEEP

load until communication on DQ

ACTIVE

resumes.

NOTE: PMOD and UVEN SLEEP features must be disabled when a battery is charged on an external charger that does not connect to the DQ pin. PMOD SLEEP can be used if the charger pulls DQ high. UVEN SLEEP can be used if the charger toggles DQ. The DS2780 remains in SLEEP on a charger that fails to properly drive DQ and therefore does not measure or accumulate current when a battery is charged.

INITIATING COMMUNICATION IN SLEEP

When beginning communication with a DS2780 in PMOD SLEEP, DQ must be pulled up first and then a 1-Wire Reset pulse must be issued by the master. In UVEN SLEEP, the procedure depends on the state of DQ when UVEN SLEEP was entered. If DQ was low, DQ must be pulled up and then a 1-Wire Reset pulse must be issued by the master as with PMOD SLEEP. If DQ was high when UVEN SLEEP was entered, then the DS2780 is prepared to receive a 1-Wire reset from the master. In the first two cases with DQ low during SLEEP, the DS2780

does not respond to the first rising edge of DQ with a presence pulse.

VOLTAGE MEASUREMENT

Battery voltage is measured at the VIN input with respect to VSS. It has a range of 0V to 4.992V and a resolution of 4.88mV. The measurement is stored in the VOLTAGE register in two’s compliment form and is updated every 440ms. Voltages above the maximum register value are reported at the maximum value; voltages below the minimum register value are reported at the minimum value. The format of the voltage register is shown in Figure 4.

Figure 4. Voltage Register Format

VOLT

Read Only

MSB—Address 0Ch LSB—Address 0Dh

S 2

28 27 26 25 24 23 22 21 20 X X X X X

MSb LSb MSb LSb

“S”: sign bit(s), “X”: reserved

Units: 4.88mV

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DS2780 Standalone Fuel Gauge IC

VIN is usually connected to the positive terminal of a single cell Lithium-Ion battery via a 1kΩ resistor. The input impedance is large enough (15MΩ) to be connected to a high impedance voltage divider in order to support multiple cell applications. The pack voltage should be divided by the number of series cells to present a single cell average voltage to the VIN input. In Figure 2, the value of R can be up to 1MΩ without incurring significant error due to input loading.

TEMPERATURE MEASUREMENT

The DS2780 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C. Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement form. The format of the temperature register is shown in Figure 5.

Figure 5. Temperature Register Format

TEMP

Read Only

MSB—Address 0Ah LSB—Address 0Bh

S 2

28 27 26 25 24 23 22 21 20 X X X X X

MSb LSb MSb LSb

“S”: sign bit(s), “X”: reserved

Units: 0.125°C

CURRENT MEASUREMENT

In the ACTIVE mode of operation, the DS2780 continually measures the current flow into and out of the battery by measuring the voltage drop across a low-value current-sense resistor, R

. The voltage-sense range between

SNS

SNS and VSS is ±51.2mV. The input linearly converts peak signal amplitudes up to 102.4mV as long as the continuous signal level (average over the conversion cycle period) does not exceed ±51.2mV. The ADC samples the input differentially at 18.6kHz and updates the Current register at the completion of each conversion cycle.

The Current register is updated every 3.515s with the current conversion result in two’s complement form. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).

Figure 6. Current Register Format

CURRENT

S 2

MSB—Address 0Eh LSB—Address 0Fh

213 212 211 210 29 28 27 26 25 24 23 22 21 20

MSb LSb MSb LSb

“S”: sign bit(s)

CURRENT RESOLUTION (1 LSB)

VSS VSNS

20mΩ 15mΩ 10mΩ 5mΩ

1.5625μV 78.13μA 104.2μA 156.3μA 312.5μA

AVERAGE CURRENT MEASUREMENT

Units: 1.5625μV/Rsns

SNS

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Read Only

DS2780 Standalone Fuel Gauge IC

The Average Current register reports an average current level over the preceding 28 seconds. The register value is updated every 28s in two’s complement form, and is the average of the 8 preceding Current register updates. The format of the Average Current register is shown in Figure 7. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).

Figure 7. Average Current Register Format

IAVG

S 2

MSb LSb MSb LSb

“S”: sign bit(s)

MSB—Address 08h LSB—Address 09h

213 212 211 210 29 28 27 26 25 24 23 22 21 20

Units: 1.5625μV/Rsns

Read Only

CURRENT OFFSET CORRECTION

Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements. During the offset correction conversion, the ADC does not measure the sense resistor signal. A maximum error of 1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current measurement made just prior to the offset conversion is displayed in the current register and is substituted for the dropped current measurement in the current accumulation process. This results in an accumulated current error due to offset correction of less than 1/1024.

CURRENT MEASUREMENT CALIBRATION

The DS2780’s current measurement gain can be adjusted through the RSGAIN register, which is factory-calibrated

to meet the data sheet specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or pack manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an external sense resistor’s nominal value, and allows the use of low-cost, non-precision current sense resistors. RSGAIN is an 11 bit value stored in 2 bytes of the Parameter EEPROM Memory Block. The RSGAIN value adjusts the gain from 0 to 1.999 in steps of 0.001 (precisely 2 accurate current measurement. When shipped from the factory, the gain calibration value is stored in two separate locations in the Parameter EEPROM Block, RSGAIN which is reprogrammable and FRSGAIN which is read only. RSGAIN determines the gain used in the current measurement. The read-only FRSGAIN is provided to preserve the factory value only and is not used in the current measurement.

-10

). The user must program RSGAIN cautiously to ensure

SENSE RESISTOR TEMPERATURE COMPENSATION

The DS2780 is capable of temperature compensating the current sense resistor to correct for variation in a sense resistor’s value over temperature. The DS2780 is factory programmed with the sense resistor temperature coefficient, RSTC, set to zero, which turns off the temperature compensation function. RSTC is user accessible and can be reprogrammed after module or pack manufacture to improve the current accuracy when using a high temperature coefficient current-sense resistor. RSTC is an 8-bit value stored in the Parameter EEPROM Memory Block. The RSTC value sets the temperature coefficient from 0 to +7782ppm/ºC in steps of 30.5ppm/ºC. The user must program RSTC cautiously to ensure accurate current measurement.

Temperature compensation adjustments are made when the Temperature register crosses 0.5 temperature compensation is most effective with the resistor placed as close as possible to the VSS terminal. This will optimize thermal coupling of the resistor to the on-chip temperature sensor. The current shunt trace should be run under the DS2780 package, and it should be constructed with a copper PCB trace.

C boundaries. The

CURRENT ACCUMULATION

Current measurements are internally summed, or accumulated, at the completion of each conversion period and the results are stored in the Accumulated Current Register (ACR). The accuracy of the ACR is dependent on the current measurement and the conversion timebase. The ACR has a range of 0 to 409.6mVh with an LSb of

6.25μVh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation 9 of 29

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