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PDF TMP04 Data sheet ( Hoja de datos )
| Número de pieza | TMP04 | |
| Descripción | Serial Digital Output Thermometers | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Serial Digital Output Thermometers
TMP03/TMP04*
FEATURES
Low Cost 3-Pin Package
Modulated Serial Digital Output
Proportional to Temperature
±1.5؇C Accuracy (typ) from –25؇C to +100؇C
Specified –40؇C to +100؇C, Operation to 150؇C
Power Consumption 6.5 mW Max at 5 V
Flexible Open-Collector Output on TMP03
CMOS/TTL Compatible Output on TMP04
Low Voltage Operation (4.5 V to 7 V)
APPLICATIONS
Isolated Sensors
Environmental Control Systems
Computer Thermal Monitoring
Thermal Protection
Industrial Process Control
Power System Monitors
GENERAL DESCRIPTION
The TMP03/TMP04 is a monolithic temperature detector that
generates a modulated serial digital output that varies in direct
proportion to the temperature of the device. An onboard sensor
generates a voltage precisely proportional to absolute temperature
which is compared to an internal voltage reference and input to a
precision digital modulator. The ratiometric encoding format of
the serial digital output is independent of the clock drift errors
common to most serial modulation techniques such as voltage-
to-frequency converters. Overall accuracy is ± 1.5°C (typical)
from –25°C to +100°C, with excellent transducer linearity. The
digital output of the TMP04 is CMOS/TTL compatible, and is
easily interfaced to the serial inputs of most popular micro-
processors. The open-collector output of the TMP03 is capable
of sinking 5 mA. The TMP03 is best suited for systems requiring
isolated circuits utilizing optocouplers or isolation transformers.
The TMP03 and TMP04 are specified for operation at supply
voltages from 4.5 V to 7 V. Operating from +5 V, supply current
(unloaded) is less than 1.3 mA.
The TMP03/TMP04 are rated for operation over the –40°C to
+100°C temperature range in the low cost TO-92, SO-8, and
TSSOP-8 surface mount packages. Operation extends to
+150°C with reduced accuracy.
(continued on page 4)
FUNCTIONAL BLOCK DIAGRAM
TMP03/04
TEMPERATURE
SENSOR
VPTAT
DIGITAL
MODULATOR
VREF
1
DOUT
2
V+
3
GND
PACKAGE TYPES AVAILABLE
TO-92
TMP03/04
12 3
DOUT
V+
GND
BOTTOM VIEW
(Not to Scale)
SO-8 and RU-8 (TSSOP)
DOUT 1
8 NC
V+ 2 TMP03/04 7 NC
GND 3 TOP VIEW 6 NC
(Not to Scale)
NC 4
5 NC
NC = NO CONNECT
*Patent pending.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1995
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
1 page  
TMP03/TMP04
Table I. Counter Size and Clock Frequency Effects on Quantization Error
Maximum
Maximum
Count Available Temp Required
4096
8192
16384
+125°C
+125°C
+125°C
Maximum
Frequency
94 kHz
188 kHz
376 kHz
Quantization
Error (+25؇C)
0.284°C
0.142°C
0.071°C
Quantization
Error (+77؇F)
0.512°F
0.256°F
0.128°F
Optimizing Counter Characteristics
Counter resolution, clock rate, and the resultant temperature
decode error that occurs using a counter scheme may be
determined from the following calculations:
1. T1 is nominally 10 ms, and compared to T2 is relatively
insensitive to temperature changes. A useful worst-case
assumption is that T1 will never exceed 12 ms over the
specified temperature range.
T1 max = 12 ms
Substituting this value for T1 in the formula, temperature
(°C) = 235 – ([T1/T2] × 400), yields a maximum value of
T2 of 44 ms at 125°C. Rearranging the formula allows the
maximum value of T2 to be calculated at any maximum
operating temperature:
T2 (Temp) = (T1max × 400)/(235 – Temp) in seconds
2. We now need to calculate the maximum clock frequency we
can apply to the gated counter so it will not overflow during
T2 time measurement. The maximum frequency is calculated
using:
Frequency (max) = Counter Size/ (T2 at maximum
temperature)
Substituting in the equation using a 12-bit counter gives,
Fmax = 4096/44 ms Ӎ 94 kHz.
