SM72480SDX-125

SM72480 SolarMagic 1.6V, LLP-6 Factory Preset Temperature Switch and Temperature Sensor May 11, 2011 SM72480 SolarMagic 1.6V, LLP-6 Factory Preset Temperature Switch and Temperature Sensor General Description The SM72480 is a low-voltage, precision, dual-output, lowpower temperature switch and temperature sensor. The temperature trip point (TTRIP) is set at the factory to be 120°C. Built-in temperature hysteresis (THYST) keeps the output stable in an environment of temperature instability. In normal operation the SM72480 temperature switch outputs assert when the die temperature exceeds TTRIP. The temperature switch outputs will reset when the temperature falls below a temperature equal to (TTRIP − THYST). The OVERTEMP digital output, is active-high with a push-pull structure, while the OVERTEMP digital output, is active-low with an open-drain structure. The analog output, VTEMP, delivers an analog output voltage with Negative Temperature Coefficient — NTC. Driving the TRIP TEST input high: (1) causes the digital outputs to be asserted for in-situ verification and, (2) causes the threshold voltage to appear at the VTEMP output pin, which could be used to verify the temperature trip point. The SM72480's low minimum supply voltage makes it ideal for 1.8 volt system designs. Its wide operating range, low supply current , and excellent accuracy provide a temperature switch solution for a wide range of commercial and industrial applications. Features ■ Renewable Energy Grade ■ Low 1.6V operation ■ Latching function: device can latch the Over Temperature ■ ■ ■ ■ ■ condition Push-pull and open-drain temperature switch outputs Very linear analog VTEMP temperature sensor output VTEMP output short-circuit protected 2.2 mm by 2.5 mm (typ) LLP-6 package Excellent power supply noise rejection Key Specifications ■ Supply Voltage ■ Supply Current ■ Accuracy, Trip Point Temperature 1.6V to 5.5V 8 μA (typ) 0°C to 150°C 0°C to 150°C ±2.2°C ±2.3°C ±100 μA −50°C to 150°C 4.5°C to 5.5°C ■ Accuracy, VTEMP ■ VTEMP Output Drive ■ Operating Temperature ■ Hysteresis Temperature Applications ■ ■ ■ ■ ■ PV Power Optimizers Wireless Transceivers Battery Management Automotive Disk Drives Connection Diagram LLP-6 Typical Transfer Characteristic VTEMP Analog Voltage vs Die Temperature 30142001 Top View See NS Package Number SDB06A 30142024 © 2011 National Semiconductor Corporation 301420 www.national.com SM72480 Block Diagram 30142003 Pin Descriptions Pin No. Name Type Equivalent Circuit Description TRIP TEST pin. Active High input. If TRIP TEST = 0 (Default) then: VTEMP = VTS, Temperature Sensor Output Voltage If TRIP TEST = 1 then: OVERTEMP and OVERTEMP outputs are asserted and VTEMP = VTRIP, Temperature Trip Voltage. This pin may be left open if not used. Over Temperature Switch output Active High, Push-Pull Asserted when the measured temperature exceeds the Trip Point Temperature or if TRIP TEST = 1 This pin may be left open if not used. Over Temperature Switch output Active Low, Open-drain (See Section 2.1 regarding required pull-up resistor.) Asserted when the measured temperature exceeds the Trip Point Temperature or if TRIP TEST = 1 This pin may be left open if not used. 1 TRIP TEST Digital Input 5 OVERTEMP Digital Output 3 OVERTEMP Digital Output www.national.com 2 SM72480 Pin No. Name Type Equivalent Circuit Description VTEMP Analog Voltage Output If TRIP TEST = 0 then VTEMP = VTS, Temperature Sensor Output Voltage If TRIP TEST = 1 then VTEMP = VTRIP, Temperature Trip Voltage This pin may be left open if not used. Positive Supply Voltage Power Supply Ground The best thermal conductivity between the device and the PCB is achieved by soldering the DAP of the package to the thermal pad on the PCB. The thermal pad can be a floating node. However, for improved noise immunity the thermal pad should be connected to the circuit GND node, preferably directly to pin 2 (GND) of the device. 