DS2784 Maxim Integrated Products, DS2784 Datasheet - Page 16

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

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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
Table 5. Resolution and Range vs. Sense Resistor
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
MSb
Current Resolution
Current Range
ACR Resolution
ACR Range
2
15
2
14
MSB—ADDRESS 10h
2
13
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
2
12
2
11
“S”: Sign Bit
MSb
409.6mVh
2
V
1.5625μV
±51.2mV
6.25μVh
S
10
SS
- V
2
2
SNS
9
6
LSb
2
2
8
5
16 of 37
ADDRESS 61h
312.5μAh
78.13μA
20.48Ah
±2.56A
20mΩ
2
4
MSb
2
2
3
7
Units: 1.5625μV/R
416.7μAh
104.2μA
27.31Ah
2
2
±3.41A
15mΩ
2
6
LSB—ADDRESS 11h
2
2
1
5
R
LSb
SNS
2
2
SNS
0
4
156.3μA
40.96Ah
625μAh
±5.12A
10mΩ
2
3
Units: 6.25μVh/R
2
2
1.250mAh
312.5μA
±10.24A
81.92Ah
5mΩ
2
1
LSb
2
SNS
0