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參數(shù)資料
| 型號： | ASC7511M8 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | LOW- OLTAGE 2-WIRE DIGITAL TEMPERATURE SENSOR |
| 中文描述： | 低OLTAGE 2 - Wire數(shù)字溫度傳感器 |
| 文件頁數(shù)： | 14/19頁 |
| 文件大小： | 273K |
| 代理商： | ASC7511M8 |
- 14 -
Andigilog, Inc. 2006
www.andigilog.com
August 2006 - 70A04010
aSC7511
range of non-ideality. The trend with CPUs is for a lower
value with a larger spread.
When thermal diode has a non-ideality factor other than
1.008 the difference in temperature reading at a particular
temperature may be interpreted with the following
equation:
=
actual
n
reported
T
actual
T
008
.
where:
T
reported
T
n
Temperatures are in Kelvins or °C + 273.15.
= reported temperature in temperature register.
actual
= actual remote diode temperature.
= selected diode’s non-ideality factor,
actual
.
nf
The temperature error caused by non-ideality difference
is directly proportional to the difference from 1.008, but a
small difference in non-ideality results in a relatively large
difference in temperature reading. For example, if there
were a ±1% tolerance in the non-Ideality of a diode it
would result in a ±2.7 degree difference (at 0°C) in the
result (0.01 x 273.15).
This difference varies with temperature such that a fixed
offset value may only be used over a very narrow range.
Typical correction method required when measuring a
wide range of temperature values is to scale the
temperature reading in the host firmware.
Part
nf
Min
nf
Nom
nf
Max
Pentium III (CPUID 68h)
Pentium 4, 130nM
Pentium 4, 90nM
Intel Pentium M
AMD Athlon
Model 6
AMD Duron
Models 7 and 8
AMD Athlon
Models 8 and 10
2N3904
1.0057
1.001
1.0015
1.008
1.002
1.011
1.0022
1.0125
1.003
1.0029
1.002
1.008
1.016
1.002
1.008
1.016
1.0000
1.0037
1.0090
1.003
1.0043
1.005
Table 8. Representative CPU Thermal Diode
and Transistor Non-Ideality Factors
CPU or ASIC Substrate Remote Diodes
A substrate diode is a parasitic PNP transistor that has its
collector tied to ground through the substrate and the
base (D-) and emitter (D+) brought out to pins.
Connection to these pins is shown in Figure 13. The non-
ideality figures in Table 8 include the effects of any
package resistance and represent the value seen from
the CPU socket. The temperature indicated will need to
be compensated for the departure from a non-ideality of
1.008.
Figure 9. CPU Remote Diode Connection
Series Resistance
Any resistance in the connections from the aSC7511 to
the CPU pins should be accounted for in interpreting the
results of a measurement.
The impact of series resistance on the measured
temperature is a result of measurement currents
developing offset voltages that add to the diode voltage.
This is relatively constant with temperature and may be
corrected with a fixed value in the offset register. To
determine the temperature impact of resistance is as
follows:
Δ
T
R
=
R
S
×
T
V
× Δ
I
D
or,
Δ
T
R
=
R
S
×
90
μ
A
230
μ
V /
°
C
=
R
S
×
0.391
°
C /
Ω
where:
Δ
T
R
= difference in the temperature reading from actual.
R
= total series resistance of interconnect (both leads).
Δ
I
D
= difference in the two diode current levels (90μA).
T
= scale of temperature vs. V
BE
(230μV/°C).
S
V
For example, a total series resistance of 10
would give
an offset of +3.9°C.
Discrete Remote Diodes
When sensing temperatures other than the CPU or GPU
substrate, an NPN or PNP transistor may be used. Most
commonly used are the 2N3904 and 2N3906. These
have characteristics similar to the CPU substrate diode
with non-ideality around 1.003. They are connected with
base to collector shorted as shown in Figure 14.
While it is important to minimize the distance to the
remote diode to reduce high-frequency noise pickup, they
may be located many feet away with proper shielding.
Shielded, twisted-pair cable is recommended, with the
shield connected only at the aSC7511 end as close as
possible to the ground pin of the device.
As with the CPU substrate diode, the temperature
reported will be subject to the same errors due to non-
D+
D-
CPU
aSC7511
Substrate
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