Rainbow-electronics DS2781 Manual de usuario descargar pdf (Pagina 8)

DS2781: Two-Cell Standalone Fuel Gauge IC

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Figure 5. Current Register Format

CURRENT

Read Only

MSB—Address 0Eh LSB—Address 0Fh

S 2

MSb LSb MSb LSb

“S”: sign bit(s)

Units: 1.5625mV/Rsns

CURRENT RESOLUTION (1 LSB)

SNS

VSS

VSNS

20mW 15mW 10mW 5mW

1.5625mV 78.13mA 104.2mA 156.3mA 312.5mA

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

Address 7B

S 2

MSb LSb

“S”: sign bit(s) Units: 1.56mV/Rsns

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 29 30

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Rainbow-electronics DS2781 Manual de usuario Pagina 8