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PDF DS2786B Data sheet ( Hoja de datos )
| Número de pieza | DS2786B | |
| Descripción | Stand-Alone OCV-Based Fuel Gauge | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-5223; Rev 1; 4/10
www.DataSheet4U.com
Stand-Alone OCV-Based Fuel Gauge
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 I2C 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 (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 Auxiliary 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
TEMP RANGE
PIN-PACKAGE
DS2786BG+
-20°C to +70°C 10 TDFN-EP*
DS2786BG+T&R
-20°C to +70°C 10 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
T&R = Tape and reel.
Operating Diagram
Li+
PROTECTION
CIRCUIT
VOUT
VIN
DS2786B
AIN0
AIN1
VSS
SDA
SCL
SNS
SYSTEM
μP
I2C
INTERFACE
RSNS
(EEPROM PROGRAMMING TEST POINT NOT SHOWN)
________________________________________________________________ Maxim Integrated Products 1
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.
1 page  
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Stand-Alone OCV-Based Fuel Gauge
TOP VIEW
AIN1 1
AIN0 2
SCL 3
SDA 4
SNS 5
DS2786B
EP
10 VDD
9 VIN
8 VOUT
7 VPROG
6 VSS
TDFN
(3mm x 3mm)
Pin Configuration
Pin Description
PIN NAME
1
AIN1
Auxiliary Voltage Input Number 1
2
AIN0
Auxiliary Voltage Input Number 0
FUNCTION
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. Open-drain 2-wire data line. Connect this pin to the clock signal of the 2-
wire interface. This pin has a 0.2μA typical pulldown to sense disconnection.
5 SNS Current-Sense Input. Connect to the handset side of the sense resistor.
6 VSS Device Ground. Connect to the battery side of the sense resistor.
7
VPROG
EEPROM Programming Voltage Input. Connect to external supply for production programming.
Connect to VSS during normal operation.
8
VOUT
Voltage Out. Supply for auxiliary input voltage measurement dividers. Connect to high side of
resistor-divider circuits.
9 VIN Battery Voltage Input. The voltage of the cell pack is measured through this pin.
10
VDD
Power-Supply Input. 2.5V to 4.5V Input Range. Connect to system power through a decoupling
network.
— EP Exposed Pad. Connect to VSS.
_______________________________________________________________________________________ 5
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Stand-Alone OCV-Based Fuel Gauge
Current Offset Bias
The Current Offset Bias Register (COBR) allows a pro-
grammable offset value to be added to raw current
measurements. The result of the raw current measure-
ment 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 con-
dition. The COBR value can be used to correct for a sta-
tic offset error, or can be used to intentionally skew the
current results and therefore the current accumulation.
Read and write access is allowed to COBR. Whenever
the COBR is written, the new value is applied to all sub-
sequent current measurements. COBR can be pro-
grammed in 25µV steps to any value between
+3.175mV and -3.2mV. The COBR value is stored as a
two’s-complement value in nonvolatile (NV) memory.
The COBR factory default value is 00h. Figure 9 shows
the Current Offset Bias Register format.
Current Accumulation
An Internal Accumulated Current Register (IACR)
serves as an up/down counter holding a running count
of charge since the last OCV condition. Current mea-
surement results, plus a programmable bias value are
internally summed, or accumulated, at the completion
of each current measurement-conversion period. The
IACR has a range of ±204.8mVh. The IACR uses the
Initial or Learned Cell Capacity Registers to increment
or decrement the Relative Capacity Register as current
flows into or out of the battery. In this way, the fuel
gauge is accurate even when an OCV condition does
not occur for an extended time period. See Table 2 for
the accumulated current range for various RSNS values.
ADDRESS 60h
S 26 25 24 23 22 21 20
MSB
“S”: SIGN BIT
LSB
UNITS: 25μV/RSNS
Figure 9. Current Offset Bias Register Format
Table 2. Accumulated Current Range for
Various RSNS Values
VSS - VSNS
±204.8mVh
IACR RANGE
20m
RSNS
15m
10m
±10.24Ah ±13.65Ah ±20.48Ah
5m
±40.96Ah
Cell-Capacity Estimation
The DS2786B uses a hybrid OCV measurement and
coulomb-counting algorithm to estimate remaining cell
capacity. During periods of charging or discharging the
cell, the DS2786B counts charge flow into and out of
the cell. When the application becomes inactive, the
DS2786B 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. The
resulting calculation is reported to the system as a per-
centage value between 0 and 100%. As the cell ages, a
learn feature adjusts for changes in capacity.
The Relative Capacity Register reports remaining cell
charge as a percentage of full. Relative capacity is
reported with a resolution of 0.5% and is limited to a
value between 0% and 100%. The Relative Capacity
Register is updated each time the IC performs a current
measurement or open-circuit cell-voltage measurement.
See Figure 10.
ADDRESS 02h
27 26 25 24 23 22 21 20
MSB
LSB
UNITS: 0.5%
Figure 10. Relative Capacity Register Format
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet DS2786B.PDF ] | |
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