參數(shù)資料
型號(hào)： TMP401AIDGKTG4
廠商： Texas Instruments
文件頁(yè)數(shù)： 20/28頁(yè)
文件大?。?/td> 881K
描述： IC TEMP SENSOR DGTL OUT 8-MSOP
標(biāo)準(zhǔn)包裝： 250
功能： 溫度監(jiān)控系統(tǒng)（傳感器）
傳感器類型： 內(nèi)部和外部
感應(yīng)溫度： -40°C ~ 125°C
精確度： ±3°C 本地（最大），±5°C 遠(yuǎn)程（最大）
拓?fù)洌?/td> ADC，比較器，寄存器庫(kù)
輸出類型： 2 線 SMBus?
輸出警報(bào)： 是
輸出風(fēng)扇： 是
電源電壓： 3 V ~ 5.5 V
工作溫度： -40°C ~ 125°C
安裝類型： 表面貼裝
封裝/外殼： 8-TSSOP，8-MSOP（0.118"，3.00mm 寬）
供應(yīng)商設(shè)備封裝： 8-MSOP
包裝： 帶卷 (TR)
TMP401
SBOS371A  AUGUST 2006  REVISED OCTOBER 2007
www.ti.com
20
REMOTE SENSING
The TMP401 is designed to be used with either discrete
transistors or substrate transistors built into processor
chips and ASICs. Either NPN or PNP transistors can be
used, as long as the base-emitter junction is used as the
remote temperature sense. Either a transistor or diode
connection can also be used (see Figure 11, Basic
Connections).
Errors in remote temperature sensor readings will be the
consequence of the ideality factor and current excitation
used by the TMP401 versus the manufacturers specified
operating   current   for   a   given   transistor.   Some
manufacturers specify a high-level and low-level current
for the temperature-sensing substrate transistors. The
TMP401 uses 6礎(chǔ) for I
LOW
 and 120礎(chǔ) for I
HIGH
.
The ideality factor (? is a measured characteristic of a
remote temperature sensor diode as compared to an ideal
diode. The ideality factor for the TMP401 is trimmed to be
1.008. For transistors whose ideality factor does not match
the TMP401, Equation (1) can be used to calculate the
temperature error. Note that for the equation to be used
correctly, actual temperature (癈) must be converted to
Kelvin (癒).
T
ERR
+
h * 1.008
1.008
 
273.15 ) T(癈)
Where:
?= Ideality factor of remote temperature sensor.
T(癈) = actual temperature.
T
ERR
 = Error in TMP401 reading due to ?` 1.008.
Degree delta is the same for 癈 and 癒.
For ?= 1.004 and T(癈) = 100癈:
T
ERR
+
(
1.004*1.008
)
1.008
 
273.15)100癈
T
ERR
+ * 1.48癈
If a discrete transistor is used as the remote temperature
sensor with the TMP401, the best accuracy can be
achieved by selecting the transistor according to the
following criteria:
1.  Base-emitter voltage > 0.25V at 6礎(chǔ), at the highest
sensed temperature.
2.  Base-emitter voltage < 0.95V at 120礎(chǔ), at the
lowest sensed temperature.
3.  Base resistance < 100&.
4.  Tight control of V
BE
  characteristics indicated by
small variations in h
FE
 (that is, 50 to 150).
Based on these criteria, two recommended small-signal
transistors are the 2N3904 (NPN) or 2N3906 (PNP).
MEASUREMENT ACCURACY AND THERMAL
CONSIDERATIONS
The temperature measurement accuracy of the TMP401
depends on the remote and/or local temperature sensor
being at the same temperature as the system point being
monitored. Clearly, if the temperature sensor is not in good
thermal contact with the part of the system being
monitored, then there will be a delay in the response of the
sensor to a temperature change in the system. For remote
temperature sensing applications using a substrate
transistor (or a small, SOT23 transistor) placed close to the
device being monitored, this delay is usually not a concern.
The local temperature sensor inside the TMP401 monitors
the ambient air around the device. The thermal time
constant for the TMP401 is approximately two seconds.
This constant implies that if the ambient air changes
quickly by 100癈, it would take the TMP401 about 10
seconds (that is, five thermal time constants) to settle to
within 1癈 of the final value. In most applications, the
TMP401 package is in electrical and therefore thermal
contact with the PCB, as well as subjected to forced
airflow. The accuracy of the measured temperature
directly depends on how accurately the PCB and forced
airflow temperatures represent the temperature that the
TMP401 is measuring. Additionally, the internal power
dissipation of the TMP401 can cause the temperature to
rise above the ambient or PCB temperature. The internal
power dissipated as a result of exciting the remote
temperature sensor is negligible because of the small
currents used. For a 5.5V supply and maximum
conversion rate of eight conversions per second, the
TMP401 dissipates 1.82mW (PD
IQ
 = 5.5V x 330礎(chǔ)). If both
the ALERT
/THERM2
 and THERM
 pins are each sinking
1mA, an additional power of 0.8mW is dissipated
(PD
OUT
 = 1mA ?.4V + 1mA ?.4V = 0.8mW). Total power
dissipation is then 2.62mW (PD
IQ
 + PD
OUT
) and, with an
q
JA
 of 150癈/W, causes the junction temperature to rise
approximately 0.393癈 above the ambient.
(1)
(2)
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