LM50

LM50 SOT-23 Single-Supply Centigrade Temperature Sensor February 2006 LM50 SOT-23 Single-Supply Centigrade Temperature Sensor General Description The LM50 is a precision integrated-circuit temperature sensor that can sense a −40˚C to +125˚C temperature range using a single positive supply. The LM50’s output voltage is linearly proportional to Celsius (Centigrade) temperature (+10 mV/˚C) and has a DC offset of +500 mV. The offset allows reading negative temperatures without the need for a negative supply. The ideal output voltage of the LM50 ranges from +100 mV to +1.75V for a −40˚C to +125˚C temperature range. The LM50 does not require any external calibration or trimming to provide accuracies of ± 3˚C at room temperature and ± 4˚C over the full −40˚C to +125˚C temperature range. Trimming and calibration of the LM50 at the wafer level assure low cost and high accuracy. The LM50’s linear output, +500 mV offset, and factory calibration simplify circuitry required in a single supply environment where reading negative temperatures is required. Because the LM50’s quiescent current is less than 130 µA, self-heating is limited to a very low 0.2˚C in still air. Applications n n n n n n n n n Computers Disk Drives Battery Management Automotive FAX Machines Printers Portable Medical Instruments HVAC Power Supply Modules Features n n n n n n n n n n n Calibrated directly in degree Celsius (Centigrade) Linear + 10.0 mV/˚C scale factor ± 2˚C accuracy guaranteed at +25˚C Specified for full −40˚ to +125˚C range Suitable for remote applications Low cost due to wafer-level trimming Operates from 4.5V to 10V Less than 130 µA current drain Low self-heating, less than 0.2˚C in still air Nonlinearity less than 0.8˚C over temp UL Recognized Component Connection Diagram SOT-23 Order Number LM50BIM3 LM50CIM3 01203001 Device Top Mark T5B T5C T5B T5C Supplied As 1000 Units on Tape and Reel 1000 Units on Tape and Reel 3000 Units on Tape and Reel 3000 Units on Tape and Reel Top View See NS Package Number mf03A LM50BIM3X LM50CIM3X © 2006 National Semiconductor Corporation DS012030 www.national.com LM50 Typical Application 01203003 FIGURE 1. Full-Range Centigrade Temperature Sensor (−40˚C to +125˚C) www.national.com 2 LM50 Absolute Maximum Ratings (Note 1) Supply Voltage Output Voltage Output Current Storage Temperature TJMAX, Maximum Junction Temperature ESD Susceptibility (Note 3): Human Body Model Machine Model 150˚C 2000V 250V +12V to −0.2V (+VS + 0.6V) to −1.0V 10 mA −65˚C to +150˚C Operating Ratings (Note 1) Specified Temperature Range: LM50C LM50B Operating Temperature Range θJA (Note 4) Supply Voltage Range (+VS) TMIN to TMAX −40˚C to +125˚C −25˚C to +100˚C −40˚C to +150˚C 450˚C/W +4.5V to +10V Soldering process must comply with National Semiconductor’s Reflow Temperature Profile specifications. Refer to www.national.com/packaging. (Note 2) Electrical Characteristics Unless otherwise noted, these specifications apply for VS = +5 VDC and ILOAD = +0.5 µA, in the circuit of Figure 1. Boldface limits apply for the specified TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25˚C, unless otherwise noted. Parameter Conditions Typical Accuracy (Note 6) Nonlinearity (Note 7) Sensor Gain (Average Slope) Output Resistance Line Regulation (Note 8) Quiescent Current (Note 9) Change of Quiescent Current (Note 9) Temperature Coefficient of Quiescent Current Long Term Stability (Note 10) TJ = 125˚C, for 1000 hours Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating the device beyond its rated operating conditions. Note 2: Reflow temperature profiles are different for lead-free and non-lead-free packages. Note 3: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine model, 200 pF discharged directly into each pin. Note 4: Thermal resistance of the SOT-23 package is specified without a heat sink, junction to ambient. Note 5: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 6: Accuracy is defined as the error between the output voltage and 10mv/˚C times the device’s case temperature plus 500 mV, at specified conditions of voltage, current, and temperature (expressed in ˚C). Note 7: Nonlinearity is defined as the deviation of the output-voltage-versus-temperature curve from the best-fit straight line, over the device’s rated temperature range. Note 8: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output due to heating effects can be computed by multiplying the internal dissipation by the thermal resistance. Note 9: Quiescent current is defined in the circuit of Figure 1 . Note 10: For best long-term stability, any precision circuit will give best results if the unit is aged at a warm temperature, and/or temperature cycled for at least 46 hours before long-term life test begins. This is especially true when a small (Surface-Mount) part is wave-soldered; allow