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DS2780

Standalone Fuel Gauge IC

1 of 31

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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 on-

chip 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

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

2780 TSSOP

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

DQ 5

SNS 7

VDD

2 VSS

RSNS

PK+

PK-

DATA

Protection

Ci rc ui t

DS2780

PIO 8

150

1 Cell

Li-Ion

Battery

0.1uF

6 OVD

3 VIN

500

NC 1

TSSOP-8

5.6V

+Denotes lead(Pb)-free/RoHS-compliant package.

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

Summary of content (31 pages)

PAGE 1
9-4634; 5/09 DS2780 Standalone Fuel Gauge IC www.maxim-ic.com GENERAL DESCRIPTION FEATURES 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.
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DS2780 Standalone Fuel Gauge IC ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to VSS Voltage on VIN Relative to VSS Operating Temperature Range Storage Temperature Range Soldering Temperature (10s) -0.3V to +6.0V -0.3V to (VDD + 0.3V) -40°C to +85°C -55°C to +125°C See JEDEC J-STD-020 Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.
PAGE 3
DS2780 Standalone Fuel Gauge IC PARAMETER SYMBOL Current Full-Scale IFS Current Gain Error IGERR Current Offset Error IOERR Accumulated Current Offset qOERR Timebase Error tERR CONDITIONS MIN TYP (Note 2) 0°C ≤ TA ≤ +70°C, 2.5V ≤ VDD ≤ 4.2V (Note 4) 0°C ≤ TA ≤ +70°C, 2.5V ≤ VDD ≤ 4.2V VSNS = VSS, (Notes 3, 4) VDD = 3.8V, TA = +25°C MAX UNITS ±51.2 mV % FullScale ±1 -7.82 +12.5 µV -188 +0 µVhr/ day ±1 0°C ≤ TA ≤ +70°C, 2.5V ≤ VDD ≤ 4.
PAGE 4
DS2780 Standalone Fuel Gauge IC EEPROM RELIABILITY SPECIFICATION (VCC = 2.5V to 4.5V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL EEPROM Copy Time tEEC EEPROM Copy Endurance NEEC CONDITIONS TA = +50°C MIN TYP MAX UNITS 10 ms 50,000 cycles 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.
PAGE 5
DS2780 Standalone Fuel Gauge IC Figure 1. Block Diagram DETAILED DESCRIPTION The DS2780 operates directly from 2.5V to 4.5V 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.
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DS2780 Standalone Fuel Gauge IC Figure 2. Multicell Application Example PK+ 0.1uF 4.7uF 500 DATA PIO 150 DQ VDD (n * R) Multi-Cell Li-Ion Battery VIN 150 PIO (1) OVD SNS (1) R VSS Protection Circuit 0.1uF RSNS PK- (1) Components improve IEC1004 Air/Contact ESD compliance Figure 3. Inside Protector Example PK+ 500 150 DATA DQ DS2780 150 PIO PIO (1) PK- VDD (1) Protection 1K Li-Ion Battery VIN OVD SNS VSS 0.
PAGE 7
DS2780 Standalone Fuel Gauge IC fuel gauge data to EEPROM, but some data loss can occur depending on the timing of the protection event and the 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.
PAGE 8
DS2780 Standalone Fuel Gauge IC VIN is usually connected to the positive terminal of a single cell Lithium-Ion battery via a 1k resistor. The input impedance is large enough (15M) 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 1M without incurring significant error due to input loading.
PAGE 9
DS2780 Standalone Fuel Gauge IC AVERAGE CURRENT MEASUREMENT 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).
PAGE 10
DS2780 Standalone Fuel Gauge IC current measurement and the conversion timebase. The ACR has a range of 0 to 409.6mVh with an LSb of 6.25Vh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation errors. Accumulation of charge current above the maximum register value is reported at the maximum register value (7FFFh); conversely, accumulation of discharge current below the minimum register value is reported at the minimum value (8000h).
