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參數(shù)資料
| 型號(hào)： | ADM1021AARQ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 模擬信號(hào)調(diào)理 |
| 英文描述： | Low-Cost Microprocessor System Temperature Monitor |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO16 |
| 封裝： | MO-137AB, QSOP-16 |
| 文件頁數(shù)： | 11/12頁 |
| 文件大?。?/td> | 163K |
| 代理商： | ADM1021AARQ |
ADM1021A
–11–
REV. A
LOW POWER STANDBY MODES
The ADM1021A can be put into a low power standby mode
using hardware or software, that is, by taking the
STBY
input
low, or by setting Bit 6 of the Configuration Register. When
STBY
is high, or Bit 6 is low, the ADM1021A operates nor-
mally. When
STBY
is pulled low or Bit 6 is high, the ADC is
inhibited, so any conversion in progress is terminated without
writing the result to the corresponding value register.
The SMBus is still enabled. Power consumption in the standby
mode is reduced to less than 10
μ
A if there is no SMBus activ-
ity, or 100
μ
A if there are clock and data signals on the bus.
These two modes are similar but not identical. When
STBY
is
low, conversions are completely inhibited. When Bit 6 is set but
STBY
is high, a one-shot conversion of both channels can be initi-
ated by writing XXh to the One-Shot Register (address 0Fh).
SENSOR FAULT DETECTION
The ADM1021A has a fault detector at the D+ input that
detects if the external sensor diode is open-circuit. This is a
simple voltage comparator that trips if the voltage at D+ exceeds
V
CC
– 1 V (typical). The output of this comparator is checked
when a conversion is initiated, and sets Bit 2 of the Status Reg-
ister if a fault is detected.
If the remote sensor voltage falls below the normal measuring
range, for example due to the diode being short-circuited, the
ADC will output –128
°
C (1000 0000). Since the normal operat-
ing temperature range of the device only extends down to 0
°
C,
this output code will never be seen in normal operation, so it
can be interpreted as a fault condition.
In this respect, the ADM1021A differs from and improves upon
competitive devices that output zero if the external sensor goes
short-circuit. These devices can misinterpret a genuine 0
°
C
measurement as a fault condition.
If the external diode channel is not being used and is shorted
out, the resulting
ALERT
may be cleared by writing 80h (–128
°
C)
to the low limit register.
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY
Remote Sensing Diode
The ADM1021A is designed to work with substrate transistors
built into processors, or with discrete transistors. Substrate tran-
sistors will generally be PNP types with the collector connected
to the substrate. Discrete types can be either PNP or NPN,
connected as a diode (base shorted to collector). If an NPN
transistor is used, the collector and base are connected to D+
and the emitter to D–. If a PNP transistor is used, the collector
and base are connected to D– and the emitter to D+.
The user has no choice in the case of substrate transistors, but if
a discrete transistor is used, the best accuracy will be obtained
by choosing devices according to the following criteria:
1. Base-emitter voltage greater than 0.25 V at 6
μ
A, at the high-
est operating temperature.
2. Base-emitter voltage less than 0.95 V at 100
μ
A, at the lowest
operating temperature.
3. Base resistance less than 100
.
4. Small variation in h
FE
(say 50 to 150), which indicates tight
control of V
BE
characteristics.
Transistors such as 2N3904, 2N3906 or equivalents in SOT-23
package 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, and a number of factors
can affect this. Ideally, the sensor should be in good thermal
contact with the part of the system being measured, for example
the processor. If it is not, the thermal inertia caused by the mass
of the sensor 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, as it will be either a substrate transistor in the
processor or 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 tem-
perature around the package. The thermal time constant of the
QSOP-16 package is about 10 seconds.
In practice, the package will have electrical, and hence thermal,
connection to the printed circuit board, so the temperature rise
due to self-heating will be negligible.
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and because
the ADM1021A is measuring very small voltages from the
remote sensor, care must be taken to minimize noise induced at
the sensor inputs. The following precautions should be taken:
1. Place the ADM1021A as close as possible to the remote
sensing diode. Provided that the worst noise sources such as
clock generators, data/address buses and CRTs are avoided,
this distance can be four to eight inches.
2. Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible.
3. Use wide tracks to minimize inductance and reduce
noise pickup. 10 mil track minimum width and spacing
is recommended.
GND
D+
D
–
GND
10 mil.
10 mil.
10 mil.
10 mil.
10 mil.
10 mil.
10 mil.
Figure 17. Arrangement of Signal Tracks
4. Try to minimize the number of copper/solder joints, which
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 240
μ
V, and thermocouple voltages are
about 3
μ
V/
°
C of temperature difference. Unless there are
two thermocouples with a big temperature differential between
them, thermocouple voltages should be much less than 240
μ
V.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADM1021AARQ-REEL | 功能描述:IC SENSOR TEMP DUAL3/5.5V 16QSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 熱管理 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 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，外部傳感器 精確度:±2.5°C 本地（最大值），±5°C 遠(yuǎn)程（最大值） 拓?fù)?ADC，比較器，寄存器庫 輸出類型:2 線 SMBus? 輸出警報(bào):無 輸出風(fēng)扇:無 電源電壓:2.7 V ~ 5.5 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-8 供應(yīng)商設(shè)備封裝:SOT-23-8 包裝:Digi-Reel® 其它名稱:296-22675-6 |
| ADM1021AARQ-REEL7 | 功能描述:IC SENSOR TEMP DUAL3/5.5V 16QSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 熱管理 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 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，外部傳感器 精確度:±2.5°C 本地（最大值），±5°C 遠(yuǎn)程（最大值） 拓?fù)?ADC，比較器，寄存器庫 輸出類型:2 線 SMBus? 輸出警報(bào):無 輸出風(fēng)扇:無 電源電壓:2.7 V ~ 5.5 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-8 供應(yīng)商設(shè)備封裝:SOT-23-8 包裝:Digi-Reel® 其它名稱:296-22675-6 |
| ADM1021AARQZ | 功能描述:板上安裝溫度傳感器 PIN COMP TO ADM1021 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 |
| ADM1021AARQZ-R | 功能描述:板上安裝溫度傳感器 PIN COMP TO ADM1021 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 |
| ADM1021AARQZ-R7 | 功能描述:板上安裝溫度傳感器 PIN COMP TO ADM1021 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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