factor n
NOMINAL
is used to measure the temperature of
a diode with a different ideality factor n1. The measured
temperature T
M
can be corrected using:
where temperature is measured in Kelvin and
n
NOMIMAL
for the MAX6689 is 1.012. As an example,
assume you want to use the MAX6689 with a CPU that
has an ideality factor of 1.002. If the diode has no
series resistance, the measured data is related to the
real temperature as follows:
For a real temperature of +85癈 (358.15K), the mea-
sured temperature is +81.46癈 (354.61K), an error of
-3.539癈.
Series Resistance Cancellation
Some thermal diodes on high-power ICs can have
excessive series resistance, which can cause tempera-
ture measurement errors with conventional remote tem-
perature sensors. Channel 1 of the MAX6689 has a
series resistance cancellation feature (enabled by bit 3
of the configuration 1 register) that eliminates the effect
of diode series resistance. Set bit 3 to 1 if the series
resistance is large enough to affect the accuracy of
channel 1. The series resistance cancellation function
increases the conversion time for channel 1 by 125ms.
This feature cancels the bulk resistance of the sensor
and any other resistance in series (wire, contact resis-
tance, etc.). The cancellation range is from 0 to 100?
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor,
its collector and base must be connected together.
Table 10 lists examples of discrete transistors that are
appropriate for use with the MAX6689. The transistor
must be a small-signal type with a relatively high for-
ward voltage; otherwise, the A/D input voltage range
can be violated. The forward voltage at the highest
expected temperature must be greater than 0.25V at
10礎(chǔ), and at the lowest expected temperature, the for-
ward voltage must be less than 0.95V at 100礎(chǔ). Large
power transistors must not be used. Also, ensure that
the base resistance is less than 100? Tight specifica-
tions for forward current gain (50 < ?<150, for exam-
ple) indicate that the manufacturer has good process
controls and that the devices have consistent V
BE
char-
acteristics. Manufacturers of discrete transistors do not
normally specify or guarantee ideality factor. This is
normally not a problem since good-quality discrete
transistors tend to have ideality factors that fall within a
relatively narrow range. We have observed variations in
remote temperature readings of less than ?癈 with a
variety of discrete transistors. Still, it is good design
practice to verify good consistency of temperature
readings with several discrete transistors from any
manufacturer under consideration.
T
T
n
n
T
T
ACTUAL    M
NOMINAL
M
M
=
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=
1
1 012
1 002
1 00998
.
.
( .
)
T   T
n
n
M
ACTUAL
NOMINAL
=
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
1
7-Channel Precision Temperature Monitor
______________________________________________________________________________________   13
Table 6. Configuration 3 Register
BIT
NAME
POR
STATE
FUNCTION
7 (MSB)
Reserved
0
6
Reserved
0
5
Mask OVERT 6
0
Channel 6 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 6
OVERT.
4
Mask OVERT 5
0
Channel 5 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 5
OVERT.
3
Mask OVERT 4
0
Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4
OVERT.
2
Reserved
0
1
Reserved
0
0
Mask OVERT 1
0
Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1
OVERT.
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
MAX6689UP34+ |
功能描述:板上安裝溫度傳感器 7Ch Precision Temperature Monitor 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 |
MAX6689UP34+T |
功能描述:板上安裝溫度傳感器 7Ch Precision Temperature Monitor 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 |
MAX6689UP34-T |
制造商:Maxim Integrated Products 功能描述:7-CHANNEL PRECISION TEMPERATURE MONITOR - Tape and Reel |
MAX6689UP38 |
制造商:Maxim Integrated Products 功能描述:7-CHANNEL PRECISION TEMPERATURE MONITOR - Rail/Tube |
MAX6689UP38-T |
制造商:Maxim Integrated Products 功能描述:7-CHANNEL PRECISION TEMPERATURE MONITOR - Tape and Reel |