PAGE 11
DS2780 Standalone Fuel Gauge IC ACR RANGE RSNS VSS VSNS 20m 15m 10m 5m ±409.6mVh ±20.48Ah ±27.30Ah ±40.96Ah ±81.92Ah ACCUMULATION BIAS The Accumulation Bias register (AB) allows an arbitrary bias to be introduced into the current-accumulation process. The AB can be used to account for currents that do not flow through the sense resistor, estimate currents too small to measure, estimate battery self-discharge or correct for static offset of the DS2780.
PAGE 12
DS2780 Standalone Fuel Gauge IC Figure 11. Top Level Algorithm Diagram MODELING CELL CHARACTERISTICS In order to achieve reasonable accuracy in estimating remaining capacity, the cell performance characteristics over temperature, load current, and charge termination point must be considered. Since the behavior of Li-ion cells is non-linear, even over a limited temperature range of 10°C to 35°C, these characteristics must be included in the capacity estimation to achieve a reasonable accuracy.
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DS2780 Standalone Fuel Gauge IC Figure 12. Cell Model Example Diagram 100% Derivative [ppm / °C] FULL Cell Characterization data points Active Empty Standby Empty 1 0°C 2 10°C 3 20°C 4 30°C 40°C Full: The Full curve defines how the full point of a given cell depends on temperature for a given charge termination. The application’s charge termination method should be used to determine the table values.
PAGE 14
DS2780 Standalone Fuel Gauge IC CELL MODEL CONSTRUCTION The model is constructed with all points normalized to the fully charged state at +40°C. All values are stored in the cell parameter EEPROM block. The +40°C Full value is stored in uVhr with an LSB of 6.25uVhr. The +40°C Active Empty value is stored as a percentage of +40°C Full with a resolution of 2-10. Standby Empty at +40°C is by definition zero and therefore no storage is required.
PAGE 15
DS2780 Standalone Fuel Gauge IC Sense Resistor Prime (RSNSP[1/): RSNSP stores the value of the sense resistor for use in computing the absolute capacity results. The resistance is stored as a 1-byte conductance value with units of mhos (1/. RSNSP supports resistor values of 1 to 3.922m. RSNSP is located in the Parameter EEPROM block. RSNSP = 1/RSNS (units of mhos; 1/ Charge Voltage (VCHG): VCHG stores the charge voltage threshold used to detect a fully charged state.
PAGE 16
DS2780 Standalone Fuel Gauge IC “learn cycle”. First, the Active Empty Point must be detected. The Learn Flag (LEARNF) is set at this point. Then, once charging starts, the charge must continue uninterrupted until the battery is charged to full. Upon detecting full, LEARNF is cleared, the Charge to Full (CHGTF) flag is set and the Age Scalar (AS) is adjusted according to the learned capacity of the cell.
PAGE 17
DS2780 Standalone Fuel Gauge IC Read Only RAAC MSB—Address 02h 215 214 213 212 211 210 LSB—Address 03h 29 MSb 28 27 LSb MSb 26 25 24 23 22 21 20 LSb Units:1.6mAhr Remaining Standby Absolute Capacity (RSAC) [mAh] – RSAC reports the remaining battery capacity under the current temperature conditions at the Standby Empty discharge rate (ISE) to the Standby Empty point in absolute units of milli-amp-hours. RSAC is 16 bits.
PAGE 18
DS2780 Standalone Fuel Gauge IC Calculation of Results RAAC [mAh] = (ACR[mVh] - AE(T) * FULL40[mVh]) * RSNSP [mhos] Note: RSNSP = 1/RSNS RSAC [mAh] = (ACR[mVh] - SE(T) * FULL40[mVh]) * RSNSP [mhos] Note: RSNSP = 1/RSNS RARC [%] = 100% * (ACR[mVh] - AE(T) * FULL40[mVh]) / {(AS * FULL(T) - AE(T)) * FULL40[mVh]} RSRC [%] = 100%* (ACR[mVh] - SE(T) * FULL40[mVh]) / {(AS * FULL(T) - SE(T)) * FULL40[mVh]} STATUS REGISTER The STATUS register contains bits which report the device status.