3. Now we can calculate the temperature resolution, or
quantization error, provided by the counter at the chosen
clock frequency and temperature of interest. Again, using a
12-bit counter being clocked at 90 kHz (to allow for ~5%
temperature over-range), the temperature resolution at
+25°C is calculated from:
Quantization Error (°C) = 400 × ([Count1/Count2] –
[Count1 – 1]/[Count2 + 1])
Quantization Error (°F) = 720 × ([Count1/Count2] –
[Count1 – 1]/[Count2 + 1])
where, Count1 = T1max × Frequency, and Count2 =
T2 (Temp) × Frequency. At +25°C this gives a resolution of
better than 0.3°C. Note that the temperature resolution
calculated from these equations improves as temperature
increases. Higher temperature resolution will be obtained by
employing larger counters as shown in Table I. The internal
quantization error of the TMP03/TMP04 sets a theoretical
minimum resolution of approximately 0.1°C at +25°C.
Self-Heating Effects
The temperature measurement accuracy of the TMP03/TMP04
may be degraded in some applications due to self-heating.
Errors introduced are from the quiescent dissipation, and power
dissipated by the digital output. The magnitude of these
temperature errors is dependent on the thermal conductivity of
the TMP03/TMP04 package, the mounting technique, and
effects of airflow. Static dissipation in the TMP03/TMP04 is
typically 4.5 mW operating at 5 V with no load. In the TO-92
package mounted in free air, this accounts for a temperature
increase due to self-heating of
∆T = PDISS × ΘJA = 4.5 mW × 162°C/W = 0.73°C (1.3°F)
For a free-standing surface-mount TSSOP package, the
temperature increase due to self-heating would be
∆T = PDISS × ΘJA = 4.5 mW × 240°C/W = 1.08°C (1.9°F)
In addition, power is dissipated by the digital output which is
capable of sinking 800 µA continuous (TMP04). Under full
load, the output may dissipate
( )( )PDISS = 0.6 V
0.8
mA
T2
T1 + T 2
For example with T2 = 20 ms and T1 = 10 ms, the power
dissipation due to the digital output is approximately 0.32 mW
with a 0.8 mA load. In a free-standing TSSOP package this
accounts for a temperature increase due to output self-heating
of
∆T = PDISS × ΘJA = 0.32 mW × 240°C/W = 0.08°C (0.14°F)
This temperature increase adds directly to that from the
quiescent dissipation and affects the accuracy of the TMP03/
TMP04 relative to the true ambient temperature. Alternatively,
when the same package has been bonded to a large plate or
other thermal mass (effectively a large heatsink) to measure its
temperature, the total self-heating error would be reduced to
approximately
∆T = PDISS × ΘJC = (4.5 mW + 0.32 mW) × 43°C/W = 0.21°C (0.37°F)
Calibration
The TMP03 and TMP04 are laser-trimmed for accuracy and
linearity during manufacture and, in most cases, no further
adjustments are required. However, some improvement in
performance can be gained by additional system calibration. To
perform a single-point calibration at room temperature, measure
the TMP03/TMP04 output, record the actual measurement
temperature, and modify the offset constant (normally 235; see
the Output Encoding section) as follows:
Offset Constant = 235 + (TOBSERVED – TTMP03OUTPUT)
A more complicated two-point calibration is also possible. This
involves measuring the TMP03/TMP04 output at two temp-
eratures, Temp1 and Temp2, and modifying the slope constant
(normally 400) as follows:
Slope Constant =
Temp 2 − Temp1
T1
T2
@
@
Temp1
Temp1
−
T1
T2
@ Temp 2
@ Temp 2
where T1 and T2 are the output high and output low times,
respectively.
