Datasheet

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General Description

The DS2788 measures voltage, temperature, and cur-

rent, and estimates available capacity for rechargeable

lithium-ion (Li+) and Li+ polymer batteries. Cell charac-

teristics and application parameters used in the calcu-

lations 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 cur-

rent temperature, discharge rate, stored charge, and

application parameters. Capacity estimation is reported

in mAh remaining and percentage of full.

LED display drivers and a debounced input make dis-

play of the capacity information easy. The LED pins can

directly sink current, requiring only a resistor for setting

the current in the LED display, thus reducing space and

cost.

Applications

Power Tools

Electric Bicycles

Electric Vehicles

Uninterruptible Power Supply

Digital Cameras

Features

♦ Five 30mA Open-Drain Drivers for Driving LED

Fuel-Gauge Display

♦ Debounced Fuel-Gauge Display Enable

♦ Internal Voltage Measurement Gain Register for

Trimming External Voltage-Divider

♦ Pin for Driving FETs to Enable Voltage-Divider

Only During Voltage Measurement, Conserving

Power

♦ Precision Voltage, Temperature, and Current

Measurement System

♦ Accurate, Temperature-Stable, Internal Time Base

♦ 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

♦ 14-Pin TSSOP Package

DS2788

Stand-Alone Fuel-Gauge IC with

LED Display Drivers

________________________________________________________________

Maxim Integrated Products

PIO

12 LED53DV

13 LED4

LED1

14 LED31LED2

TOP VIEW

8 VMA7DQ

9 SNS6V

10 V

5OVD

TSSOP

DS2788

Pin Configuration

Ordering Information

19-4639; Rev 2; 5/09

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.

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

T&R = Tape and reel.

Typical Operating Circuit appears at end of data sheet.

PART TEMP RANGE PIN-PACKAGE

DS2788E+ -25°C to +70°C 14 TSSOP

DS2788E+T&R -25°C to +70°C 14 TSSOP

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

Summary of content (32 pages)

