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參數(shù)資料
| 型號(hào)： | ADT7461AR-REEL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 模擬信號(hào)調(diào)理 |
| 英文描述： | 【1∑C Temperature Monitor with Series Resistance Cancellation |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO8 |
| 封裝： | MS-012-AA, SOIC-8 |
| 文件頁數(shù)： | 19/24頁 |
| 文件大?。?/td> | 854K |
| 代理商： | ADT7461AR-REEL7 |
ADT7461
If a discrete transistor is being used with the ADT7461, the best
accuracy will be obtained by choosing devices according to the
following criteria:
Base-emitter voltage greater than 0.25 V at 6 μA, at the
highest operating temperature.
Base-emitter voltage less than 0.95 V at 100 μA, at the
lowest operating temperature.
Base resistance less than 100 .
Small variation in h
FE
(say 50 to 150) that indicates tight
control of V
BE
characteristics.
Transistors, such as 2N3904, 2N3906, or equivalents in SOT-23
packages, are suitable devices to use.
THERMAL INERTIA AND SELF-HEATING
Accuracy depends on the temperature of the remote sensing
diode and/or the internal temperature sensor being at the same
temperature as that being measured. A number of factors can
affect this. Ideally, the sensor should be in good thermal contact
with the part of the system being measured. If it is not, the
thermal inertia caused by the sensor’s mass will cause a lag in
the response of the sensor to a temperature change. In the case
of the remote sensor, this should not be a problem, since it will
either be a substrate transistor in the processor or can be a small
package device, such as SOT-23, placed in close proximity to it.
The on-chip sensor, however, will often be remote from the
processor and will only be monitoring the general ambient
temperature around the package. The thermal time constant of
the SOIC-8 package in still air is about 140 seconds, and if the
ambient air temperature quickly changed by 100 degrees, it
would take about 12 minutes (5 time constants) for the junction
temperature of the ADT7461 to settle within 1 degree of this. In
practice, the ADT7461 package will be in electrical, and hence
thermal, contact with a PCB and may also be in a forced airflow.
How accurately the temperature of the board and/or the forced
airflow reflects the temperature to be measured will also affect
the accuracy. Self-heating due to the power dissipated in the
ADT7461 or the remote sensor causes the chip temperature of
the device or remote sensor to rise above ambient. However, the
current forced through the remote sensor is so small that self-
heating is negligible. In the case of the ADT7461, the worst-case
condition occurs when the device is converting at 64 conver-
sions per second while sinking the maximum current of 1 mA
at the ALERT and THERM output. In this case, the total power
dissipation in the device is about 4.5 mW. The thermal resis-
tance, θ
JA
, of the SOIC-8 package is about 121°C/W.
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the
ADT7461 is measuring very small voltages from the remote
sensor, so care must be taken to minimize noise induced at the
sensor inputs. The following precautions should be taken:
Place the ADT7461 as close as possible to the remote sens-
ing diode. Provided that the worst noise sources, i.e., clock
generators, data/address buses, and CRTs, are avoided, this
distance can be 4 inches to 8 inches.
Route the D+ and D– tracks close together, in parallel,
with grounded guard tracks on each side. To minimize
inductance and reduce noise pick-up, a 5 mil track width
and spacing is recommended. Provide a ground plane
under the tracks if possible.
0
5MIL
5MIL
5MIL
5MIL
5MIL
5MIL
5MIL
GND
D+
D–
GND
Figure 22. Typical Arrangement of Signal Tracks
Try to minimize the number of copper/solder joints
that can cause thermocouple effects. Where copper/solder
joints are used, make sure that they are in both the D+ and
D path and at the same temperature.
Thermocouple effects should not be a major problem as
1°C corresponds to about 200 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 μF bypass capacitor close to the V
DD
pin. In
extremely noisy environments, an input filter capacitor
may be placed across D+ and D close to the ADT7461.
This capacitance can effect the temperature measurement,
so care must be taken to ensure that any capacitance seen
at D+ and D is a maximum of 1,000 pF. This maximum
value includes the filter capacitance, plus any cable or stray
capacitance between the pins and the sensor diode.
If the distance to the remote sensor is more than 8 inches,
the use of twisted pair cable is recommended. This will
work up to about 6 feet to 12 feet.
Rev. 0 | Page 19 of 24
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADT7461ARZ | 功能描述:板上安裝溫度傳感器 1C TDM EX TMP RGE IC RoHS:否 制造商:Omron Electronics 輸出類型:Digital 配置: 準(zhǔn)確性:+/- 1.5 C, +/- 3 C 溫度閾值: 數(shù)字輸出 - 總線接口:2-Wire, I2C, SMBus 電源電壓-最大:5.5 V 電源電壓-最小:4.5 V 最大工作溫度:+ 50 C 最小工作溫度:0 C 關(guān)閉: 安裝風(fēng)格: 封裝 / 箱體: 設(shè)備功能:Temperature and Humidity Sensor |
| ADT7461ARZ | 制造商:ON Semiconductor 功能描述:TEMPERATURE SENSOR IC |
| ADT7461ARZ-REEL | 功能描述:板上安裝溫度傳感器 1C TDM TMP RNG IC RoHS:否 制造商:Omron Electronics 輸出類型:Digital 配置: 準(zhǔn)確性:+/- 1.5 C, +/- 3 C 溫度閾值: 數(shù)字輸出 - 總線接口:2-Wire, I2C, SMBus 電源電壓-最大:5.5 V 電源電壓-最小:4.5 V 最大工作溫度:+ 50 C 最小工作溫度:0 C 關(guān)閉: 安裝風(fēng)格: 封裝 / 箱體: 設(shè)備功能:Temperature and Humidity Sensor |
| ADT7461ARZ-REEL7 | 功能描述:板上安裝溫度傳感器 1C TDM TMP RNG IC RoHS:否 制造商:Omron Electronics 輸出類型:Digital 配置: 準(zhǔn)確性:+/- 1.5 C, +/- 3 C 溫度閾值: 數(shù)字輸出 - 總線接口:2-Wire, I2C, SMBus 電源電壓-最大:5.5 V 電源電壓-最小:4.5 V 最大工作溫度:+ 50 C 最小工作溫度:0 C 關(guān)閉: 安裝風(fēng)格: 封裝 / 箱體: 設(shè)備功能:Temperature and Humidity Sensor |
| ADT7462 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Flexible Temperature and Voltage Monitor and System Fan Controller |
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