time for stress relaxation to occur. The majority of the drift will occur in the first 1000 hours at elevated temperatures. The drift after 1000 hours will not continue at the first 1000 hour rate. LM50B Limit (Note 5) LM50C Typical Limit (Note 5) Units (Limit) ˚C (max) ˚C (max) ˚C (max) ˚C (max) mV/˚C (min) mV/˚C (max) Ω (max) mV/V (max) mV/V (max) µA (max) µA (max) µA (max) µA/˚C ˚C TA = +25˚C TA = TMAX TA = TMIN ± 2.0 ± 3.0 +3.0, −3.5 ± 0.8 +9.7 +10.3 2000 +4.5V ≤ VS ≤ +10V +4.5V ≤ VS ≤ +10V +4.5V ≤ VS ≤ +10V +1.0 4000 2000 ± 3.0 ± 4.0 ± 4.0 ± 0.8 +9.7 +10.3 4000 ± 0.8 ± 1.2 130 180 2.0 +2.0 ± 0.8 ± 1.2 130 180 2.0 ± 0.08 ± 0.08 3 www.national.com LM50 Typical Performance Characteristics circuit board as shown in Figure 2. Thermal Resistance Junction to Air To generate these curves the LM50 was mounted to a printed Thermal Time Constant 01203021 01203022 Thermal Response in Still Air with Heat Sink (Figure 2) Thermal Response in Stirred Oil Bath with Heat Sink 01203023 01203024 Start-Up Voltage vs Temperature Thermal Response in Still Air without a Heat Sink 01203025 01203026 www.national.com 4 LM50 Typical Performance Characteristics To generate these curves the LM50 was mounted to a printed circuit board as shown in Figure 2. (Continued) Quiescent Current vs Temperature (Figure 1) Accuracy vs Temperature 01203027 01203028 Noise Voltage Supply Voltage vs Supply Current 01203029 01203030 Start-Up Response 01203031 5 www.national.com LM50 Printed Circuit Board Temperature Rise of LM50 Due to Self-Heating (Thermal Resistance, θJA) SOT-23 no heat sink* Still air Moving air 450˚C/W SOT-23 small heat fin** 260˚C/W 180˚C/W * Part soldered to 30 gauge wire. ** Heat sink used is 1⁄2" square printed circuit board with 2 oz. foil with part attached as shown in Figure 2. 2.0 Capacitive Loads 01203019 FIGURE 2. Printed Circuit Board Used for Heat Sink to Generate All Curves. 1⁄2" Square Printed Circuit Board with 2 oz. Foil or Similar 01203007 FIGURE 3. LM50 No Decoupling Required for Capacitive Load 1.0 Mounting The LM50 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued or cemented to a surface and its temperature will be within about 0.2˚C of the surface temperature. 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 LM50 die would be at an intermediate temperature between the surface temperature and the air temperature. To ensure good thermal conductivity the backside of the LM50 die is directly attached to the GND pin. The lands and traces to the LM50 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 LM50s temperature to deviate from the desired temperature. Alternatively, the LM50 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 LM50 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 LM50 or its connections. 01203008 FIGURE 4. LM50C with Filter for Noisy Environment The LM50 handles capacitive loading very well. Without any special precautions, the LM50 can drive any capacitive load. The LM50 has a nominal 2 kΩ output impedance (as can be seen in the block diagram). The temperature coefficient of the output resistors is around 1300 ppm/˚C. Taking into account this temperature coefficient and the initial tolerance of the resistors the output impedance of the LM50 will not exceed 4 kΩ. 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 VIN to GND to bypass the power supply voltage, as shown in Figure 4. In a noisy environment it may be necessary to add a capacitor from the output to ground. A 1 µF output capacitor with the 4 kΩ output impedance will form a 40 Hz lowpass filter. Since the thermal time constant of the LM50 is much slower than the 25 ms time constant formed by the RC, the overall response time of the LM50 will not be significantly affected. For much larger capacitors this additional time lag will increase the overall response time of the LM50. www.national.com 6 LM50 2.0 Capacitive Loads (Continued) 01203017 *R2 ≈ 2k with a typical 1300 ppm/˚C drift. FIGURE 5. Block Diagram 3.0 Typical Applications 01203011 FIGURE 6. Centigrade Thermostat/Fan Controller 01203013 FIGURE 7. Temperature To Digital Converter (Serial Output) (+125˚C Full Scale) 7 www.national.com LM50 3.0 Typical Applications (Continued) 01203014 FIGURE 8. Temperature To Digital Converter (Parallel TRI-STATE ® Outputs for Standard Data Bus to µP Interface) (125˚C Full Scale) 01203016 FIGURE 9. LM50 With Voltage-To-Frequency Converter And Isolated Output (−40˚C to +125˚C; 100 Hz to 1750 Hz) www.national.com 8 LM50 SOT-23 Single-Supply Centigrade Temperature Sensor Physical Dimensions inches (millimeters) unless otherwise noted SOT-23 Molded Small Outline Transistor Package (M3) Order Number LM50BIM3, or LM50CIM3 NS Package Number mf03a National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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