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參數(shù)資料
| 型號(hào)： | LM89 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | 【0.75∑C Accurate, Remote Diode and Local Digital Temperature Sensor with Two-Wire Interface |
| 中文描述： | 【0.75ΣC準(zhǔn)確，遠(yuǎn)程二極管和本地?cái)?shù)字溫度傳感器兩線接口 |
| 文件頁(yè)數(shù)： | 17/20頁(yè) |
| 文件大小： | 745K |
| 代理商： | LM89 |
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3.0 Applications Hints
(Continued)
optimized to measure the remote thermal diode of a 0.13
micron Pentium 4 or a Mobile Pentium 4 Processor-M pro-
cessor. A discrete diode can also be used to sense the
temperature of external objects or ambient air. Remember
that a discrete diode’s temperature will be affected, and often
dominated, by the temperature of its leads.
Most silicon diodes do not lend themselves well to this
application. It is recommended that a 2N3904 transistor
base emitter junction be used with the collector tied to the
base.
An LM89 with a diode-connected 2N3904 approximates the
temperature reading of the LM89 with a Pentium 4 micropro-
cessor less 1C. T
2N3904
= T
P4
1C
3.1 DIODE NON-IDEALITY
3.1.1 Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following
relationship holds for variables V
BE
, T and I
f
:
where:
q = 1.6x10
19
Coulombs (the electron charge),
T = Absolute Temperature in Kelvin
k = 1.38x10
23
joules/K (Boltzmann’s constant),
η
is the non-ideality factor of the process the diode is
manufactured on,
I
S
= Saturation Current and is process dependent,
I
f
= Forward Current through the base emitter junction
V
BE
= Base Emitter Voltage drop
In the active region, the -1 term is negligible and may be
eliminated, yielding the following equation
In the above equation,
η
and I
are dependant upon the
process that was used in the fabrication of the particular
diode. By forcing two currents with a very controlled ratio (N)
and measuring the resulting voltage difference, it is possible
to eliminate the I
S
term. Solving for the forward voltage
difference yields the relationship:
The voltage seen by the LM89 also includes the I
R
voltage
drop of the series resistance. The non-ideality factor,
η
, is
the only other parameter not accounted for and depends on
the diode that is used for measurement. Since
V
is
proportional to both
η
and T, the variations in
η
cannot be
distinguished from variations in temperature. Since the non-
ideality factor is not controlled by the temperature sensor, it
will directly add to the inaccuracy of the sensor. For the
Pentium 4 and Mobile Pentium Processor-M Intel specifies a
±
0.1% variation in
η
from part to part. As an example,
assume a temperature sensor has an accuracy specification
of
±
1C at room temperature of 25 C and the process used
to manufacture the diode has a non-ideality variation of
±
0.1%. The resulting accuracy of the temperature sensor at
room temperature will be:
T
ACC
=
±
1C + (
±
0.1% of 298 K) =
±
1.4 C
The additional inaccuracy in the temperature measurement
caused by
η
, can be eliminated if each temperature sensor is
calibrated with the remote diode that it will be paired with.
Processor Family
η
, non-ideality
typ
1.0065
1.0057
1.008
min
1
max
1.0125
1.0125
Pentium III CPUID 67h
Pentium III CPUID
68h/PGA370Socket/Celeron
Pentium 4, 423 pin
Pentium 4, 478 pin
0.13 micron, Pentium 4
MMBT3904
AMD Athlon MP model 6
0.9933
0.9933
1.0011
1.0045
1.0045
1.0021
1.003
1.008
1.0368
1.0368
1.0030
1.002
1.016
3.1.2 Compensating for Diode Non-Ideality
In order to compensate for the errors introduced by non-
ideality, the temperature sensor is calibrated for a particular
processor. National Semiconductor temperature sensors are
always calibrated to the typical non-ideality of a given pro-
cessor type. The LM89 is calibrated for the non-ideality of a
0.13 micron, Mobile Pentium 4, 1.0021. When a temperature
sensor calibrated for a particular processor type is used with
a different processor type or a given processor type has a
non-ideality that strays from the typical, errors are intro-
duced.
Temperature errors associated with non-ideality may be re-
duced in a specific temperature range of concern through
use of the offset registers (11h and 12h).
Please send an email to hardware.monitor.team
@
nsc.com
requesting further information on our recommended setting
of the offset register for different processor types.
L
www.national.com
17
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