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ADT7481ARMZ-1R7 Dual Channel Temperature Sensor and Overtemperature Alarm
Prototype PCB
Part No.:   ADT7481ARMZ-1R7
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Description:   Dual Channel Temperature Sensor and Overtemperature Alarm
File Size :   253 K    
Page : 20 Pages
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ADT7481
Table 1. Register Address for the Temperature Values
Temperature
Channel
Local
Remote 1
Remote 2
Register Address,
MSBs
0x00
0x01
0x30
Register Address,
LSBs
N/A
0x10 (2 MSBs)
0x33 (2 MSBs)
If Bit 3 of the Configuration 1 register is set to 1, then the
Remote 2 temperature values can be read from the following
register addresses:
Remote 2, MSBs = 0x01
Remote 2, LSBs = 0x10
The above is true only when Bit 3 of the Configuration 1
register is set. To read the Remote 1 temperatures, this bit
needs to be switched back to 0.
Only the two MSBs in the remote temperature low byte
are used. This gives the remote temperature measurement a
resolution of 0.25°C. Table 2 shows the data format for the
remote temperature low byte.
Table 2. Extended Temperature Resolution
(Remote Temperature Low Byte)
Extended Resolution
0.00°C
0.25°C
0.50°C
0.75°C
Remote Temperature Low Byte
0 000 0000
0 100 0000
1 000 0000
1 100 0000
In extended temperature mode, the upper and lower
temperatures that can be measured by the ADT7481 are
limited by the remote diode selection. While the temperature
registers can have values from
−64°C
to +191°C, most
temperature sensing diodes have a maximum temperature
range of
−55°C
to +150°C.
Note that while both local and remote temperature
measurements can be made while the part is in extended
temperature mode, the ADT7481 should not be exposed to
temperatures greater than those specified in the Absolute
section. Furthermore, the device is only guaranteed to operate
as specified at ambient temperatures from
−40°C
to +120°C.
Temperature Data Format
The ADT7481 has two temperature data formats. When
the temperature measurement range is from 0°C to +127°C
(default), the temperature data format is binary for both local
and remote temperature results. See the Temperature
Measurement Range section for information on how to
switch between the two data formats.
When the measurement range is in extended mode, an
offset binary data format is used for both local and remote
results. Temperature values in the offset binary data format
are offset by +64. Examples of temperatures in both data
formats are shown in Table 3.
Table 3. Temperature Data Format
(Local and Remote Temperature High Byte)
Temperature
−55°C
110°C
+1°C
+10°C
+25°C
+50°C
+75°C
+100°C
+125°C
+127°C
+150°C
Binary
0 000 0000
(Note 2)
0 000 0000
0 000 0001
0 000 1010
0 001 1001
0 011 0010
0 100 1011
0 110 0100
0 111 1101
0 111 1111
0 111 1111
(Note 3)
Offset Binary
(Note 1)
0 000 1001
0 100 0000
0 100 0001
0 100 1010
0 101 1001
0 111 0010
1 000 1011
1 010 0100
1 011 1101
1 011 1111
1 101 0110
When reading the full remote temperature value,
including both the high and low byte, the two registers
should be read LSB first and then the MSB. This is because
reading the LSB will cause the MSB to be locked until it is
read. This is to guarantee that the two values read are derived
from the same temperature measurement. The MSB register
updates only after it has been read. The MSB will not lock
if a SMBus repeat start is used between reading the two
registers. There needs to be a stop between reading the LSB
and MSB.
If the LSB register is read but not the MSB register, then
fail−safe protection is provided by the THERM and ALERT
signals which update with the latest temperature measurements
rather than the register values.
Temperature Measurement Range
The temperature measurement range for both local and
remote measurements is, by default, 0°C to +127°C.
However, the ADT7481 can be operated using an extended
temperature range. The temperature range in the extended
mode is
−64°C
to +191°C. The user can switch between these
two temperature ranges by setting or clearing Bit 2 in the
Configuration 1 register. A valid result is available in the next
measurement cycle after changing the temperature range.
Bit 2 Configuration Register 2 = 0 = 0°C to +127°C = default
Bit 2 Configuration Register 2 = 1 =
−64°C
to +191°C
1. Offset binary scale temperature values are offset by +64.
2. Binary scale temperature measurement returns 0 for all
temperatures <0°C.
3. Binary scale temperature measurement returns 127 for all
temperatures >127°C.
The user may switch between measurement ranges at any
time. Switching the range will also switch the data format.
The next temperature result following the switching will be
reported back to the register in the new format. However, the
contents of the limit registers will not change. It is up to the
user to ensure that when the data format changes, the limit
registers are reprogrammed as necessary. More information
on this can be found in the Limit Registers section.
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