SM73710 Datasheet, PDF (8/12 Pages) Texas Instruments – SM73710 2.7V, SOT-23 Temperature Sensor

SM73710
SNOSBA1A – OCTOBER 2011 – REVISED APRIL 2013
MOUNTING
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The SM73710 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be
glued or cemented to a surface. The temperature that the SM73710 is sensing will be within about +0.1°C of the
surface temperature that SM73710's leads are attached to.
This presumes that the ambient air temperature is almost the same as the surface temperature; if the air
temperature were much higher or lower than the surface temperature, the actual temperature of the SM73710
die would be at an intermediate temperature between the surface temperature and the air temperature.
To ensure good thermal conductivity the backside of the SM73710 die is directly attached to the GND pin. The
lands and traces to the SM73710 will, of course, be part of the printed circuit board, which is the object whose
temperature is being measured. These printed circuit board lands and traces will not cause the SM73710's
temperature to deviate from the desired temperature.
Alternatively, the SM73710 can be mounted inside a sealed-end metal tube, and can then be dipped into a bath
or screwed into a threaded hole in a tank. As with any IC, the SM73710 and accompanying wiring and circuits
must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate
at cold temperatures where condensation can occur. Printed-circuit coatings and varnishes such as Humiseal
and epoxy paints or dips are often used to ensure that moisture cannot corrode the SM73710 or its connections.
The thermal resistance junction to ambient (θ_JA ) is the parameter used to calculate the rise of a device junction
temperature due to the device power dissipation. For the SM73710 the equation used to calculate the rise in the
die temperature is as follows:
T_J = T_A + θ _JA [(+V_S I_Q) + (+V_S − V_O) I_L]
where I_Q is the quiescent current and I_Lis the load current on the output.
The table shown in Table 2 summarizes the rise in die temperature of the SM73710 without any loading, and the
thermal resistance for different conditions.
Table 2. Temperature Rise of SM73710 Due to Self-Heating and Thermal Resistance (θ_JA)
SOT-23 ⁽¹⁾
SOT-23 ⁽²⁾
no heat sink
small heat fin
θ _JA
(°C/W)
T _J − T_A
(°C)
θ _JA
(°C/W)
T _J − T_A
(°C)
Still air
450
0.17
260
0.1
Moving air
180
0.07
(1) Part soldered to 30 gauge wire.
(2) Heat sink used is ½″ square printed circuit board with 2 oz. foil with part attached as shown in Figure 14 .
Capacitive Loads
The SM73710 handles capacitive loading well. Without any special precautions, the SM73710 can drive any
capacitive load as shown in Figure 15. Over the specified temperature range the SM73710 has a maximum
output impedance of 800Ω. In an extremely noisy environment it may be necessary to add some filtering to
minimize noise pickup. It is recommended that 0.1 μF be added from +V _S to GND to bypass the power supply
voltage, as shown in Figure 16. In a noisy environment it may be necessary to add a capacitor from the output to
ground. A 1 μF output capacitor with the 800Ω output impedance will form a 199 Hz lowpass filter. Since the
thermal time constant of the SM73710 is much slower than the 6.3 ms time constant formed by the RC, the
overall response time of the SM73710 will not be significantly affected. For much larger capacitors this additional
time lag will increase the overall response time of the SM73710.
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