Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - battery management Charge indicator Li-Ion, Li-Po TDFN 10 EP (3x4) Surface-mount

1 of 31 REV: 062708

GENERAL DESCRIPTION

The DS2781 measures voltage, temperature, and

current, and estimates available capacity for

rechargeable Lithium-Ion and Lithium-Ion Polymer

batteries. Cell stack 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 is

reported in milliamp hours remaining and percentage

of full.

APPLICATIONS

Digital Video Cameras

Commercial Two-Way Radios

Industrial PDAs and Handheld PC Data Terminals

Portable GPS Navigation Systems

SIMPLIFIED TYPICAL OPERATING

CIRCUIT

SNS

VDD

VSS

P+

P-

Protection

Circuit

DS2781

PIO

VIN

OVD

PIN CONFIGURATIONS

VSS

VIN

VDD

PIO

SNS

OVD

PAD

VSS

VIN

VDD

PIO

SNS

OVD

TSSOP-8

3mm x 4mm TDFN-10

TOP VIEW

FEATURES

 Precision Voltage, Temperature, and Current

Measurement System

 Operates in One-Cell or Two--Cell Applications

 Accurate, Temperature Stable Internal Timebase

 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 Temperature Coefficient Calibration

Allows the Use of Low-Cost Sense Resistors

 24-Byte Parameter EEPROM

 16-Byte User EEPROM

 Unique ID and Multidrop 1-Wire® Interface

 Tiny 8-Pin TSSOP and 10-Pin TDFN (3mm x

4mm) Packages Embed Easily in Thin Prismatic

Cell Packs

ORDERING INFORMATION

PART PIN-PACKAGE TOP MARK

DS2781E+ 8 TSSOP 2781

DS2781E+T&R 8 TSSOP 2781

DS2781G+ 10 TDFN-EP* 2781

DS2781G+T&R 10 TDFN-EP* 2781

+Denotes a lead-free/RoHS-compliant package.

T&R = Tape and reel.

*EP = Exposed pad.

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

DS2781

1-Cell or 2-Cell Stand-Alone

Fuel Gauge IC

Summary of content (31 pages)

