DS2786BG+ Maxim Integrated Products, DS2786BG+ Datasheet - Page 12

• Manufacturer Part Number: DS2786BG+
• Description: IC FUEL GAUGE OCV-BASED 10-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of DS2786BG+

• Function: Fuel, Gas Gauge/Monitor
• Battery Type: Lithium-Ion (Li-Ion), Lithium-Polymer (Li-Pol)
• Voltage - Supply: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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 rela-
tive capacity (16h). After the first learn operation, the rel-
ative 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 x 0.015Ω))/
78.125%/Vh = 55h. The Learned Capacity Scaling Factor
Register is controlled by the DS2786B. The power-up
value is 00h, and the register is updated with the calcu-
lated new cell capacity value after every learn operation.
See Figures 11 and 12.
When the magnitude of the measured current (after
COBR is applied) is less than the value defined by the
OCV Threshold Register, the DS2786B begins dV/dt
measurement evaluation to detect an OCV voltage
condition. A threshold value that is below the minimum
Figure 11. Initial Capacity Scaling Factor Register Format
Figure 12. Learned Capacity Scaling Factor Register Format
12
MSB
MSB
2
2
7
7
______________________________________________________________________________________
2
2
6
6
2
2
5
5
ADDRESS 7Ah
ADDRESS 17h
2
2
4
4
2
2
3
3
OCV Detection
UNITS: 78.125%/Vh
UNITS: 78.125%/Vh
2
2
2
2
2
2
1
1
LSB
LSB
2
2
0
0
operational current, but above the maximum idle cur-
rent of the application should be selected. The OCV
Threshold Register has a resolution of 25µV/R
a range from 0mV/R
default value is 28h. See Figure 13 for the OCV thresh-
old register format.
While the measured current is below the OCV threshold
level, the DS2786B actively searches for a relaxed cell
by calculating the change in cell voltage as reported in
the Voltage Register over 7.5min intervals (dV/dt). If the
7.5min dV/dt change of an average of four Voltage
Register readings is less than the value stored in the
OCV dV/dt Threshold Register, the DS2786B deter-
mines that the cell is now in a relaxed state and the
Relative Capacity Register is adjusted based on the
OCV cell model stored in parameter EEPROM. This
operation occurs repeatedly every 7.5min up to 1hr
after the cell enters a relaxed state.
The OCV dV/dt Threshold Register has a resolution of
0.61mV/7.5min and a range from 0mV/7.5min to
9.15mV/7.5min. The factory default value is
2.44mV/7.5min. Note that the upper 4 bits of the OCV
dV/dt Threshold Register are used to EEPROM back
bits from the Status/Configuration Register. Figure 14
shows the OCV dV/dt threshold register format.
Figure 13. OCV Threshold Register Format
Figure 14. OCV dV/dt Threshold Register Format
SMOD
MSB
MSB
2
7
LDIS VODIS ITEMP
2
6
2
5
SNS
ADDRESS 7Ch
ADDRESS 7Bh
2
4
to 6.375mV/R
2
3
2
3
UNITS: 0.61mV/7.5min
2
UNITS: 25μV/R
2
2
SNS
2
. The factory
2
2
1
1
SNS
LSB
LSB
2
, and
SNS
2
0
0