Datasheet

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

General Description

The DS2786B estimates available capacity for recharge-

able Li-ion (Li+) and Li+ polymer batteries based on the

cell voltage in the open-circuit state following a relax-

ation 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 dis-

charging, which preclude OCV measurements, the

DS2786B 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 DS2786B 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 mea-

surements of a pack identification resistor and pack ther-

mistor are supported by ratiometric measurements on

two auxiliary inputs.

The DS2786B comes in a 10-pin, lead-free, TDFN 3mm

x 3mm package with an exposed pad (EP).

Applications

3G Multimedia Wireless Handsets

Digital Still Cameras

Digital Audio (MP3) Players

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

25µV LSB, ±51.2mV Dynamic Range

1.67mA LSB, ±3.4A (R

SNS

= 15mΩ)

♦ Current Accumulation Measurement Resolution

±204.8mVh Range

±13.65Ah (R

SNS

= 15mΩ)

♦ Internal Temperature Measurement

0.125°C LSB, ±3°C Accuracy

♦ Two 11-Bit Auxiliary 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: 50µA (typ), 80µA (max)

Sleep Current: 1µA (typ), 3µA (max)

DS2786B

Stand-Alone OCV-Based Fuel Gauge

________________________________________________________________

Maxim Integrated Products

Ordering Information

SNS

AIN0

OUT

AIN1

SDA

SCL

Li+

PROTECTION

CIRCUIT

THERMISTOR

PACKID

INTERFACE

SYSTEM

μP

SNS

(EEPROM PROGRAMMING TEST POINT NOT SHOWN)

DS2786B

Operating Diagram

19-5223; Rev 1; 4/10

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.

EP = Exposed pad.

T&R = Tape and reel.

PART TEMP RANGE PIN-PACKAGE

DS2786BG+ -20°C to +70°C 10 TDFN-EP*

DS2786BG+T&R -20°C to +70°C 10 TDFN-EP*

Summary of content (21 pages)

