DS2781
Figure 5. Current Register Format
CURRENT
Read Only
MSB—Address 0Eh
LSB—Address 0Fh
25 24 23 22
S
214 213 212 211 210 29
28
27
26
21 20
LSb
MSb
LSb
MSb
“S”: sign bit(s)
Units:
1.5625μV/Rsns
CURRENT RESOLUTION (1 LSB)
RSNS
VSS - VSNS
20mΩ
15mΩ
10mΩ
5mΩ
1.5625μV
78.13μA
104.2μA
156.3μA
312.5μA
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 1.56μV steps to any value between +198.1μV and -199.7μV.
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
26 25 24 23 22 21 20
LSb
MSb
“S”: sign bit(s)
Units: 1.56μV/Rsns
8 of 31
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
