Table 5. resolution and range vs. sense resistor – Rainbow Electronics DS2784 User Manual
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Read and write access is allowed to the ACR. The ACR must be written MSB first then LSB. Whenever the ACR is
written, the fractional accumulation result bits are cleared. The write must be completed in 3.5s (one ACR update
period). A write to the ACR forces the ADC to perform an offset correction conversion and update the internal offset
correction factor. The current measurement and accumulation begin with the second conversion following a write to
the ACR.
The ACR value is backed up to EEPROM in case of power loss. The ACR value is recovered from EEPROM on
power-up. See Table 8 for specific address location and backup frequency.
ACCUMULATED CURRENT REGISTER FORMAT
MSB—ADDRESS
10h
LSB—ADDRESS
11h
2
15
2
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
μVh/R
SNS
Table 5. Resolution and Range vs. Sense Resistor
R
SNS
V
SS
- V
SNS
20m
Ω 15mΩ 10mΩ 5mΩ
Current Resolution
1.5625
μV 78.13μA 104.2μA 156.3μA 312.5μA
Current Range
±51.2mV ±2.56A
±3.41A ±5.12A ±10.24A
ACR Resolution
6.25
μVh 312.5μAh
416.7
μAh 625μAh
1.250mAh
ACR Range
409.6mVh 20.48Ah
27.31Ah 40.96Ah 81.92Ah
ACCUMULATION BIAS
In some designs a systematic error or an application preference requires the application of an arbitrary bias to the
current accumulation process. The current accumulation bias register (CAB) allows a user-programmed constant
positive or negative polarity bias to be included in the current accumulation process. The value in CAB can be used
to estimate battery currents that do not flow through the sense resistor, estimate battery self-discharge or estimate
current levels below the current measurement resolution. The user programmed two’s complement value, with bit
weighting the same as the current register, is added to the ACR once per current conversion cycle. The CAB is
loaded on power-up from EEPROM memory.
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 ACCUMULATION BIAS REGISTER FORMAT
ADDRESS
61h
S 2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSb
LSb
“S”: Sign Bit Units: 1.5625
μV/R
SNS