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ADW75001Z-0REEL7 Datasheet(Arkusz danych) 9 Page - Analog Devices

Numer części ADW75001Z-0REEL7
Szczegółowy opis  Low Voltage Temperature Sensors
Pobierz  20 Pages
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Producent  AD [Analog Devices]
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 9 page
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Rev. F | Page 9 of 20
All TMP3x devices include a shutdown capability, which
reduces the power supply drain to less than 0.5 μA maximum.
This feature, available only in the SOIC_N and the SOT-23
packages, is TTL/CMOS level-compatible, provided that the
temperature sensor supply voltage is equal in magnitude to the
logic supply voltage. Internal to the TMP3x at the SHUTDOWN
pin, a pull-up current source to +VS is connected. This allows
the SHUTDOWN pin to be driven from an open-collector/drain
driver. A logic low, or zero-volt condition, on the SHUTDOWN
pin is required to turn off the output stage. During shutdown,
the output of the temperature sensors becomes high impedance
where the potential of the output pin is then determined by
external circuitry. If the shutdown feature is not used, it is
recommended that the SHUTDOWN pin be connected to +VS
(Pin 8 on the SOIC_N; Pin 2 on the SOT-23).
The shutdown response time of these temperature sensors is
shown in Figure 14, Figure 15, and Figure 16.
If the TMP3x temperature sensors are thermally attached and
protected, they can be used in any temperature measurement
application where the maximum temperature range of the
medium is between −40°C and +125°C. Properly cemented or
glued to the surface of the medium, these sensors are within
0.01°C of the surface temperature. Caution should be exercised,
especially with T-3 packages, because the leads and any wiring
to the device can act as heat pipes, introducing errors if the
surrounding air-surface interface is not isothermal. Avoiding this
condition is easily achieved by dabbing the leads of the temper-
ature sensor and the hookup wires with a bead of thermally
conductive epoxy. This ensures that the TMP3x die temperature
is not affected by the surrounding air temperature. Because
plastic IC packaging technology is used, excessive mechanical
stress should be avoided when fastening the device with a clamp
or a screw-on heat tab. Thermally conductive epoxy or glue,
which must be electrically nonconductive, is recommended
under typical mounting conditions.
These temperature sensors, as well as any associated circuitry,
should be kept insulated and dry to avoid leakage and corrosion.
In wet or corrosive environments, any electrically isolated metal
or ceramic well can be used to shield the temperature sensors.
Condensation at very cold temperatures can cause errors and
should be avoided by sealing the device, using electrically non-
conductive epoxy paints or dip or any one of the many printed
circuit board coatings and varnishes.
The thermal environment in which the TMP3x sensors are used
determines two important characteristics: self-heating effects
and thermal response time. Figure 23 illustrates a thermal model
of the TMP3x temperature sensors, which is useful in under-
standing these characteristics.
Figure 23. Thermal Circuit Model
In the T-3 package, the thermal resistance junction-to-case, θJC,
is 120°C/W. The thermal resistance case-to-ambient, CA, is the
difference between θJA and θJC, and is determined by the char-
acteristics of the thermal connection. The power dissipation of
the temperature sensor, PD, is the product of the total voltage
across the device and its total supply current, including any
current delivered to the load. The rise in die temperature above
the ambient temperature of the medium is given by
TJ = PD × (θJC + θCA) + TA
Thus, the die temperature rise of a TMP35 SOT-23 package
mounted into a socket in still air at 25°C and driven from a 5 V
supply is less than 0.04°C.
The transient response of the TMP3x sensors to a step change
in the temperature is determined by the thermal resistances and
the thermal capacities of the die, CCH, and the case, CC. The
thermal capacity of CC varies with the measurement medium
because it includes anything in direct contact with the package.
In all practical cases, the thermal capacity of CC is the limiting
factor in the thermal response time of the sensor and can be
represented by a single-pole RC time constant response. Figure
17 and Figure 19 show the thermal response time of the TMP3x
sensors under various conditions. The thermal time constant
of a temperature sensor is defined as the time required for the
sensor to reach 63.2% of the final value for a step change in the
temperature. For example, the thermal time constant of a
TMP35 SOIC package sensor mounted onto a 0.5" × 0.3" PCB is
less than 50 sec in air, whereas in a stirred oil bath, the time
constant is less than 3 sec.

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