參數(shù)資料
型號(hào): ADT7466ARQZ-REEL7
廠商: ANALOG DEVICES INC
元件分類: 模擬信號(hào)調(diào)理
英文描述: dBCool Remote Thermal Controller and Voltage Monitor
中文描述: SPECIALTY ANALOG CIRCUIT, PDSO16
封裝: LEAD FREE, MO-137AB, QSOP-16
文件頁(yè)數(shù): 20/48頁(yè)
文件大?。?/td> 1269K
代理商: ADT7466ARQZ-REEL7
ADT7466
Thermistor Linearization
A linear transfer function can be obtained over a limited
temperature range by connecting the thermistor in series with
an optimum resistor. Placing a resistor in series with the
thermistor as shown in Figure 26 produces an S-shaped error
curve as shown in Figure 27. The overall error across the range
can be reduced by calculating the external resistor so that the
error is 0 at the ends of the range. R
EXT
is calculated as follows:
Rev. 0 | Page 20 of 48
)
2
(
)
2
)
(
MID
MAX
MIN
MAX
MIN
MAX
R
MIN
R
MID
EXT
R
R
R
R
R
R
R
×
+
×
×
+
×
=
where:
R
MIN
is the thermistor value at T
MIN
.
R
MAX
is the thermistor value at T
MAX
.
R
MID
is the thermistor value at
2
MAX
T
MIN
T
+
Figure 27 shows the linearity error using a 100 k thermistor
with a B value of 3500 and a 14400 resistor. Using the
specified thermistor and resistor, the error over a temperature
range of 30°C to 100°C is less than ±2°C. Other thermistors can
be used, but the resistor value is different. A smaller error can
be achieved over a narrower temperature range; conversely, a
wider temperature range can be used, but the error is greater. In
both cases, the optimum resistor value is different.
2
1
0
–1
–2
30
40
50
60
70
80
90
100
0
TEMPERATURE (
°
C)
E
°
C
Figure 27. Linearity Error Using Specified Components
Thermistor Normalization
Even when the thermistor is linearized, it does not provide an
output to the ADC that gives a direct temperature reading in
degrees Celsius. The linearized data is proportional to the
voltage applied; however, normalization is needed to use the
value as a temperature reading.
To overcome this problem, when an analog input is configured
for use with a thermistor, the output of the ADC is scaled and
offset so that it produces the same output (for example, 1 LSB =
0.25°C) as from the thermal diode input, when R
EXT
is chosen to
linearize the thermistor over 30°C to 100°C.
Normalization can be chosen for 10 k thermistors by setting
Bit 0 of Configuration Register 2 (0x01) or for 100 k
thermistors by clearing this bit (default setting).
READING TEMPERATURE FROM THE ADT7466
It is important to note that temperature can be read from the
ADT7466 as an 8-bit value (with 1°C resolution) or as a 10-bit
value (with 0.25°C resolution). If only 1°C resolution is
required, the temperature readings can be read at any time
and in no particular order.
If the 10-bit measurement is required, this involves a 2-register
read for each measurement. The extended resolution registers
(0x08 and 0x09) should be read first. This causes all temperature
reading registers to be frozen until all temperature reading
registers have been read. This prevents an MSB reading from
being updated while its 2 LSBs are being read and vice versa.
Measurement Sequence
The ADT7466 automatically measures each analog and
temperature channel in the following round-robin sequence:
1.
AIN1/TH1
2.
AIN2(TH2)
3.
V
CC
4.
Remote Temperature 1 (D1)
5.
Local Temperature
If AIN1 and AIN2 are configured for a second thermal diode,
this is measured instead of the AIN1 and AIN 2 measurements,
and the result stored in the AIN1 reading register (0x0A).
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