Datasheet

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GENERAL DESCRIPTION

The DS2786 estimates available capacity for

rechargeable Li-Ion and Li-Ion Polymer batteries

based on the cell voltage in the open-circuit state

following a relaxation period. The open-circuit voltage

(OCV) is used to determine relative cell capacity

based on a lookup table stored in the IC. This

capability makes accurate capacity information

available immediately after a battery pack is inserted.

During periods of moderate to high rate discharging,

which preclude OCV measurements, the DS2786

uses coulomb counting as a secondary means of

estimating relative capacity.

Remaining capacity is reported in percent, along with

cell voltage, current and temperature information.

Cell characteristics and application parameters used

in the calculations are stored in on-chip EEPROM.

The DS2786 is intended for use on the host side of

portable devices, though it can also be mounted

within a battery pack. Measurement and estimated

capacity data are accessed through an I

C interface.

Temperature data is available from an on-die sensor.

Resistance measurements of a pack identification

resistor and pack thermistor are supported by

ratiometric measurements on two auxiliary inputs.

APPLICATIONS

3G Multimedia Wireless Handsets

Digital Still Cameras

Digital Audio (MP3) Players

TYPICAL OPERATING CIRCUIT

FEATURES

 Relative Capacity Calculated from

Combination Coulomb Counter and Open-

Circuit Cell Voltage (OCV) Battery Model

 Accurate Warning of Low Battery Conditions

Even On First Cycle (No Learn Cycle Needed)

 12-Bit Battery Voltage Measurement:

±10mV Accuracy

1.22mV LSB, 0V to 4.5V Input Range

 11-Bit Bidirectional Current Measurement:

25V LSB, ±51.2mV Dynamic Range

1.67mA LSB, ±3.4A (R

SNS

= 15m)

 Current Accumulation Measurement

Resolution:

±204.8mVh Range

±13.65Ah (R

SNS

= 15m)

 Internal Temperature Measurement:

0.125°C LSB, ±3°C Accuracy

 Two 11-Bit Aux Input Voltage Measurements:

±8 LSB Accuracy, Ratiometric Inputs

Eliminate Supply Accuracy Issues

 V

OUT

Pin Drives Resistive Dividers, Reduces

Current Consumption

 2-Wire Interface

 Low Power Consumption:

Active Current: 50A typ, 80A max

Sleep Current: 1A typ, 3A max

ORDERING INFORMATION

PART TEMP RANGE PIN-PACKAGE

DS2786G+ -20ºC to +70ºC 10 TDFN-EP*

DS2786G+T&R -20ºC to +70ºC 10 TDFN-EP*

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

T&R = Tape and reel.

*EP = Exposed pad.

PIN CONFIGURATION

3mm x 3mm TDFN-10

Top View

DS2786

Stand-Alone OCV-Based

Fuel Gauge

www.maxim-ic.com

Commands, Registers, and Modes are capitalized for clarity.

;

Summary of content (22 pages)

