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PDF TMP12 Data sheet ( Hoja de datos )

Número de pieza TMP12
Descripción Airflow and Temperature Sensor
Fabricantes Analog Devices 
Logotipo Analog Devices Logotipo



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a
Airflow and Temperature Sensor
FEATURES
Temperature Sensor Includes 100 Heater
Heater Provides Power IC Emulation
Accuracy ؎3°C typ. from ؊40°C to ؉100°C
Operation to ؉150°C
5 mV/°C Internal Scale-Factor
Resistor Programmable Temperature Setpoints
20 mA Open-Collector Setpoint Outputs
Programmable Thermal Hysteresis
Internal 2.5 V Reference
Single 5 V Operation
400 µA Quiescent Current (Heater OFF)
Minimal External Components
APPLICATIONS
System Airflow Sensor
Equipment Over-Temperature Sensor
Over-Temperature Protection
Power Supply Thermal Sensor
Low-Cost Fan Controller
GENERAL DESCRIPTION
The TMP12 is a silicon-based airflow and temperature sensor
designed to be placed in the same airstream as heat generating
components that require cooling. Fan cooling may be required
continuously, or during peak power demands, e.g. for a power
supply, and if the cooling systems fails, system reliability and/or
safety may be impaired. By monitoring temperature while emu-
lating a power IC, the TMP12 can provide a warning of cooling
system failure.
The TMP12 generates an internal voltage that is linearly pro-
portional to Celsius (Centigrade) temperature, nominally
؉5 mV/°C. The linearized output is compared with voltages
from an external resistive divider connected to the TMP12’s
2.5 V precision reference. The divider sets up one or two refer-
ence voltages, as required by the user, providing one or two
temperature setpoints. Comparator outputs are open-collector
transistors able to sink over 20 mA. There is an on-board hys-
teresis generator provided to speed up the temperature-setpoint
output transitions, this also reduces erratic output transitions in
noisy environments. Hysteresis is programmed by the external
resistor chain and is determined by the total current drawn from
the 2.5 V reference. The TMP12 airflow sensor also incorpo-
rates a precision, low temperature coefficient 100 heater
resistor that may be connected directly to an external 5 V sup-
ply. When the heater is activated it raises the die temperature in
TMP12*
FUNCTIONAL BLOCK DIAGRAM
VREF
SET
HIGH
SET
LOW
GND
HYSTERESIS
CURRENT
CURRENT
MIRROR
IHYS
WINDOW
COMPARATOR
VOLTAGE
REFERENCE
AND
SENSOR
1k
-
+
+
-
HYSTERESIS
VOLTAGE
100
V+
OVER
UNDER
HEATER
PINOUTS
DIP And SO
VREF 1
8 V+
SET HIGH 2
SET LOW 3
TOP VIEW
(Not to Scale)
7 OVER
6 UNDER
GND 4
5 HEATER
the DIP package approximately 20°C above ambient (in still
air). The purpose of the heater in the TMP12 is to emulate a
power IC, such as a regulator or Pentium CPU which has a high
internal dissipation.
When subjected to a fast airflow, the package and die tempera-
tures of the power device and the TMP12 (if located in the
same airstream) will be reduced by an amount proportional to
the rate of airflow. The internal temperature rise of the TMP12
may be reduced by placing a resistor in series with the heater, or
reducing the heater voltage.
The TMP12 is intended for single 5 V supply operation, but will
operate on a 12 V supply. The heater is designed to operate from
5 V only. Specified temperature range is from ؊40°C to ؉125°C,
operation extends to ؉150°C at 5 V with reduced accuracy.
The TMP12 is available in 8-pin plastic DIP and SO packages.
*Protected by U.S. Patent No. 5,195,827.
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




TMP12 pdf
TMP12
35
V = 5V
SO–8 SOLDERED TO .5 " .3" Cu PCB
30
a
25
b
a. 0 FPM
20
b. 250 FPM
c. 450 FPM
15
d. 600 FPM
10
5
c
d
AIR FLOW RATES
0
0 50 100 150 200 250
HEATER RESISTOR POWER DISSIPATION – mW
Figure 1. SOIC Junction Temperature Rise vs. Heater
Dissipation
25
V = 5V
PDIP SOLDERED TO 2" 1.31" Cu PCB
c
b
20 a
a. 0 FPM
b. 250 FPM
15
c. 450 FPM
d. 600 FPM
10
d
5 AIR FLOW RATES
0
0 50 100 150 200 250
HEATER RESISTOR POWER DISSIPATION – mW
Figure 2. PDIP Junction Temperature Rise vs. Heater
Dissipation
70
65 a. SO–8, HTR @ 5V
b. PDIP, HTR @ 5V
60 c. SO–8, HTR @ 3V
55 d. PDIP, HTR @ 3V
50
a
b
45
40
35
30
25
20 V = 5V RHEATER TO EXTERNAL
15 SUPPLY TURNED ON @ t = 5 sec
c
d
10 SO–8 SOLDERED TO .5" .3" COPPER PCB
PDIP SOLDERED TO 2" 1.31 COPPER PCB
5
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130
TIME – sec
Figure 3. Junction Temperature Rise in Still Air
140
TRANSITION FROM 100°C STIRRED
BATH TO FORCED 25°C AIR
120
V = 5V, NO LOAD, HEATER OFF
SO–8 SOLDERED TO .5" .3" Cu PCB
100
PDIP SOLDERED TO 2" 1.31" Cu PCB
80
a. PDIP PCB
b. SOIC PCB
60
a
40
b
20
0
0 100 200 300 400 500 600 700
AIR VELOCITY – FPM
Figure 4. Package Thermal Time Constant in Forced Air
120
110
TRANSITION FROM STILL 25°C
AIR TO STIRRED 100°C BATH
100
a
90
80
V = 5V, NO LOAD, HEATER OFF
70 SO–8 SOLDERED TO .5" .3" Cu PCB
60
b
PDIP SOLDERED TO 2" 1.31" Cu PCB
50
40
30 a. SO–8 PCB
20 b. PDIP PCB
10
0
0 2 4 6 8 10 12 14 16 18 20
TIME – sec
Figure 5. Thermal Response Time in Stirred Oil Bath
102
101.5
101
V+ = +5V
100.5
100
99.5
99
98.5
98
-75
-25 25 75 125
TEMPERATURE – °C
Figure 6. Heater Resistance vs. Temperature
175
REV. 0
–5–