PAGE 19
DS2780 Standalone Fuel Gauge IC CONTROL REGISTER All CONTROL register bits are read and write accessible. The CONTROL register is recalled from Parameter EEPROM memory at power-up. Register bit values can be modified in shadow RAM after power-up. Shadow RAM values can be saved as the power up default values by using the Copy Data command. Figure 15.
PAGE 20
DS2780 Standalone Fuel Gauge IC Figure 17. EEPROM REGISTER FORMAT Address 1Fh Bit Definition Field EEC Bit 7 Format Read Only LOCK 6 Read / Write to 1 Reserved BL1 BL0 2:6 1 Read Only 0 Read Only Allowable Values EEPROM Copy Flag Set to 1 when: Copy Data command executed Cleared to 0 when: Copy Data command completes Note: While EEC = 1, writes to EEPROM addresses are ignored Power-up default: 0 EEPROM Lock Enable Host write to 1: Enables the Lock command.
PAGE 21
DS2780 Standalone Fuel Gauge IC the RARC result crosses 4% boundaries. This allows the DS2780 to be located outside the protection FETs. In this manner, if a protection device is triggered, the DS2780 cannot lose more that 4% of charge or discharge data. Table 2.
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DS2780 Standalone Fuel Gauge IC Table 3.
PAGE 23
DS2780 Standalone Fuel Gauge IC Application Note 27, Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor Touch Memory Products. (This application note can be found on the Maxim/Dallas Semiconductor website at www.maxim-ic.com.) In the circuit in Figure 19, the shift register bits are initialized to 0. Then, starting with the least significant bit of the family code, one bit at a time is shifted in.
PAGE 24
DS2780 Standalone Fuel Gauge IC TRANSACTION SEQUENCE The protocol for accessing the DS2780 through the 1-Wire port is as follows:     Initialization Net Address Command Function Command Transaction/Data The sections that follow describe each of these steps in detail. All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the bus master followed by a presence pulse simultaneously transmitted by the DS2780 and any other slaves on the bus.
PAGE 25
DS2780 Standalone Fuel Gauge IC FUNCTION COMMANDS After successfully completing one of the net address commands, the bus master can access the features of the DS2780 with any of the function commands described in the following paragraphs. The name of each function is followed by the 8-bit opcode for that command in square brackets. The function commands are summarized in Table 4. Read Data [69h, XX]. This command reads data from the DS2780 starting at memory address XX.
PAGE 26
DS2780 Standalone Fuel Gauge IC Table 4.
PAGE 27
DS2780 Standalone Fuel Gauge IC Figure 21.
PAGE 28
DS2780 Standalone Fuel Gauge IC 1-WIRE SIGNALING The 1-Wire bus requires strict signaling protocols to ensure data integrity. The four protocols used by the DS2780 are as follows: the initialization sequence (reset pulse followed by presence pulse), write 0, write 1, and read data. All of these types of signaling except the presence pulse are initiated by the bus master. The initialization sequence required to begin any communication with the DS2780 is shown in Figure 22.
PAGE 29
DS2780 Standalone Fuel Gauge IC Figure 23.
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DS2780 Standalone Fuel Gauge IC PACKAGE INFORMATION For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. DOCUMENT NO.
PAGE 31
DS2780 Standalone Fuel Gauge IC REVISION HISTORY REVISION DATE 051209 DESCRIPTION Changed the VDD maximum operating range in the Electrical Characteristics table to 4.5V. Multicell schematic regulator changed to MAX1616 and set to 4.5V. Added “VIN pin is limited to VDD voltage” text in the Voltage Measurement section.