ADM1026JST ON Semiconductor, ADM1026JST Datasheet - Page 20

• Manufacturer Part Number: ADM1026JST
• Description: IC CNTRL SYS REF/EEPROM 48LQFP
• Manufacturer: ON Semiconductor

Specifications of ADM1026JST

• Rohs Status: RoHS non-compliant
• Function: Hardware Monitor
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 100°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 48-LFQFP

stored in 8−bit, twos complement format, as illustrated in
Table 4.
Layout Considerations
Take these precautions to protect the analog inputs from
noise, particularly when measuring the very small voltages
from a remote diode sensor.
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Table 4. Temperature Data Format
The results of external temperature measurements are
Digital boards can be electrically noisy environments.
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.
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
Temperature
GND
GND
D+
D–
−128°C
−125°C
−100°C
−75°C
−50°C
−25°C
−10°C
100°C
125°C
127°C
Figure 34. Arrangement of Signal Tracks
10°C
25°C
50°C
75°C
0°C
Digital Output
1000 0000
1000 0011
1001 1100
1011 0101
0000 0000
0000 1010
0001 1001
0011 0010
0100 1011
0110 0100
1100 1110
0111 1101
1110 0111
1111 0110
0111 1111
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
10MIL
Hex
9C
CE
7D
B5
E7
F6
0A
4B
7F
80
83
00
19
32
64
http://onsemi.com
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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
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 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.
important, it can easily be calculated.
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Because the measurement technique uses switched
Limit values for analog measurements are stored in the
The analog monitoring cycle begins when a 1 is written to
For applications where the monitoring cycle time is
The total number of channels measured is:
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.
Five dedicated supply voltage inputs
Ten general−purpose analog inputs
3.3 V MAIN
3.3 V STBY
Local temperature