PAGE 1
9-4637; 5/09 DS2786 Stand-Alone OCV-Based Fuel Gauge www.maxim-ic.com GENERAL DESCRIPTION FEATURES The DS2786 estimates available capacity for rechargeable Li-Ion and Li-Ion Polymer batteries based on the cell voltage in the open-circuit state following a relaxation period. The open-circuit voltage (OCV) is used to determine relative cell capacity based on a lookup table stored in the IC. This capability makes accurate capacity information available immediately after a battery pack is inserted.
PAGE 2
DS2786 Stand-Alone OCV-Based Fuel Gauge ABSOLUTE MAXIMUM RATINGS Voltage Range on All Pins Except VPROG Relative to VSS Voltage Range on VPROG Relative to VSS Operating Temperature Range Storage Temperature Range Soldering Temperature -0.3V to +6V -0.3V to +18V -40°C to +85°C -55°C to +125°C Refer to the IPC/JEDECJ-STD-020 Specification.
PAGE 3
DS2786 Stand-Alone OCV-Based Fuel Gauge PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 13.7 14.2 ms +3 °C VOUT Precharge Time tPRE 13.2 Temperature Error TERR -3 Input Logic High: SCL, SDA Input Logic Low: SCL, SDA Output Logic Low: SDA Pulldown Current: SCL, SDA VPROG Pulldown Input Capacitance: SCL, SDA Bus Low Timeout EEPROM Programming Voltage EEPROM Programming Current EEPROM Programming Time EEPROM Copy Endurance VIH (Note 1) 1.4 V VIL (Note 1) 0.
PAGE 4
DS2786 Stand-Alone OCV-Based Fuel Gauge PARAMETER Spike Pulse Widths Suppressed by Input Filter Capacitive Load for Each Bus Line SCL, SDA Input Capacitance Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: SYMBOL CONDITIONS tSP (Note 8) CB (Note 9) MIN 0 CBIN TYP MAX UNITS 50 ns 400 pF 60 pF All voltages are referenced to VSS. Offset specified after auto-calibration cycle and Current Offset Bias Register = 00h. The DS2786 enters the Sleep mode 1.5s to 2.
PAGE 5
DS2786 Stand-Alone OCV-Based Fuel Gauge PIN DESCRIPTION PIN 1 2 NAME AIN1 AIN0 3 SCL 4 SDA 5 6 SNS VSS 7 VPROG 8 VOUT 9 VIN 10 VDD PAD PAD FUNCTION Aux Voltage Input Number 1 Aux Voltage Input Number 0 Serial Clock Input. Input only 2-wire clock line. Connect this pin to the clock signal of the 2-wire interface. This pin has a 0.2µA typical pulldown to sense disconnection. Serial Data Input/Output. Open drain 2-wire data line. Connect this pin to the clock signal of the 2-wire interface.
PAGE 6
DS2786 Stand-Alone OCV-Based Fuel Gauge DESCRIPTION The DS2786 provides current-flow, voltage, and temperature measurement data to support battery-capacity monitoring in cost-sensitive applications. Current is measured bidirectionally over a dynamic range of ±51.2mV with a resolution of 25µV. Assuming a 15m sense resistor, the current sense range is ±3.4A, with a 1 LSB resolution of 1.667mA.
PAGE 7
DS2786 Stand-Alone OCV-Based Fuel Gauge POWER MODES The DS2786 operates in one of two power modes: Active and Sleep. While in Active mode, the DS2786 operates as a high-precision battery monitor with temperature, voltage, auxiliary inputs, current, and accumulated current measurements acquired continuously and the resulting values updated in the Measurement Registers. In Sleep mode, the DS2786 operates in a low-power mode with no measurement activity.
PAGE 8
DS2786 Stand-Alone OCV-Based Fuel Gauge VOLTAGE MEASUREMENT Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 4.5V and with a resolution of 1.22mV. The result is updated every 880ms and placed in the Voltage Register in two’s complement form. Voltages above the maximum register value are reported as 7FFFh. Figure 5. Voltage Register Format MSB—Address 0Ch S 211 210 29 28 LSB—Address 0Dh 27 26 MSb 25 24 LSb 23 22 21 20 X X MSb X LSb Units: 1.
PAGE 9
DS2786 Stand-Alone OCV-Based Fuel Gauge TEMPERATURE MEASUREMENT The DS2786 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C. Temperature measurements are updated every 1760ms and placed in the Temperature Register in two’s complement form. The format of the Temperature Register is shown in Figure 7. The ITEMP bit in the Status/Configuration Register must be set to enable the internal temperature measurement instead of the AIN1 measurement. Figure 7.
PAGE 10
DS2786 Stand-Alone OCV-Based Fuel Gauge Table 1. Current Range and Resolution for Various RSNS Values CURRENT RESOLUTION (1 LSB) RSNS |VSS - VSNS| 20m 1.25mA 25V 15m 1.667mA 10m 2.5mA 5m 5mA CURRENT INPUT RANGE RSNS VSS - VSNS 20m ±2.56A ±51.2mV 15m ±3.41A 10m ±5.12A 5m ±10.24A CURRENT OFFSET BIAS The Current Offset Bias Register (COBR) allows a programmable offset value to be added to raw current measurements.
PAGE 11
DS2786 Stand-Alone OCV-Based Fuel Gauge CELL CAPACITY ESTIMATION The DS2786 uses a hybrid OCV measurement and coulomb counting algorithm to estimate remaining cell capacity. During periods of charging or discharging of the cell, the DS2786 counts charge flow into and out of the cell. When the application becomes inactive, the DS2786 waits for the cell voltage to relax and then adjusts the coulomb count based on an open-circuit voltage cell model stored in device EEPROM.