PAGE 1
9-4639; Rev 2; 5/09 Stand-Alone Fuel-Gauge IC with LED Display Drivers The DS2788 measures voltage, temperature, and current, and estimates available capacity for rechargeable lithium-ion (Li+) and Li+ polymer batteries. Cell characteristics and application parameters used in the calculations are stored in on-chip EEPROM.
PAGE 2
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers ABSOLUTE MAXIMUM RATINGS Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-55°C to +125°C Soldering Temperature (10s) ................Refer to IPC/JEDEC-020 Specification. Voltage Range on Any Pin Relative to VSS..............-0.3V to +6.0V Voltage Range on VIN, VMA Relative to VSS ...-0.3V to VDD + 0.3V DVSS to VSS ..........................................................
PAGE 3
Stand-Alone Fuel-Gauge IC with LED Display Drivers DS2788 ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT (VCC = 2.5V to 4.5V, TA = -25°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Temperature Resolution TLSB Temperature Error T ERR Voltage Resolution VLSB Voltage Full-Scale VFS CONDITIONS MIN TYP MAX 0.125 °C ±3 4.88 0 UNITS °C mV 4.5 V ±50 mV ±51.
PAGE 4
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers ELECTRICAL CHARACTERISTICS: 1-Wire INTERFACE, OVERDRIVE (VCC = 2.5V to 4.5V, TA = -25°C to +70°C.
PAGE 5
Stand-Alone Fuel-Gauge IC with LED Display Drivers PIN NAME 1 LED2 Display Driver. Connect to an LED connected to VDD for display of relative pack capacity. FUNCTION 2 LED1 Display Driver. Connect to an LED connected to VDD for display of relative pack capacity. 3 DVSS 4 VDD Power-Supply Input. Connect to the positive terminal of the battery cell through a decoupling network. 5 OVD 1-Wire Bus Speed Control. Input logic level selects the speed of the 1-Wire bus.
PAGE 6
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Detailed Description The DS2788 operates directly from 2.5V to 4.5V and supports single-cell Li+ battery packs. As shown in Figure 2, the DS2788 accommodates multicell applications by adding a trim resistor for calibration of an external voltage-divider for VIN. NV storage is provided for cell compensation and application parameters. Host-side development of fuel-gauging algorithms is eliminated.
PAGE 7
Stand-Alone Fuel-Gauge IC with LED Display Drivers 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 DS2788 remains in SLEEP and therefore does not measure or accumulate current when a battery is charged on a charger that fails to properly drive DQ.
PAGE 8
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Temperature Measurement The DS2788 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 (TEMP) register in two’s complement form. Figure 4 shows the format of the Temperature register.
PAGE 9
Stand-Alone Fuel-Gauge IC with LED Display Drivers Current Offset Bias The Average Current (IAVG) 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 eight preceding Current register updates. Figure 6 shows the format of the Average Current register. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV).
PAGE 10
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers 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 2-10). The user must program RSGAIN cautiously to ensure accurate current measurement.
PAGE 11
Stand-Alone Fuel-Gauge IC with LED Display Drivers MSB—ADDRESS 12h 211 DS2788 READ ONLY ACRL 210 29 28 27 LSB—ADDRESS 13h 26 25 MSb 24 23 LSb MSb 22 21 20 X X X X LSb “X”: reserved UNITS: 1.526nVhr/RSNS ACR LSb RSNS VSS - VSNS 6.25μVh 20m 15m 10m 5m 312.5μAh 416.7μAh 625μAh 1.250mAh ACR RANGE RSNS VSS - VSNS ±409.6mVh 20m 15m 10m 5m ±20.48Ah ±27.30Ah ±40.96Ah ±81.92Ah Figure 9.
PAGE 12
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Capacity Estimation Algorithm Remaining capacity estimation uses real-time measured values and stored parameters describing the cell characteristics and application operating limits. Figure 11 describes the algorithm inputs and outputs.
PAGE 13
Stand-Alone Fuel-Gauge IC with LED Display Drivers SEGMENT 1 Full: The full curve defines how the full point of a given cell stack depends on temperature for a given charge termination. The charge termination method used in the application is used to determine the table values. The DS2788 reconstructs the full line from cell characteristic table values to determine the full capacity of the battery at each temperature. Reconstruction occurs in onedegree temperature increments.
PAGE 14
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers 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
Stand-Alone Fuel-Gauge IC with LED Display Drivers 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
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers continue uninterrupted until the battery is charged to full. Upon detecting full, LEARNF is cleared, the chargeto-full (CHGTF) flag is set, and the age scalar (AS) is adjusted according to the learned capacity of the cell. ACR Housekeeping The ACR register value is adjusted occasionally to maintain the coulomb count within the model curve boundaries.
PAGE 17
Stand-Alone Fuel-Gauge IC with LED Display Drivers MSB—ADDRESS 02h 215 DS2788 READ ONLY RAAC 214 213 212 211 LSB—ADDRESS 03h 210 29 MSb 28 27 LSb MSb 26 25 24 23 22 21 20 LSb UNITS: 1.6mAhr Figure 14. Remaining Active Absolute Capacity Register Format READ ONLY RSAC MSB—ADDRESS 04h 214 213 212 211 210 LSB—ADDRESS 05h 29 28 27 LSb MSb 26 25 24 23 22 21 20 LSb UNITS: 1.6mAhr Figure 15.
PAGE 18