REV. 0
–5–
5 Page 
TMP03/TMP04
+5V
620Ω
V+
TMP03
DOUT
GND
VLOGIC
OPTO-COUPLER
4.7kΩ
+5V
10kΩ
V+
TMP03
4.3kΩ
DOUT
GND
a.
2N2907
270Ω
VLOGIC
OPTO-COUPLER
430Ω
b.
Figure 31. Optically Isolating the Digital Output
+5V
680Ω
+5V
V+
TMP03
DOUT
GND
H11L1
4.7kΩ
Figure 32. An Opto-Isolator with Schmitt Trigger Logic
Gate Improves Output Rise and Fall Times
The TMP03 and TMP04 are superior to analog-output
transducers for measuring temperature at remote locations,
because the digital output provides better noise immunity than
an analog signal. When measuring temperature at a remote
location, the ratio of the output pulses must be maintained. To
maintain the integrity of the pulse width, an external buffer can
be added. For example, adding a differential line driver such as
the ADM485 permits precise temperature measurements at
distances up to 4000 ft. (Figure 33). The ADM485 driver and
receiver skew is only 5 ns maximum, so the TMP04 duty cycle
is not degraded. Up to 32 ADM485s can be multiplexed onto
one line by providing additional decoding.
As previously mentioned, the digital output of the TMP03/
TMP04 provides excellent noise immunity in remote measurement
applications. The user should be aware, however, that heat from
an external cable can be conducted back to the TMP03/TMP04.
This heat conduction through the connecting wires can influence
the temperature of the TMP03/TMP04. If large temperature
differences exist within the sensor environment, an opto-
isolator, level shifter or other thermal barrier can be used to
minimize measurement errors.
+5V
2
V+
DOUT 1
TMP04
GND
3
DI
4
3
DE
8
VCC
B
7
A
6
NC 1
+5V 2
ADM485
5
Figure 33. A Differential Line Driver for Remote Tempera-
ture Measurement
Microcomputer Interfaces
The TMP03/TMP04 output is easily decoded with a micro-
computer. The microcomputer simply measures the T1 and T2
periods in software or hardware, and then calculates the temp-
erature using the equation in the Output Encoding section of
this data sheet (page 4). Since the TMP03/TMP04’s output is
ratiometric, precise control of the counting frequency is not
required. The only timing requirements are that the clock
frequency be high enough to provide the required measurement
resolution (see the Output Encoding section for details) and
that the clock source be stable. The ratiometric output of the
TMP03/TMP04 is an advantage because the microcomputer’s
crystal clock frequency is often dictated by the serial baud rate
or other timing considerations.
Pulse width timing is usually done with the microcomputer’s
on-chip timer. A typical example, using the 80C51, is shown in
Figure 34. This circuit requires only one input pin on the
microcomputer, which highlights the efficiency of the TMP04’s
pulse width output format. Traditional serial input protocols,
with data line, clock and chip select, usually require three or
more I/O pins.
+5V
V+
DOUT
TMP04
GND
INPUT
PORT 1.0
OSC
TIMER 0
(16 BITS)
80C51
MICROCOMPUTER
TIMER 1
(16 BITS)
÷ 12
TMOD REGISTER
TIMER 0 TIMER 1
TCON REGISTER
TIMER 0 TIMER 1
Figure 34. A TMP04 Interface to the 80C51 Microcomputer
The 80C51 has two 16-bit timers. The clock source for the
timers is the crystal oscillator frequency divided by 12. Thus, a
crystal frequency of 12 MHz or greater will provide resolution of
1 µs or less.
The 80C51 timers are controlled by two dedicated registers.
The TMOD register controls the timer mode of operation,
while TCON controls the start and stop times. Both the TMOD
and TCON registers must be set to start the timer.
REV. 0
–11–
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet TMP04.PDF ] | |
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