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參數(shù)資料
| 型號： | ADT7473ARQZ-1REEL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | DIGITAL TEMP SENSOR-SERIAL, 8BIT(s), 2.50Cel, RECTANGULAR, SURFACE MOUNT |
| 封裝： | ROHS COMPLIANT, MO-137AB, QSOP-16 |
| 文件頁數(shù)： | 9/72頁 |
| 文件大?。?/td> | 1494K |
| 代理商： | ADT7473ARQZ-1REEL7 |
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ADT7473/ADT7473-1
Rev. C | Page 17 of 72
If a discrete transistor is used, the collector is not grounded and
should be linked to the base. If a PNP transistor is used, the
base is connected to the D– input and the emitter is connected
to the D+ input. If an NPN transistor is used, the emitter is
connected to the D– input and the base is connected to the D+
ADT7473/ADT7473-1 to an NPN or PNP transistor for
temperature measurement. To prevent ground noise from
interfering with the measurement, the more negative terminal
of the sensor is not referenced to ground, but is biased above
ground by an internal diode at the D– input.
2N3904
NPN
D+
D–
046
86-
0
25
ADT7473/
ADT7473-1
Figure 27. Measuring Temperature Using an NPN Transistor
2N3906
PNP
ADT7473/
ADT7473-1
D+
D–
04
68
6
-02
6
Figure 28. Measuring Temperature Using a PNP Transistor
To measure ΔVBE, the operating current through the sensor is
switched among three related currents. N1 × I and N2 × I are
different multiples of the current I, as shown in Figure 26. The
currents through the temperature diode are switched between
I and N1 × I, giving ΔVBE1, and then between I and N2 × I,
giving ΔVBE2. The temperature can then be calculated using the
two ΔVBE measurements. This method can also cancel the effect
of any series resistance on the temperature measurement.
The resulting ΔVBE waveforms are passed through a 65 kHz
low-pass filter to remove noise and then to a chopper-stabilized
amplifier. This amplifies and rectifies the waveform to produce
a dc voltage proportional to ΔVBE. The ADC digitizes this
voltage, and a temperature measurement is produced. To reduce
the effects of noise, digital filtering is performed by averaging
the results of 16 measurement cycles.
The results of remote temperature measurements are stored in
10-bit, twos complement format, as listed in Table 10. The extra
resolution for the temperature measurements is held in the
Extended Resolution Register 2 (0x77). This gives temperature
readings with a resolution of 0.25°C.
Noise Filtering
For temperature sensors operating in noisy environments,
previous practice was to place a capacitor across the D+ pin and
the D pin to help combat the effects of noise. However, large
capacitances affect the accuracy of the temperature measurement,
leading to a recommended maximum capacitor value of 1000 pF.
This capacitor reduces the noise, but does not eliminate it,
making use of the sensor difficult in a very noisy environment.
The ADT7473/ADT7473-1 has a major advantage over other
devices for eliminating the effects of noise on the external
sensor. Using the series resistance cancellation feature, a filter
can be constructed between the external temperature sensor
and the part. The effect of any filter resistance seen in series with
the remote sensor is automatically canceled from the tempera-
ture result.
The construction of a filter allows the ADT7473/ADT7473-1
and the remote temperature sensor to operate in noisy
environments. Figure 29 shows a low-pass R-C filter with the
following values:
R = 100 Ω, C = 1 nF
This filtering reduces both common-mode noise and
differential noise.
0
46
86-
0
24
D+
1nF
100
REMOTE
TEMPERATURE
SENSOR
D–
100
Figure 29. Filter Between Remote Sensor and ADT7473/ADT7473-1
SERIES RESISTANCE CANCELLATION
Parasitic resistance to the ADT7473/ADT7473-1 D+ and D
inputs (seen in series with the remote diode) is caused by a
variety of factors including PCB track resistance and track
length. This series resistance appears as a temperature offset
in the remote sensor’s temperature measurement. This error
typically causes a 0.5°C offset per Ω of parasitic resistance in
series with the remote diode.
The ADT7473/ADT7473-1 automatically cancels out the effect
of this series resistance on the temperature reading, giving a
more accurate result without the need for user characterization
of this resistance. The ADT7473/ADT7473-1 is designed to
automatically cancel up to 3 kΩ of resistance, typically. This is
transparent to the user by using an advanced temperature
measurement method. This feature allows resistances to be
added to the sensor path to produce a filter, allowing the part to
be used in noisy environments. See the Noise Filtering section
for details.
FACTORS AFFECTING DIODE ACCURACY
Remote Sensing Diode
The ADT7473/ADT7473-1 is designed to work with either
substrate transistors built into processors or discrete transistors.
Substrate transistors are generally PNP types with the collector
connected to the substrate. Discrete types can be either PNP or
NPN transistors connected as a diode (base-shorted to the
collector). If an NPN transistor is used, the collector and base
are connected to D+ and the emitter is connected to D. If a
PNP transistor is used, the collector and base are connected to
D and the emitter is connected to D+.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADT7473ARQZ-1RL | 功能描述:板上安裝溫度傳感器 FAN CNTRLR/INT MON 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 |
| ADT7473ARQZ-REEL | 功能描述:板上安裝溫度傳感器 FAN CNTRLR/INT MON 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 |
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