PAGE 1
DS2781 1-Cell or 2-Cell Stand-Alone Fuel Gauge IC GENERAL DESCRIPTION PIN CONFIGURATIONS The DS2781 measures voltage, temperature, and current, and estimates available capacity for rechargeable Lithium-Ion and Lithium-Ion Polymer batteries. Cell stack characteristics and application parameters used in the calculations are stored in onchip EEPROM.
PAGE 2
DS2781 ABSOLUTE MAXIMUM RATINGS Voltage Range on VDD, VIN Relative to VSS Voltage Range on Any Pin Relative to VSS Continuous Sink Current, DQ, PIO Operating Temperature Range Storage Temperature Range Soldering Temperature -0.3V to +12V -0.3V to +6.0V 20mA -40°C to +85°C -55°C to +125°C Refer to the IPC/JEDEC J-STD-020 Specification. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.
PAGE 3
DS2781 PARAMETER SYMBOL Voltage Full-Scale VFS Voltage Error VERR Current Resolution ILSB Current Full-Scale IFS Current Gain Error IGERR Current Offset Error IOERR Accumulated Current Offset qOERR Timebase Error tERR CONDITIONS MIN TYP 0 MAX UNITS 9.9902 V ±100 mV 1.56 µV ±51.2 (Note 2) 0°C ≤ TA ≤ +70°C, (Note 4) 0°C ≤ TA ≤ +70°C, VSNS = VSS (Notes 3, 4) ±1 mV % FullScale - 7.82 + 12.5 μV - 188 +0 μVhr/ day TA = +25°C, VDD = 7.
PAGE 4
DS2781 EEPROM RELIABILITY SPECIFICATION (VDD = 2.5V to 10V, 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 15 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
DS2781 Figure 1. Block Diagram VB VDD Voltage Regulator V POR BIAS/VREF Timebase EN PIO VIN DQ OVD 1-Wire Interface Status & Control Temp & Voltage ADC EEPROM SNS Accumulated Current Current ADC 15 bit + sign Rate, Temperature Compensation VSS DETAILED DESCRIPTION The DS2781 operates directly from 2.5V to 10V and supports single or dual cell Lithium-ion battery packs. Nonvolatile storage is provided for cell compensation and application parameters.
PAGE 6
DS2781 Figure 2. Typical Operating Circuit PACK+ DS2781 DATA 5.6V PACK- 500 1K 150 DQ VDD PIO VIN OVD VB SNS VSS TSSOP-8 Protection Circuit 1 or 2 Cell Li-Ion Stack 0.1uF 0.1uF RSNS POWER MODES The DS2781 has two power modes: ACTIVE and SLEEP. On initial power up, the DS2781 defaults to ACTIVE mode. While in ACTIVE mode, the DS2781 is fully functional with measurements and capacity estimation continuously updated.
PAGE 7
DS2781 VOLTAGE MEASUREMENT Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 9.9902V, with a resolution of 9.76mV. The result is updated every 440ms and placed in the VOLTAGE register in two’s complement form. 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 3. Figure 3.
PAGE 8
DS2781 Figure 5. Current Register Format Read Only CURRENT MSB—Address 0Eh S 214 213 212 211 210 LSB—Address 0Fh 29 MSb 28 27 LSb 26 25 24 23 22 MSb 21 20 LSb “S”: sign bit(s) Units: 1.5625μV/Rsns CURRENT RESOLUTION (1 LSB) VSS - VSNS 1.5625μV RSNS 20mΩ 78.13μA 15mΩ 104.2μA 10mΩ 156.3μA 5mΩ 312.5μA CURRENT OFFSET CORRECTION Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs approximately once per hour.
PAGE 9
DS2781 CURRENT MEASUREMENT CALIBRATION The DS2781’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.
PAGE 10
DS2781 update the internal offset correction factor. Current measurement and accumulation begins with the second conversion following a write to the ACR. Writing ACR clears the fractional values in ACRL. The Format of the ACR register is shown in Figure 8, and the format of ACRL is shown in Figure 9. In order to preserve the ACR value in case of power loss, the ACR value is backed up to EEPROM. The ACR value is recovered from EEPROM on power-up.
PAGE 11
DS2781 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 individual DS2781 device. The AB register allows a user programmed constant positive or negative polarity bias to be included in the current accumulation process.
PAGE 12
DS2781 Figure 11.
PAGE 13
DS2781 MODELING CELL STACK CHARACTERISTICS In order to achieve reasonable accuracy in estimating remaining capacity, the cell stack performance characteristics over temperature, load current and charge termination point must be considered. Since the behavior of Li-ion cells is non-linear, these characteristics must be included in the capacity estimation to achieve an acceptable level of accuracy in the capacity estimation.
PAGE 14
DS2781 Active Empty: The Active Empty curve defines the temperature variation in the empty point of the discharge profile based on a high level load current (one that is sustained during a high power operating mode) and the minimum voltage required for system operation. This load current is programmed as the Active Empty current (IAE), and should be a 3.
PAGE 15
DS2781 APPLICATION PARAMETERS In addition to cell model characteristics, several application parameters are needed to detect the full and empty points, as well as calculate results in mAh units. Sense Resistor Prime (RSNSP): RSNSP stores the value of the sense resistor for use in computing the absolute capacity results. The value is stored as a 1-byte conductance value with units of mhos. RSNSP supports resistor values of 1Ω to 3.922mΩ. RSNSP is located in the Parameter EEPROM block.
PAGE 16
DS2781 CAPACITY ESTIMATION UTILITY FUNCTIONS Aging Estimation As discussed above, the AS register value is adjusted occasionally based on cumulative discharge. As the ACR register decrements during each discharge cycle, an internal counter is incremented until equal to 32 times AC. AS is then decremented by one, resulting in a decrease in the scaled full battery capacity of 0.78%. Refer to the AC register description above for recommendations on customizing the age estimation rate.
PAGE 17
DS2781 RESULT REGISTERS The DS2781 processes measurement and cell characteristics on a 440ms interval and yields seven result registers. The result registers are sufficient for direct display to the user in most applications. The host system can produce customized values for system use, or user display by combining measurement, result and User EEPROM values. FULL(T) [ ]: The Full capacity of the battery at the present temperature is reported normalized to the 40°C Full value.
PAGE 18
DS2781 Remaining Active Relative Capacity (RARC) [%]: RARC reports the capacity available under the current temperature conditions at the Active Empty discharge rate (IAE) to the Active Empty point in relative units of percent. RARC is 8 bits. See Figure 16. Figure 16.
PAGE 19
DS2781 STATUS REGISTER The STATUS register contains bits that report the device status. The bits can be set internally by the DS2781. The CHGTF, AEF, SEF, LEARNF and VER bits are read only bits that can be cleared by hardware. The UVF and PORF bits can only be cleared via the 1-Wire interface. Figure 18.
PAGE 20
DS2781 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 19.
PAGE 21
DS2781 EEPROM REGISTER The EEPROM register provides access control of the EEPROM blocks. EEPROM blocks can be locked to prevent alteration of data within the block. Locking a block disables write access to the block. Once a block is locked, it cannot be unlocked. Read access to EEPROM blocks is unaffected by the lock/unlock status. Figure 21.
PAGE 22
DS2781 PARAMETER EEPROM Model data for the cells, as well as application operating parameters are stored in the Parameter EEPROM memory (block 1, addresses 60h–7Fh). The ACR (MSB and LSB) and AS registers are automatically saved to EEPROM when the RARC result crosses 4% boundaries. This allows the DS2781 to be located outside the protection FETs. In this manner, if a protection device is triggered, the DS2781 cannot lose more that 4% of charge or discharge data. Table 2.
PAGE 23
DS2781 Table 3.
PAGE 24
DS2781 In the circuit in Figure 23, 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. After the 8th bit of the family code has been entered, then the serial number is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC value. Figure 23.
PAGE 25
DS2781 TRANSACTION SEQUENCE The protocol for accessing the DS2781 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 DS2781 and any other slaves on the bus.
PAGE 26
DS2781 FUNCTION COMMANDS After successfully completing one of the net address commands, the bus master can access the features of the DS2781 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 DS2781 starting at memory address XX.
PAGE 27
DS2781 Table 4.
PAGE 28
DS2781 Figure 25.
PAGE 29
DS2781 1-Wire SIGNALING The 1-Wire bus requires strict signaling protocols to ensure data integrity. The four protocols used by the DS2781 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 DS2781 is shown in Figure 26.
PAGE 30
DS2781 Figure 27.
PAGE 31
DS2781 REVISION HISTORY REVISION DATE 062708 DESCRIPTION Added Figures 14 to 17 for the RAAC, RSAC, RARC, and RSRC descriptions. Added Package Information table. PAGES CHANGED 17, 18 30 31 of 31 Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied.