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LM20SITL Datasheet(PDF) 7 Page - Texas Instruments |
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LM20SITL Datasheet(HTML) 7 Page - Texas Instruments |
7 / 18 page LM20 www.ti.com SNIS106P – DECEMBER 1999 – REVISED FEBRUARY 2013 where T is the middle of the temperature range of interest and m is in V/°C. For example for the temperature range of TMIN = −30 to TMAX = +100°C: T = 35°C (5) and m = −11.77 mV/°C (6) The offset of the linear transfer function can be calculated using the following equation: b = (VOP(TMAX) + VOP(T) − m × (TMAX+T))/2 (7) where: • VOP(TMAX) is the calculated output voltage at TMAX using the parabolic transfer function for VO • VOP(T) is the calculated output voltage at T using the parabolic transfer function for VO. Using this procedure the best fit linear transfer function for many popular temperature ranges was calculated in Table 2. As shown in Table 2 the error that is introduced by the linear transfer function increases with wider temperature ranges. Table 2. First Order Equations Optimized for Different Temperature Ranges Temperature Range Linear Equation Maximum Deviation of Linear Equation from VO = Parabolic Equation (°C) Tmin (°C) Tmax (°C) −55 130 −11.79 mV/°C × T + 1.8528 V ±1.41 −40 110 −11.77 mV/°C × T + 1.8577 V ±0.93 −30 100 −11.77 mV/°C × T + 1.8605 V ±0.70 -40 85 −11.67 mV/°C × T + 1.8583 V ±0.65 −10 65 −11.71 mV/°C × T + 1.8641 V ±0.23 35 45 −11.81 mV/°C × T + 1.8701 V ±0.004 20 30 –11.69 mV/°C × T + 1.8663 V ±0.004 Mounting The LM20 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 LM20 is sensing will be within about +0.02°C of the surface temperature to which the LM20'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 measured would be at an intermediate temperature between the surface temperature and the air temperature. To ensure good thermal conductivity the backside of the LM20 die is directly attached to the pin 2 GND pin. The tempertures of the lands and traces to the other leads of the LM20 will also affect the temperature that is being sensed. Alternatively, the LM20 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 LM20 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 LM20 or its connections. The thermal resistance junction to ambient ( θJA) is the parameter used to calculate the rise of a device junction temperature due to its power dissipation. For the LM20 the equation used to calculate the rise in the die temperature is as follows: TJ = TA + θJA [(V + I Q) + (V + − V O) IL] where IQ is the quiescent current and ILis the load current on the output. Since the LM20's junction temperature is the actual temperature being measured care should be taken to minimize the load current that the LM20 is required to drive. The tables shown in Table 3 summarize the rise in die temperature of the LM20 without any loading, and the thermal resistance for different conditions. Copyright © 1999–2013, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: LM20 |
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