Figure 5. accumulated current register format, Offset accumulation blanking, Accumulation bias – Rainbow Electronics DS2756 User Manual
Page 8
DS2756: High-Accuracy Battery Fuel Gauge with Programmable Suspend Mode
8 of 26
command targeting the ACR register address. A write to the ACR results in an automatic copy of the new value to
EEPROM.
Figure 5. Accumulated Current Register Format
MSB-Address
10h LSB-Address
11h
S 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
mVh/Rsns
ACR LSB
R
SNS
V
IS1
- V
IS2
20m
W 15mW 10mW 5mW
6.25
mVh 312.5mAh 416.7mAh 625mAh
1.250mAh
ACR RANGE
R
SNS
V
IS1
- V
IS2
20m
W 15mW 10mW 5mW
±204.8mVh ±10.24Ah ±13.65Ah ±20.48Ah ±40.96Ah
OFFSET ACCUMULATION BLANKING
In order to avoid the accumulation of small positive offset errors over long periods, an offset blanking filter is
provided. The blanking filter is enabled by setting the OBEN bit in the Status Register. When OBEN is set, charge
currents (positive Current register values) between 15.625
mV and 62.5mV are not accumulated in the ACR.
Therefore, with RSNS=0.020
W, positive currents between 0.78mA and 3.125mA are blanked from accumulation in
the ACR.
ACCUMULATION BIAS
Systematic errors or an application preference can require the application of an arbitrary bias to the current
accumulation process. The Accumulation Bias register is provided to allow a user programmed constant positive or
negative polarity bias to the current accumulation process. The Accumulation Bias value can be used to estimate
battery currents that do not flow through the sense resistor, estimate battery self-discharge, or correct for offset
error in the Current register and ACR register. The user programmed two’s complement value in the Accumulation
Bias register is added to the Current Register once per current sample. The register format supports the
accumulation bias to be applied in 1.95
mV increments over a ±250mV range. When using a 20mW sense resistor,
the bias control is 100
mA over a ±12.5mA range.
The Accumulation Bias register is directly read and write accessible. The user value is made non-volatile with a
Copy Data command targeting EEPROM block 0. The Accumulation Bias register is loaded from EEPROM
memory on power up and a transition from Sleep to Active mode.