DS2784 Maxim Integrated Products, DS2784 Datasheet - Page 14

• Manufacturer Part Number: DS2784
• Description: 1-Cell Stand-Alone Fuel Gauge IC
• Manufacturer: Maxim Integrated Products

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The average current register reports an average current level over the preceding 28s. The register value is updated
every 28s in two’s complement form, and represents an average of the eight preceding current register values.
AVERAGE 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 retained in the current register and is substituted for the
dropped current measurement in the current accumulation process. Therefore, the accumulated current error due
to offset correction is typically much less than 1/1024.
CURRENT OFFSET BIAS
The current offset bias (COB) value 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 1.56μV steps to any value between +198.1µV and -199.7µV.
The COB value is stored as a two’s complement value in EEPROM. The COB is loaded on power-up from
EEPROM memory. The factory default value is 00h.
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents
between 100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV
and -25µV are accumulated if they are made by the CAB.
CURRENT OFFSET BIAS REGISTER FORMAT
CURRENT BLANKING
The current blanking feature modifies current measurement result prior to being accumulated in the ACR. Current
blanking occurs conditionally when a current measurement (raw current + COBR) falls in one of two defined
ranges. The first range prevents charge currents less than 100μV from being accumulated. The second range
prevents discharge currents less than 25μV in magnitude from being accumulated. Charge current blanking is
always performed; however, discharge current blanking must be enabled by setting the NBEN bit in the control
register. See the register description for additional information.
MSb
“S”: Sign Bit(s)
S
2
14
MSB—ADDRESS 08h
2
13
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
2
12
2
11
MSb
“S”: Sign Bit(s)
2
S
10
2
2
9
6
LSb
2
2
8
5
14 of 37
ADDRESS 7Bh
2
4
MSb
2
2
3
7
Units: 1.56μV/R
2
2
2
6
LSB—ADDRESS 09h
2
2
1
5
LSb
2
2
SNS
0
4
2
3
Units: 1.5625μV/R
2
2
2
1
LSb
2
SNS
0