Voltage measurement, Figure 3. voltage register format, Temperature measurement – Rainbow Electronics DS2781 User Manual
Page 7: Figure 4. temperature register format, Current measurement
DS2781: Two-Cell Standalone Fuel Gauge IC
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VOLTAGE MEASUREMENT
Battery voltage is measured at the VIN input with respect to VSS over a range of 0V to 9.9902V, with a resolution
of 9.76mV. The result is updated every 440ms and placed in the VOLTAGE register in two’s compliment form.
Voltages above the maximum register value are reported at the maximum value; voltages below the minimum
register value are reported at the minimum value. The format of the voltage register is shown in Figure 3.
Figure 3. Voltage Register Format
VOLT
Read Only
MSB—Address
0Ch
LSB—Address
0Dh
S 2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
X X X X X
MSb
LSb
MSb LSb
“S”: sign bit(s), “X”: reserved
Units: 9.76mV
TEMPERATURE MEASUREMENT
The DS2781 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.
Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement
form. The format of the temperature register is shown in Figure 4.
Figure 4. Temperature Register Format
TEMP
Read Only
MSB—Address
0Ah
LSB—Address
0Bh
S 2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
X X X X X
MSb
LSb
MSb LSb
“S”: sign bit(s), “X”: reserved
Units: 0.125
°C
CURRENT MEASUREMENT
In the ACTIVE mode of operation, the DS2781 continually measures the current flow into and out of the battery by
measuring the voltage drop across a low-value current-sense resistor, R
SNS
. The voltage-sense range between
SNS and VSS is ±51.2mV. The input linearly converts peak signal amplitudes up to 102.4mV as long as the
continuous signal level (average over the conversion cycle period) does not exceed ±51.2mV. The ADC samples
the input differentially at 18.6kHz and updates the Current register at the completion of each conversion cycle.
The Current register is updated every 3.515s with the current conversion result in two’s complement form. 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).