ADM1026JST-REEL7 View Datasheet(PDF) - ON Semiconductor
Part Name
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Manufacturer
ADM1026JST-REEL7 Datasheet PDF : 55 Pages
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ADM1026
The results of external temperature measurements are
stored in 8−bit, twos complement format, as illustrated in
Table 4.
Table 4. Temperature Data Format
Temperature
Digital Output
Hex
−128°C
−125°C
−100°C
−75°C
−50°C
−25°C
−10°C
0°C
10°C
25°C
50°C
75°C
100°C
125°C
127°C
1000 0000
80
1000 0011
83
1001 1100
9C
1011 0101
B5
1100 1110
CE
1110 0111
E7
1111 0110
F6
0000 0000
00
0000 1010
0A
0001 1001
19
0011 0010
32
0100 1011
4B
0110 0100
64
0111 1101
7D
0111 1111
7F
Layout Considerations
Digital boards can be electrically noisy environments.
Take these precautions to protect the analog inputs from
noise, particularly when measuring the very small voltages
from a remote diode sensor.
• Place the ADM1026 as close as possible to the remote
sensing diode. Provided that the worst noise sources
such as clock generators, data/address buses, and CRTs
are avoided, this distance can be 4 to 8 inches.
• Route the D+ and D− tracks close together, in parallel,
with grounded guard tracks on each side. Provide a
ground plane under the tracks if possible.
• Use wide tracks to minimize inductance and reduce noise
pickup. A 10 mil track minimum width and spacing is
recommended.
GND
D+
D–
GND
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
Figure 34. Arrangement of Signal Tracks
• Try to minimize the number of copper/solder joints,
which can cause thermocouple effects. Where copper/
solder joints are used, make sure that they are in both
the D+ and D− paths and are at the same temperature.
• Thermocouple effects should not be a major problem
because 1°C corresponds to about 240 mV, and
thermocouple voltages are about 3 mV/°C of temperature
difference. Unless there are two thermocouples with a
big temperature differential between them, thermocouple
voltages should be much less than 200 mV.
• Place a 0.1 mF bypass capacitor close to the ADM1026.
• If the distance to the remote sensor is more than eight
inches, the use of twisted−pair cable is recommended.
This works from about 6 to 12 feet.
• For very long distances (up to 100 feet), use shielded
twisted pair such as Belden #8451 microphone cable.
Connect the twisted pair to D+ and D− and the shield to
GND close to the ADM1026. Leave the remote end of
the shield unconnected to avoid ground loops.
Because the measurement technique uses switched
current sources, excessive cable and/or filter capacitance
can affect the measurement. When using long cables, the
filter capacitor may be reduced or removed. Cable resistance
can also introduce errors. A 1 W series resistance introduces
about 0.5°C error.
Limit Values
Limit values for analog measurements are stored in the
appropriate limit registers. In the case of voltage
measurements, high and low limits can be stored so that an
interrupt request is generated if the measured value goes
above or below acceptable values. In the case of
temperature, a hot temperature or high limit can be
programmed, and a hot temperature hysteresis or low limit
can be programmed, which is usually some degrees lower.
This can be useful because it allows the system to be shut
down when the hot limit is exceeded, and restarted
automatically when it has cooled down to a safe
temperature.
Analog Monitoring Cycle Time
The analog monitoring cycle begins when a 1 is written to
the start bit (Bit 0), and a 0 to the INT_Clear bit (Bit 2) of the
configuration register. INT_Enable (Bit 1) should be set to
1 to enable the INT output. The ADC measures each analog
input in turn, starting with Remote Temperature Channel 1
and ending with local temperature. As each measurement is
completed, the result is automatically stored in the
appropriate value register. This round−robin monitoring
cycle continues until it is disabled by writing a 0 to Bit 0 of
the configuration register. Because the ADC is typically left
to free−run in this way, the most recently measured value of
any input can be read out at any time.
For applications where the monitoring cycle time is
important, it can easily be calculated.
The total number of channels measured is:
• Five dedicated supply voltage inputs
• Ten general−purpose analog inputs
• 3.3 V MAIN
• 3.3 V STBY
• Local temperature
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