5 Page





TMP12 arduino
TMP12
The on-board VREF output buffer is typically capable of 500 µA
output drive into as much as 50 pF load (max). Exceeding this
load will affect the accuracy of the reference voltage, could cause
thermal sensing errors due to excess heat build-up, and may induce
oscillations. External buffering of VREF with a low-drift voltage
follower will ensure optimal reference accuracy. Amplifiers which
offer low drift, low power consumption, and low cost appropriate
to this application include the OP284, and members of the OP113
and OP193 families.
With excellent drift and noise characteristics, VREF offers a good
voltage reference for data acquisition and transducer excitation ap-
plications as well. Output drift is typically better than ؊10 ppm/°C,
with 315 nV/Hz (typ) noise spectral density at 1 kHz.
Preserving Accuracy Over Wide Temperature Range Operation
The TMP12 is unique in offering both a wide-range temperature
sensor and the associated detection circuitry needed to implement
a complete thermostatic control function in one monolithic device.
The voltage reference, setpoint comparators, and output buffer
amplifiers have been carefully compensated to maintain accuracy
over the specified temperature ranges in this application. Since the
TMP12 is both sensor and control circuit, in many applications the
external components used to program and interface the device are
subjected to the same temperature extremes. Thus, it is necessary
to place components in close thermal proximity minimizing large
temperate differentials, and to account for thermal drift errors
where appropriate, such as resistor matching temperature coeffi-
cients, amplifier error drift, and the like. Circuit design with the
TMP12 requires a slightly different perspective regarding the ther-
mal behavior of electronic components.
PC Board Layout Considerations
The TMP12 also requires a different perspective on PC board lay-
out. In many applications, wide traces and generous ground planes
are used to extract heat from components. The TMP12 is slightly
different, in that ideal path for heat is via the cooling system air
flow. Thus, heat paths through the PC traces should be minimized.
This constraint implies that minimum pad sizes and trace widths
should be specified in order to reduce heat conduction. At the
same time, analog performance should not be compromised. In
particular, the bottom of the setpoint resistor ladder should be
located as close to GND as possible, as discussed in the Under-
standing Error Sources section of this data sheet.
Thermal Response Time
The time required for a temperature sensor to settle to a
specified accuracy is a function of the thermal mass of the
sensor, and the thermal conductivity between the sensor and
the object being sensed. Thermal mass is often considered
equivalent to capacitance. Thermal conductivity is commonly
specified using the symbol Q, and is the inverse of thermal
resistance. It is commonly specified in units of degrees per
watt of power transferred across the thermal joint. Figures 3
and 5 illustrate the typical RC time constant response to a
step change in ambient temperature. Thus, the time required
for the TMP12 to settle to the desired accuracy is dependent
on the package selected, the thermal contact established in
the particular application, and the equivalent thermal con-
ductivity of the heat source. For most applications, the
settling-time is probably best determined empirically.
Switching Loads with the Open-Collector Outputs
In many temperature sensing and control applications some
type of switching is required. Whether it be to turn on a
heater when the temperature goes below a minimum value
or to turn off a motor that is overheating, the open-collector
outputs can be used. For the majority of applications, the
switches used need to handle large currents on the order of
1 Amp and above. Because the TMP12 is accurately mea-
suring temperature, the open-collector outputs should
handle less than 20 mA of current to minimize self-heating.
Clearly, the trip point outputs should not drive the equip-
ment directly. Instead, an external switching device is
required to handle the large currents. Some examples of
these are relays, power MOSFETs, thyristors, IGBTs, and
Darlington transistors.
This section shows a variety of circuits where the TMP12
controls a switch. The main consideration in these circuits,
such as the relay in Figure 23, is the current required to ac-
tivate the switch.
+12V
R1
VREF
1
TEMPERATURE
SENSOR &
VOLTAGE
REFERENCE
VPTAT
8
IN4001
OR EQUIV
MOTOR
SHUTDOWN
2
R2
3
R3
4
WINDOW
COMPARATOR
HYSTERESIS
GENERATOR
TMP12
100
7
2604-12-311
COTO
6 NC
140
5 +12 V
Figure 23. Reed Relay Drive
It is important to check the particular relay you choose to
ensure that the current needed to activate the coil does not
exceed the TMP12’s recommended output current of
20 mA. This is easily determined by dividing the relay coil
voltage by the specified coil resistance. Keep in mind that
the inductance of the relay will create large voltage spikes
that can damage the TMP12 output unless protected by a
commutation diode across the coil, as shown. The relay
shown has contact rating of 10 Watts maximum. If a relay
capable of handling more power is desired, the larger con-
tacts will probably require a commensurably larger coil,
with lower coil resistance and thus higher trigger current.
As the contact power handling capability increases, so does
the current needed for the coil, In some cases an external
driving transistor should be used to remove the current load
on the TMP12 as explained in the next section.
REV. 0
–11–

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