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PDF DS2786 Data sheet ( Hoja de datos )
| Número de pieza | DS2786 | |
| Descripción | Standalone OCV-Based Fuel Gauge | |
| Fabricantes | Maxim Integrated Products | |
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www.maxim-ic.com
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
capacitywww.DataSheet4U.com 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.
APPLICATIONS
3G Multimedia Wireless Handsets
Digital Still Cameras
Digital Audio (MP3) Players
TYPICAL OPERATING CIRCUIT
DS2786
Standalone OCV-Based Fuel Gauge
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 5V Input Range
11-Bit Bidirectional Current Measurement:
25μV LSB, ±51.2mV Dynamic Range
1.67mA LSB, ±3.4A (RSNS = 15mΩ)
Current Accumulation Measurement
Resolution:
±204.8mVh Range
±13.65Ah (RSNS = 15mΩ)
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
VOUT 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
ORDERING INFORMATION
PART
DS2786G+
DS2786G+T&R
TEMP RANGE
-20ºC to +70ºC
-20ºC to +70ºC
PIN-PACKAGE
10-pin 3mm×3mm
TDFN
DS2786G+ in
Tape-and-Reel
+ Denotes lead-free package.
PIN CONFIGURATION
Commands, Registers, and Modes are capitalized for clarity.
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3mm x 3mm TDFN-10
Top View
050907
1 page  
Figure 2. Block Diagram
DS2786 Standalone 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 15mΩ sense resistor, the current sense range is ±3.4A, with a 1 LSB resolution
of 1.667mA. Current measurements are performed at regular intervals and accumulated with each measurement to
support “coulomb counting” during periods of host power consumption. Each current measurement is reported with
sign and magnitude in the two-byte Current Register. Battery voltage measurements are reported in the two-byte
Voltage Register with 12-bit (1.22mV) resolution, and auxiliary voltage measurements are reported in the two-byte
Aux Volt Registers with 11-bit resolution. Additionally, the Temperature Register reports temperature with 0.125ºC
resolution and ±3ºC accuracy from the on-chip sensor. The on-chip temperature measurement is optional and
replaces the auxiliary voltage channel AIN1.
The DS2786 provides accurate relative capacity measurements during periods of host system inactivity by looking
at cell open circuit voltage. Cell capacity is calculated using an OCV voltage profile and a 1-byte scale factor to
weight accumulated current during the coulomb-counting periods. The OCV voltage profile and scale factor are
stored in EEPROM memory. The EEPROM memory is constructed with a SRAM shadow so that the OCV voltage
profile and scale factor can be overwritten by the host to accommodate a variety of cell types and capacities from
multiple cell vendors. The I2C interface also allows read/write access to the Status, Configuration, and
Measurement Registers.
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5 Page 
Figure 10. Relative Capacity Register Format
DS2786 Standalone OCV-Based Fuel Gauge
Address 02h
27 26 25 24 23 22 21 20
MSb
LSb
Units: 0.5%
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 78.125%/Vh and a maximum range of 0 to
19921.875%/Vh. During assembly, the Initial Capacity Register should be programmed to the capacity of the cell.
For example, an application using a 1Ah cell and 0.015Ω sense resistor would set the Initial Capacity Register to a
value of (100% ÷ (1Ah × 0.015Ω)) ÷ 78.125%/Vh = 55h. The Learned Capacity Scaling Factor Register is
controlled by the DS2786. The power up value is 00h, and the register is updated with the calculated new cell
capacity value after every Learn operation.
Figure 11. Initial Capacity Scaling Factor Register Format
Address 7Ah
27 26 25 24 23 22 21 20
MSb
LSb
Units: 78.125%/Vh
Figure 12. Learned Capacity Scaling Factor Register Format
Address 19h
27 26 25 24 23 22 21 20
MSb
LSb
Units: 78.125%/Vh
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. Instead, the IACR is maintained at its present value and the DS2786 begins dV/dt
measurement evaluation to detect an OCV voltage condition. A threshold value that is below the minimum
operational current, but above the maximum idle current of the application should be selected. The Blanking/OCV
Threshold Register has a resolution of 25μV/RSNS, and a range from 0mV/RSNS to 6.375mV/RSNS. The factory
default value is 06h
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| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet DS2786.PDF ] | |
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