ds2786 Maxim Integrated Products, Inc., ds2786 Datasheet - Page 9

• Manufacturer Part Number: ds2786
• Description: Ds2786 Standalone Ocv-based Fuel Gauge
• Manufacturer: Maxim Integrated Products, Inc.

CURRENT MEASUREMENT
In the Active mode of operation, the DS2786 continually measures the current flow into and out of the battery by
measuring the voltage drop across a low-value current-sense resistor, R
pins. The voltage sense range between SNS and V
V
to 102mV are allowed at the input as long as the continuous or average signal level does not exceed ±51.2mV over
the conversion cycle period. The ADC samples the input differentially and updates the Current Register every
880ms at the completion of each conversion cycle. Figure 8 describes the Current Measurement Register format
and resolution for each option. Charge currents above the maximum register value are reported at the maximum
value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum
value (8000h = -51.2mV).
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction to improve Current
accuracy. Offset correction occurs approximately every 15 minutes. The resulting correction factor is applied to the
subsequent 1023 measurements. During the offset correction conversion, the ADC does not make a measurement.
The current measurement just prior to the offset conversion is displayed in the Current Register.
Figure 8. Current Register Formats
Table 1. Current Range and Resolution for Various R
CURRENT OFFSET BIAS
The Current Offset Bias Register (COBR) allows a programmable offset value to be added to raw current
measurements. The result of the raw current measurement plus the COBR value is displayed as the current
measurement result in the Current Register, and is used for current accumulation and detection of an OCV
condition. The COBR value 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 COBR. Whenever the COBR is written, the new value is applied to all
subsequent current measurements. COBR can be programmed in 25μV steps to any value between +3.175mV
and -3.2mV. The COBR value is stored as a two’s complement value in nonvolatile (NV) memory. The COBR
factory default value is 00h.
SNS
is less than V
MSb
“S”: sign bit
S
2
10
SS
MSB—Address 0Eh
CURRENT RESOLUTION (1 LSB)
CURRENT INPUT RANGE
, and negative current values occur when V
2
9
|V
V
±51.2mV
SS
SS
2
25µV
8
- V
- V
SNS
SNS
2
7
|
2
6
2
1.25mA
±2.56A
20mΩ
5
20mΩ
LSb
2
4
SS
9 of 22
is ±51.2mV. Note that positive current values occur when
1.667mA
±3.41A
15mΩ
15mΩ
MSb
2
3
SNS
R
SNS
R
is greater than V
2
SNS
SNS
2
LSB—Address 0Fh
2.5mA
±5.12A
Values
10mΩ
10mΩ
SNS
2
1
, connected between the SNS and V
2
0
SS
±10.24A
X
5mΩ
5mA
5mΩ
. Peak signal amplitudes up
Units: 25μV/R
X
X
LSb
X
SNS
SS