Manual
DS2740
5 of 15
CURRENT RESOLUTION (1 LSB)
R
SNS
PART
CONVERSION
TIME
V
IS1
- V
IS2
20mW 15mW 10mW 5mW
DS2740
3.515s
1.5625mV 78.13mA 104.2mA 156.3mA 312.5mA
DS2740B
0.878s
6.250mV 312.5mA 416.7mA 625mA
1.250mA
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset
correction occurs approximately once per hour in the DS2740 and four times per hour in the DS2740B.
The resulting correction factor is applied to the subsequent 1023 measurements. During the offset
correction conversion, the ADC does not measure the IS1 to IS2 signal. A maximum error of 1/1024 in
the accumulated current register (ACR) is possible, however, to reduce the error, the current measurement
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. The typical error due to offset correction is
much less than 1/1024.
CURRENT ACCUMULATOR
Current measurements are internally summed, or accumulated, at the completion of each conversion
period with the results displayed in the ACR. The accuracy of the ACR is dependent on both the current
measurement and the conversion timebase. The ACR has a range of ±204.8mVh with an LSb of
6.25µVh. Additional registers hold fractional results of each accumulation, however, these bits are not
user accessible.
Read and write access is allowed to the ACR. Whenever the ACR is written, fractional accumulation
results are cleared. Also, a write forces the ADC to measure its offset and update the offset correction
factor. The current measurement and accumulation begin with the second conversion following a write to
the ACR. Figure 4 describes the ACR address, format, and resolution.
Figure 4. CURRENT ACCUMULATOR FORMAT
MSB—Address 10 LSB—Address 11
S2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSb LSb MSb LSb
Units: 6.25
m
Vh/Rsns
ACR LSB
R
SNS
PART
UPDATE
INTERVAL
V
IS1
- V
IS2
20mW 15mW 10mW 5mW
DS2740
3.515s
DS2740B
0.878s
6.25mVh 312.5mAh 416.7mAh 625mAh
1.250mAh