DS2745 Maxim Integrated Products, DS2745 Datasheet - Page 8

• Manufacturer Part Number: DS2745
• Description: Low-Cost I2C Battery Monitor
• Manufacturer: Maxim Integrated Products

Figure 5. TEMPERATURE REGISTER FORMAT
CURRENT MEASUREMENT
In the active mode of operation, the DS2745 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 VSS is ±51.2mV. Note that positive current values occur when
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 at with an 18.6kHz sample clock and updates
the current register at the completion of each conversion cycle. Figure 6 describes the current measurement
register format and resolution. 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).
Figure 6. CURRENT REGISTER FORMATS
Table 2. CURRENT RESOLUTION FOR VARIOUS RSNS VALUES
Table 3. CURRENT RANGE FOR VARIOUS RSNS VALUES
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 SNS to VSS signal. A maximum error of
1/1024 in the accumulated current register (ACR) is possible, however, to reduce the error, the current
measurement just prior to the offset conversion is displayed in the current register and is substituted for the
dropped current measurement in the current accumulation process. The error due to offset correction is typically
much less than 1/1024.
SNS
is less than V
CONVERSION
MSb
“S”: sign bit, “X”: reserved
MSb
“S”: sign bit
S
S
TIME
V
3.5s
±51.2mV
SS
2
2
- V
14
9
SS
SNS
MSB—Address 0A
MSB—Address 0E
, and negative current values occur when V
2
2
13
8
|V
2
2
1.5625V
12
7
SS
CURRENT INPUT RANGE
- V
±2.56A
2
20m
2
11
SNS
6
|
2
2
10
5
CURRENT RESOLUTION (1 LSB)
78.13A
20m
2
2
±3.41A
15m
4
9
LSb
LSb
2
2
3
8
8 of 15
R
104.2A
SNS
15m
±5.12A
10m
MSb
MSb
2
2
2
7
SNS
R
SNS
is greater than V
156.3A
2
2
10m
1
6
±10.24A
LSB—Address 0B
SNS
LSB—Address 0F
5m
2
2
Units:
0
5
, connected between the SNS and VSS
DS2745 Low-Cost I
2
X
4
312.5A
5m
2
SS
2
X
0
3
. Peak signal amplitudes up
= 1.5625V/Rsns
2
Units: 0.125C
X
2
www.DataSheet4U.com
2
2
X
C Battery Monitor
1
LSb
LSb
2
X
0