Temperature measurement, Current measurement – Rainbow Electronics DS2784 User Manual
Page 13
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TEMPERATURE MEASUREMENT
The DS2784 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.
TEMPERATURE REGISTER FORMAT
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
Note:
Temperature and battery voltage (V
IN
) are measured using the same ADC. Therefore, measurements are a 220ms average updated
every 440ms.
CURRENT MEASUREMENT
The DS2784 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 V
SS
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 (3.52s). Charge currents above the
maximum register value are reported as 7FFFh. Discharge currents below the minimum register value are reported
as 8000h.
CURRENT REGISTER FORMAT
MSB—ADDRESS
0Eh
LSB—ADDRESS
0Fh
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
“S”: Sign Bit(s)
Units: 1.5625
μV/R
SNS
The average current register reports an average current level over the preceding 28s. The register value is updated
every 28s in two’s complement form, and represents an average of the eight preceding current register values.
AVERAGE CURRENT REGISTER FORMAT
MSB—ADDRESS
08h
LSB—ADDRESS
09h
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
“S”: Sign Bit(s)
Units: 1.5625
μV/R
SNS
CURRENT OFFSET CORRECTION
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs
approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements.
During the offset correction conversion, the ADC does not measure the sense-resistor signal. A maximum error of
1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current