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Calculation of Results RAAC [mAh] = (ACR[mVh] - AE(T) × FULL50[mVh]) × RSNSP [mhos] RSAC [mAh] = (ACR[mVh] - SE(T) × FULL50[mVh]) × RSNSP [mhos] RARC [%] = 100% × (ACR[mVh] - AE(T) × FULL50[mVh]) / {(AS × FULL(T) - AE(T)) × FULL50[mVh]} RSRC [%] = 100% × (ACR[mVh] - SE(T) × FULL50[mVh]) / {(AS × FULL(T) - SE(T)) × FULL50[mVh]} Status Register The Status register contains bits that report the device status.
PAGE 19
Stand-Alone Fuel-Gauge IC with LED Display Drivers 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 ADDRESS 60h 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.
PAGE 20
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Special Feature Register All Special Feature register bits are read and write accessible, with default values specified in each bit definition. ADDRESS 15h Field Bit Reserved 1:7 PIOSC 0 BIT DEFINITION Format Allowable Values Undefined Read/Write PIO Sense and Control Read values: 0: PIO pin VIL 1: PIO pin VIH Write values: 0: Activates PIO pin open-drain output driver, forcing the PIO pin low.
PAGE 21
Stand-Alone Fuel-Gauge IC with LED Display Drivers 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 ADDRESS Field EEC 1Fh Bit 7 LOCK 6 Reserved 2:6 BL1 BL0 1 0 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.
PAGE 22
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Memory The DS2788 has a 256-byte linear memory space with registers for instrumentation, status, and control, as well as EEPROM memory blocks to store parameters and user information. Byte addresses designated as “Reserved” return undefined data when read. Reserved bytes should not be written. Several byte registers are paired into two-byte registers in order to store 16-bit values.
PAGE 23
Stand-Alone Fuel-Gauge IC with LED Display Drivers DS2788 Table 3.
PAGE 24
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers 1-Wire Bus System The 1-Wire bus is a system that has a single bus master and one or more slaves. A multidrop bus is a 1-Wire bus with multiple slaves. A single-drop bus has only one slave device. In all instances, the DS2788 is a slave device. The bus master is typically a microprocessor in the host system.
PAGE 25
Stand-Alone Fuel-Gauge IC with LED Display Drivers Transaction Sequence The protocol for accessing the DS2788 through the 1-Wire port is as follows: • Initialization • Net Address Commands • Function Command • Transaction/Data The sections that follow describe each of these steps in detail.
PAGE 26
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Match Net Address [55h]. This command allows the bus master to specifically address one DS2788 on the 1-Wire bus. Only the addressed DS2788 responds to any subsequent function command. All other slave devices ignore the function command and wait for a reset pulse. This command can be used with one or more slave devices on the bus. Skip Net Address [CCh].
PAGE 27
Stand-Alone Fuel-Gauge IC with LED Display Drivers Lock [6Ah, XX]. This command locks (write protects) the block of EEPROM memory containing memory address XX. The lock bit in the EEPROM register must be set to 1 before the lock command is executed. To help prevent unintentional locks, one must issue the lock command immediately after setting the lock bit (EEPROM register, address 1Fh, bit 06) to a 1.
PAGE 28
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers MASTER Tx RESET PULSE DS2788 Tx PRESENCE PULSE MASTER Tx NET ADDRESS COMMAND 33h/39h READ NO NO 55h MATCH F0h SEARCH YES YES YES CCh SKIP YES NO A5h RESUME DS2788 Tx BIT 0 MASTER Tx BIT 0 YES CLEAR RESUME RESUME FLAG SET? YES DS2788 Tx SERIAL NUMBER 6 BYTES BIT O MATCH? NO NO YES DS2788 Tx CRC 1 BYTE BIT O MATCH? MASTER Tx FUNCTION COMMAND MASTER Tx FUNCTION COMMAND YES DS2788 Tx BIT 1 MASTER Tx BIT 1 DS2788 Tx BIT 1 MAS
PAGE 29
Stand-Alone Fuel-Gauge IC with LED Display Drivers Write-Time Slots A write-time slot is initiated when the bus master pulls the 1-Wire bus from a logic-high (inactive) level to a logic-low level. There are two types of write-time slots: write-1 and write-0. All write-time slots must be tSLOT in duration with a 1µs minimum recovery time, t REC , between cycles. The DS2788 samples the 1-Wire bus line between 15µs and 60µs (between 2µs and 6µs for overdrive speed) after the line falls.
PAGE 30
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers WRITE-0 SLOT WRITE-1 SLOT tSLOT tSLOT tLOW0 tLOW tREC VPULLUP GND MIN > 1μs DS2788 SAMPLE WINDOW TYP MAX MIN DS2788 SAMPLE WINDOW TYP MAX MODE: STANDARD 15μs 15μs 30μs 15μs 15μs 30μs OVERDRIVE 2μs 1μs 3μs 2μs 1μs 3μs READ-0 SLOT READ-1 SLOT tSLOT tSLOT tREC VPULLUP GND > 1μs MASTER SAMPLE WINDOW tRD MASTER SAMPLE WINDOW tRD LINE TYPE LEGEND: BUS MASTER ACTIVE LOW DS2788 ACTIVE LOW BOTH BUS MASTER AND DS2788 ACTIVE
PAGE 31
Stand-Alone Fuel-Gauge IC with LED Display Drivers PK+ 4.5V REGULATOR DISPLAY LED1 LED2 LED3 LED4 DS2788 LED5 150Ω DATA DQ SNS N-CELL Li+ BATTERY (N – 1) RΩ PIO VDD VMA VIN OVD DVSS VSS 0.1μF RΩ PROTECTION CIRCUIT 5.6V RSNS PK- Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
PAGE 32
DS2788 Stand-Alone Fuel-Gauge IC with LED Display Drivers Revision History REVISION NUMBER REVISION DATE 0 10/07 1 2 DESCRIPTION PAGES CHANGED Initial release. — 6/08 Added Figures 14 to 17 for the RAAC, RSAC, RARC, and RSRC descriptions. 17 5/09 Changed operations voltage to 4.5V maximum. 2-4, 6, 7, 31 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.