PAGE 1
9-5223; Rev 1; 4/10 Stand-Alone OCV-Based Fuel Gauge Features The DS2786B 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 I2C 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.
PAGE 2
DS2786B Stand-Alone OCV-Based Fuel Gauge ABSOLUTE MAXIMUM RATINGS Voltage on All Pins Except VPROG Relative to VSS ...-0.3V to +6V Voltage on VPROG Relative to VSS ..........................-0.3V to +18V Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-55°C to +125°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) .......................................
PAGE 3
Stand-Alone OCV-Based Fuel Gauge (2.5V ≤ VDD ≤ 4.5V, TA = -20°C to +70°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Logic-High: SCL, SDA VIH (Note 1) Input Logic-Low: SCL, SDA VIL (Note 1) 0.6 V Output Logic-Low: SDA VOL IOL = 4mA (Note 1) 0.4 V IPD VDD = 4.2V, VPIN = 0.4V Pulldown Current: SCL, SDA VPROG Pulldown 1.4 0.
PAGE 4
DS2786B Stand-Alone OCV-Based Fuel Gauge ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (continued) (2.5V ≤ VDD ≤ 4.5V, TA = -20°C to +70°C.) Note 6: The maximum tHD:DAT has only to be met if the device does not stretch the low period (tLOW) of the SCL signal. Note 7: This device internally provides a hold time of at least 100ns for the SDA signal (referred to the VIHMIN of the SCL signal) to bridge the undefined region of the falling edge of SCL.
PAGE 5
Stand-Alone OCV-Based Fuel Gauge TOP VIEW AIN1 1 10 VDD AIN0 2 9 VIN SCL 3 8 VOUT 7 VPROG 6 VSS DS2786B SDA 4 SNS 5 EP TDFN (3mm x 3mm) Pin Description PIN NAME FUNCTION 1 AIN1 Auxiliary Voltage Input Number 1 2 AIN0 Auxiliary Voltage Input Number 0 3 SCL 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. 4 SDA Serial Data Input/Output.
PAGE 6
DS2786B Stand-Alone OCV-Based Fuel Gauge Detailed Description The DS2786B provides current-flow, voltage, and temperature-measurement data to support batterycapacity monitoring in cost-sensitive applications. Current is measured bidirectionally over a dynamic range of ±51.2mV with a resolution of 25µV. Assuming a 15mΩ sense resistor, the current-sense range is ±3.4A, with a 1 least significant bit (LSB) resolution of 1.667mA.
PAGE 7
Stand-Alone OCV-Based Fuel Gauge SYSTEM SYSTEM VDD PACK+ 150Ω 1kΩ VOUT VIN VDD 1kΩ 10nF (1) 5.6V VPROG AIN0 SDA AIN1 1kΩ SCL VSS RSNS 1nF (1) OPTIONAL FOR 8kV/15kV ESD SYSTEM SERIAL BUS SNS PROTECTION IC (Li+/POLYMER) PACK- PROGRAMMING TEST POINT DS2786B PACKID THERM DS2786B BATTERY 2.5V SYSTEM VSS (1) 1nF Figure 3. Application Example The DS2786B provides accurate relative capacity measurements during periods of host system inactivity by looking at cell open-circuit voltage.
PAGE 8
DS2786B Stand-Alone OCV-Based Fuel Gauge Parameter Measurement The DS2786B uses a sigma-delta A/D converter to make measurements. The measurement sequence shown in Figure 4 repeats continuously while the DS2786B is in Active Mode. The VOUT pin is activated tPRE before the AIN0 and AIN1 conversion to allow for VIN PIN MEASUREMENT the VOUT output voltage to settle. The DS2786B can be configured to measure temperature using its on-chip sensor instead of the AIN1 input.
PAGE 9
Stand-Alone OCV-Based Fuel Gauge conversion is displayed in the Voltage Register. The OCV algorithm automatically adjusts for the effects of the offset-correction cycle. Battery voltage is measured at the VIN input with respect to VSS over a 0 to 4.999V range 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 is the Voltage Register format.
PAGE 10
DS2786B Stand-Alone OCV-Based Fuel Gauge Temperature Measurement The DS2786B 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.
PAGE 11
Stand-Alone OCV-Based Fuel Gauge The Current Offset Bias Register (COBR) allows a programmable offset value to be added to raw current measurements. The result of the raw current measurement plus the COBR value is displayed as the current measurement result in the Current Register, and is used for current accumulation and detection of an OCV condition.
PAGE 12
DS2786B Stand-Alone OCV-Based Fuel Gauge Prior to the first learn operation, the relative capacity value is calculated by adding the IACR multiplied by the initial capacity scaling factor (7Ah) to the last OCV relative capacity (16h). After the first learn operation, the relative capacity value is calculated by adding the IACR multiplied by the learned capacity scaling factor (17h) to the last OCV relative capacity (16h). Each Capacity Scaling Factor Register has a resolution of 78.
PAGE 13
Stand-Alone OCV-Based Fuel Gauge The OCV cell model is a 9-point piece-wise linear approximation of open-circuit cell voltage vs. 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 factory-default cell model stored in EEPROM. The OCV cell model can be modified by changing the Capacity and Voltage Breakpoint Registers in EEPROM.
PAGE 14
DS2786B Stand-Alone OCV-Based Fuel Gauge MSB—EVEN ADDRESSES 68h–78h 211 210 29 28 27 26 LSB—ODD ADDRESS 69h–79h 25 MSB 24 23 LSB 22 21 20 X X X MSB X LSB “X”: RESERVED UNITS: 1.22mV Figure 17. Voltage Breakpoint Register Format Initial Capacity Estimation The DS2786B calculates relative capacity immediately upon power-up. During initialization, the DS2786B makes a voltage measurement and uses the OCV cell model data to determine a starting point for the Relative Capacity Register.
PAGE 15
Stand-Alone OCV-Based Fuel Gauge 27 26 25 24 23 22 21 20 MSB LSB UNITS: 0.5% Figure 20. Learn Delta Percent Threshold The learn delta percent threshold allows the application to select how large 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
DS2786B Stand-Alone OCV-Based Fuel Gauge Table 3.
PAGE 17
Stand-Alone OCV-Based Fuel Gauge 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. See Figure 22: • PORF—The power-on-reset flag is set to indicate initial power-up. PORF is not cleared internally.
PAGE 18
DS2786B Stand-Alone OCV-Based Fuel Gauge • COPY—The Copy bit is set to start a copy command of the scratchpad to EEPROM. A programming voltage must be present on the VPROG pin prior for the copy to be successful. The Copy bit must be cleared by software within the tPROG time window. • RCALL—The Recall bit is set to recall the contents of EEPROM into the scratchpad. • SOCV—Stored OCV calculation.
PAGE 19
Stand-Alone OCV-Based Fuel Gauge Bus Timing The DS2786B is compatible with any bus timing up to 400kHz. No special configuration is required to operate at any speed. 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.
PAGE 20
DS2786B Stand-Alone OCV-Based Fuel Gauge Basic Transaction Formats Write: S SAddr W A MAddr A Data0 A P A write transaction transfers 1 or more data bytes to the DS2786B. The data transfer begins at the memory address supplied in the MAddr byte. Control of the SDA signal is retained by the master throughout the transaction, except for the acknowledge cycles. Read: SAddr W A MAddr A Sr SAddr R A Data0 N P Write Portion Read Portion A read transaction transfers 1 or more bytes from the DS2786B.
PAGE 21
Stand-Alone OCV-Based Fuel Gauge REVISION NUMBER REVISION DATE 0 7/08 Initial release 1 4/10 Changed the maximum operating voltage on VDD to 4.5V in the Features, Electrical Characteristics, and Pin Description sections DESCRIPTION PAGES CHANGED — 1–5 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.