PAGE 12
DS2786 Stand-Alone OCV-Based Fuel Gauge OCV DETECTION AND CURRENT BLANKING The Blanking/OCV Threshold Register sets the current measurement level at which the DS2786 switches between coulomb counting and open-circuit voltage measurement. When the magnitude of the measured current (after COBR is applied) is less than the value defined by the Blanking/OCV Threshold Register, the measurement is not summed into the IACR.
PAGE 13
DS2786 Stand-Alone OCV-Based Fuel Gauge OCV CELL MODEL The OCV cell model is a 9-point piece-wise linear approximation of open circuit cell voltage versus the remaining capacity of the cell. Whenever an OCV update occurs, the Relative Capacity Register is adjusted to a new value based on the OCV voltage reading and a linear approximation of the table values. Figure 15 shows the factorydefault cell model stored in EEPROM. Figure 15. Default OCV Cell Model 4.2 Breakpoint 7 4.087V 90.5% Breakpoint 4 3.
PAGE 14
DS2786 Stand-Alone OCV-Based Fuel Gauge Figure 17. Voltage Breakpoint Register Format MSB—Even Addresses 68h–78h 211 210 29 28 27 26 25 MSb LSB—Odd Address 69h–79h 24 LSb 23 22 21 20 X X X MSb X LSb Units: 1.22mV “X”: reserved INITIAL CAPACITY ESTIMATION The DS2786 calculates Relative Capacity immediately upon power up. During initialization, the DS2786 makes a voltage measurement and uses the OCV cell model data to determine a starting point for the Relative Capacity Register.
PAGE 15
DS2786 Stand-Alone OCV-Based Fuel Gauge Figure 19. Last OCV Register Format Address 16h 27 26 25 24 23 22 21 MSb Units: 20 LSb 0.5% The Learn Delta Percent Threshold allows the application to select how large of a cell capacity change is required before the new cell capacity value is learned. The difference between the present OCV measurement and the Last OCV measurement must be greater than the Learn Delta Percent Threshold value for a Learn to occur.
PAGE 16
DS2786 Stand-Alone OCV-Based Fuel Gauge Table 3.
PAGE 17
DS2786 Stand-Alone OCV-Based Fuel Gauge STATUS/CONFIG REGISTER The Status/Config Register is read/write with individual bits designated as read only. Bit values indicate status as well as program or select device functionality. Bits 3 though 6 are EEPROM backed at memory location 7Ch. Note that their bit positions differ between these locations. Figure 22.
PAGE 18
DS2786 Stand-Alone OCV-Based Fuel Gauge COMMAND REGISTER The Command Register is read/write accessible. Bit values indicate operations requested to be performed by the device. Figure 23. Command Register Format ADDRESS Feh BIT 7 POR BIT 6 0 BIT 5 X BIT 4 X BIT 3 POCV BIT 2 SOCV BIT 1 RCALL BIT 0 COPY Bit 7: POR—Power-On Reset. A value of 1 starts a power-on reset event. The bit is cleared on the next start or stop on the 2-Wire bus, exiting the reset state. Bit 6: 0—Bit always reads logic 0.
PAGE 19
DS2786 Stand-Alone OCV-Based Fuel Gauge Bus Idle The bus is defined to be idle, or not busy, when no master device has control. Both SDA and SCL remain high when the bus is idle. The STOP condition is the proper method to return the bus to the idle state. START and STOP Conditions The master initiates transactions with a START condition (S), by forcing a high-to-low transition on SDA while SCL is high.
PAGE 20
DS2786 Stand-Alone OCV-Based Fuel Gauge Read/Write Bit The R/W bit following the slave address determines the data direction of subsequent bytes in the transfer. R/W = 0 selects a write transaction, with the following bytes being written by the master to the slave. R/W = 1 selects a read transaction, with the following bytes being read from the slave by the master. With the ADDR3–ADDR0 bits at their default of 0110, writes occur using address 0x6Ch, while reads occur at 0x6Dh.
PAGE 21
DS2786 Stand-Alone OCV-Based Fuel Gauge Write Data Protocol The write data protocol is used to write to register and shadow RAM data to the DS2786 starting at memory address Maddr. Data0 represents the data written to Maddr, Data1 represents the data written to Maddr + 1 and DataN represents the last data byte, written to Maddr + N. The master indicates the end of a write transaction by sending a STOP or Repeated START after receiving the last acknowledge bit.
PAGE 22
DS2786 Stand-Alone OCV-Based Fuel Gauge REVISION HISTORY REVISION DATE 030708 DESCRIPTION PAGES CHANGED In the Recommended DC Operating Characteristics, changed the PIO pin range to VPROG pin range and changed the operating range to 15.5V. 2 Corrected bit locations of VDIS and LODIS bits in EEPROM (Figure 14 and Status/Config Register section). 12, 17 Fixed grammatical error under OCV cell model section: “required” to “require.