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參數資料
| 型號： | ADT7461ARM |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 模擬信號調理 |
| 英文描述： | 【1∑C Temperature Monitor with Series Resistance Cancellation |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PDSO8 |
| 封裝： | MO-187-AA, MSOP-8 |
| 文件頁數： | 9/24頁 |
| 文件大小： | 854K |
| 代理商： | ADT7461ARM |
ADT7461
FUNCTIONAL DESCRIPTION
The ADT7461 is a local and remote temperature sensor and
over/under temperature alarm, with the added ability to
automatically cancel the effect of 3 k (typical) of resistance
in series with the temperature monitoring diode. When the
ADT7461 is operating normally, the on-board ADC operates in
a free-running mode. The analog input multiplexer alternately
selects either the on-chip temperature sensor to measure its
local temperature or the remote temperature sensor. The ADC
digitizes these signals and the results are stored in the local and
remote temperature value registers.
The local and remote measurement results are compared with
the corresponding high, low, and THERM temperature limits,
stored in eight on-chip registers. Out-of-limit comparisons gen-
erate flags that are stored in the status register. A result that
exceeds the high temperature limit, the low temperature limit,
or an external diode fault will cause the ALERT output to assert
low. Exceeding THERM temperature limits causes the THERM
output to assert low. The ALERT output can be reprogrammed
as a second THERM output.
The limit registers can be programmed, and the device con-
trolled and configured, via the serial SMBus. The contents of
any register can also be read back via the SMBus.
Control and configuration functions consist of: switching the
device between normal operation and standby mode, selecting
the temperature measurement scale, masking or enabling the
ALERT output, switching Pin 6 between ALERT and THERM2,
and selecting the conversion rate.
SERIES RESISTANCE CANCELLATION
Parasitic resistance, seen in series with the remote diode, to the
D+ and D inputs to the ADT7461, 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 ohm of parasitic resistance in series with the
remote diode.
The ADT7461 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 resis-
tance. The ADT7461 is designed to automatically cancel typically
up to 3 k of resistance. By using an advanced temperature
measurement method, this is transparent to the user. This fea-
ture allows resistances to be added to the sensor path to produce
a filter, allowing the part to be used in noisy environments. See
the section on
for more details.
Noise Filtering
Noise Filtering
more information on C1.
TEMPERATURE MEASUREMENT METHOD
A simple method of measuring temperature is to exploit the
negative temperature coefficient of a diode, measuring the
base-emitter voltage (V
BE
) of a transistor, operated at constant
current. Unfortunately, this technique requires calibration to
null out the effect of the absolute value of V
BE
, which varies
from device to device.
The technique used in the ADT7461 is to measure the change
in V
BE
when the device is operated at three different currents.
Previous devices have used only two operating currents, but it is
the use of a third current that allows automatic cancellation of
resistances in series with the external temperature sensor.
Figure 14 shows the input signal conditioning used to measure
the output of an external temperature sensor. This figure shows
the external sensor as a substrate transistor, but it could equally
be a discrete transistor. If a discrete transistor is used, the collec-
tor will not be grounded and should be linked to the base. To
prevent ground noise 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. C1 may optionally be added as a noise filter (recom-
mended maximum value 1000 pF). However, a better option in
noisy environments is to add a filter, as described in the section
on
. See the section on
for
Layout Considerations
To measure V
BE
, the operating current through the sensor is
switched among three related currents. Shown in Figure 14,
N1 × I and N2 × I are different multiples of the current I. The
currents through the temperature diode are switched between I
and N1 × I, giving V
BE1
, and then between I and N2 × I, giving
V
BE2
. The temperature may then be calculated using the two
V
BE
measurements. This method can also be shown to cancel
the effect of any series resistance on the temperature measurement.
The resulting V
BE
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 V
BE
. The ADC digitizes this volt-
age and a temperature measurement is produced. To reduce the
effects of noise, digital filtering is performed by averaging the
results of 16 measurement cycles for low conversion rates. At
rates of 16, 32, and 64 conversions/second, no digital averaging
takes place.
Signal conditioning and measurement of the internal tempera-
ture sensor is performed in the same manner.
Rev. 0 | Page 9 of 24
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| ADT7461ARMZ | 功能描述:板上安裝溫度傳感器 EXT TMP RGE IC 1C TDM SRC RoHS:否 制造商:Omron Electronics 輸出類型:Digital 配置: 準確性:+/- 1.5 C, +/- 3 C 溫度閾值: 數字輸出 - 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 關閉: 安裝風格: 封裝 / 箱體: 設備功能:Temperature and Humidity Sensor |
| ADT7461ARMZ | 制造商:ON Semiconductor 功能描述:Temperature Sensor IC |
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