DS2781 Maxim Integrated Products, DS2781 Datasheet - Page 8

• Manufacturer Part Number: DS2781
• Description: 1-Cell or 2-Cell Standalone Fuel Gauge IC
• Manufacturer: Maxim Integrated Products

Figure 5. Current Register Format
CURRENT OFFSET CORRECTION
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs
approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements.
During the offset correction conversion, the ADC does not measure the sense resistor signal. A maximum error of
1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current
measurement made just prior to the offset conversion is displayed in the current register and is substituted for the
dropped current measurement in the current accumulation process. This results in an accumulated current error
due to offset correction of less than 1/1024.
CURRENT OFFSET BIAS
The Current Offset Bias (COB) register allows a programmable offset value to be added to raw current
measurements. The result of the raw current measurement plus COB is displayed as the current measurement
result in the CURRENT register, and is used for current accumulation. COB can be used to correct for a static
offset error, or can be used to intentionally skew the current results and therefore the current accumulation.
Read and write access is allowed to COB. Whenever the COB is written, the new value is applied to all subsequent
current measurements. COB can be programmed in 1.56mV steps to any value between +198.1mV and -199.7mV.
The COB value is stored as a two’s complement value in volatile memory, and must be initialized through the
interface on power-up.
Figure 6. Current Offset Bias Register Format
CURRENT
MSb
“S”: sign bit(s)
S
2
14
MSB—Address 0Eh
2
13
1.5625mV
VSNS
VSS -
2
12
2
11
MSb
“S”: sign bit(s)
78.13mA
2
20mW
S
CURRENT RESOLUTION (1 LSB)
10
2
2
9
6
LSb
2
2
8
5
104.2mA
Address 7B
8 of 30
15mW
2
4
MSb
2
2
R
3
7
SNS
Units:
2
156.3mA
2
10mW
2
6
1.56mV/Rsns
LSB—Address 0Fh
2
2
1
5
LSb
2
2
0
4
Units:
312.5mA
5mW
2
3
2
1.5625mV/Rsns
2
Read Only
2
1
LSb
2
0