6 VTEMP Analog Output 4 2 VDD GND Power Ground DAP Die Attach Pad Typical Application 30142002 3 www.national.com SM72480 Ordering Information Order Number SM72480SD-125 SM72480SDE-125 SM72480SDX-125 SM72480SD-120 SM72480SDE-120 SM72480SDX-120 SM72480SD-105 SM72480SDE-105 SM72480SDX-105 Temperature Trip Point, °C 125°C 125°C 125°C 120°C 120°C 120°C 105°C 105°C 105°C Description 6–pin LLP 6–pin LLP 6–pin LLP 6–pin LLP 6–pin LLP 6–pin LLP 6–pin LLP 6–pin LLP 6–pin LLP NS Package Number SDB06A SDB06A SDB06A SDB06A SDB06A SDB06A SDB06A SDB06A SDB06A Package Marking 299 299 299 S80 S80 S80 701 701 701 Transport Media 1000 Units on Tape and Reel 250 Units on Tape and Reel 4500 Units on Tape and Reel 1000 Units on Tape and Reel 250 Units on Tape and Reel 4500 Units on Tape and Reel 1000 Units on Tape and Reel 250 Units on Tape and Reel 4500 Units on Tape and Reel www.national.com 4 SM72480 Absolute Maximum Ratings (Note 1) Supply Voltage −0.3V to +6.0V Voltage at OVERTEMP pin −0.3V to +6.0V Voltage at OVERTEMP and VTEMP pins −0.3V to (VDD + 0.5V) TRIP TEST Input Voltage −0.3V to (VDD + 0.5V) Output Current, any output pin ±7 mA Input Current at any pin (Note 2) 5 mA Storage Temperature −65°C to +150°C Maximum Junction Temperature TJ(MAX) +155°C ESD Susceptibility (Note 3) : Human Body Model 4500V Machine Model 300V Charged Device Model 1000V For soldering specifications: see product folder at www.national.com and www.national.com/ms/MS/MSSOLDERING.pdf Operating Ratings Specified Temperature Range: SM72480 Supply Voltage Range (VDD) (Note 1) −50°C ≤ TA ≤ +150°C  TMIN ≤ TA ≤ TMAX +1.6 V to +5.5 V 152 °C/W Thermal Resistance (θJA) (Note 4) LLP-6 (Package SDB06A) Accuracy Characteristics Trip Point Accuracy Parameter Trip Point Accuracy (Note 7) Conditions 0°C − 150°C VDD = 5.0 V Limits (Note 6) ±2.2 Units (Limit) °C (max) VTEMP Analog Temperature Sensor Output Accuracy The limits do not include DC load regulation. The stated accuracy limits are with reference to the values in the SM72480 Conversion Table. Parameter Conditions TA = 20°C to 40°C VTEMP Temperature Accuracy (Note 7) TA = 0°C to 70°C Trip Point 125°C or 120°C TA = 0°C to 90°C TA = 0°C to 120°C TA = 0°C to 150°C TA = –50°C to 0°C TA = 20°C to 40°C TA = 0°C to 70°C VTEMP Temperature Accuracy Trip Point 105°C TA = 0°C to 90°C TA = 0°C to 120°C TA = 0°C to 150°C TA = −50°C to 0°C VDD = 2.3 to 5.5 V VDD = 2.5 to 5.5 V VDD = 2.5 to 5.5 V VDD = 2.5 to 5.5 V VDD = 2.5 to 5.5 V VDD = 3.0 to 5.5 V VDD = 1.8 to 5.5 V VDD = 1.9 to 5.5 V VDD = 1.9 to 5.5 V VDD = 1.9 to 5.5 V VDD = 1.9 to 5.5 V VDD = 2.3 to 5.5 V Limits (Note 6) ±1.8 ±2.0 ±2.1 ±2.2 ±2.3 ±1.7 ±1.8 ±2.0 ±2.1 ±2.2 ±2.3 ±1.7 °C (max) °C (max) (Note 7) Units (Limit) 5 www.national.com SM72480 Electrical Characteristics Unless otherwise noted, these specifications apply for +VDD = +1.6V to +5.5V. Boldface limits apply for TA = TJ = TMIN to TMAX ; all other limits TA = TJ = 25°C. Symbol Parameter Conditions Typical (Note 5) Limits (Note 6) Units (Limit) GENERAL SPECIFICATIONS IS Quiescent Power Supply Current Hysteresis OVERTEMP DIGITAL OUTPUT ACTIVE HIGH, PUSH-PULL VDD ≥ 1.6V VDD ≥ 2.0V VOH Logic "1" Output Voltage VDD ≥ 3.3V VDD ≥ 1.6V VDD ≥ 2.0V VDD ≥ 3.3V BOTH OVERTEMP and OVERTEMP DIGITAL OUTPUTS VDD ≥ 1.6V VDD ≥ 2.0V VOL Logic "0" Output Voltage VDD ≥ 3.3V VDD ≥ 1.6V VDD ≥ 2.0V VDD ≥ 3.3V OVERTEMP DIGITAL OUTPUT IOH Logic "1" Output Leakage Current (Note 10) VTEMP Sensor Gain TA = 30 °C TA = 150 °C Trip Point = 105°C Trip Point = 125°C or 120°C Source ≤ 90 μA 1.6V ≤ VDD < 1.8V VTEMP Load Regulation (Note 9) VDD ≥ 1.8V Sink ≤ 100 μA (VDD − VTEMP) ≥ 200 mV VTEMP ≥ 260 mV Source ≤ 120 μA Sink ≤ 200 μA (VDD − VTEMP) ≥ 200 mV Sink ≤ 385 μA Sink ≤ 500 μA Sink ≤ 730 μA Sink ≤ 690 μA Sink ≤ 1.05 mA Sink ≤ 1.62 mA 0.001 0.025 -7.7 −10.3 −0.1 0.1 −0.1 0.1 1 0.29 VDD = +1.6V to +5.5V 74 −82 Without series resistor. See Section 4.2 1100 −1 1 −1 1 0.45 0.2 V (max) Source ≤ 340 μA Source ≤ 498 μA Source ≤ 780 μA Source ≤ 600 μA Source ≤ 980 μA Source ≤ 1.6 mA VDD − 0.45V V (min) VDD − 0.2V V (min) 8 5 16 5.5 4.5 μA (max) °C (max) °C (Min) ACTIVE LOW, OPEN DRAIN 1 μA (max) VTEMP ANALOG TEMPERATURE SENSOR OUTPUT mV/°C mV/°C mV (max) mV (max) mV (max) mV (max) Ohm mV μV/V dB pF (max) VTEMP ≥ 260 mV Source or Sink = 100 μA VDD Supply- to-VTEMP DC Line Regulation (Note 11) CL VTEMP Output Load Capacitance www.national.com 6 SM72480 Electrical Characteristics Unless otherwise noted, these specifications apply for +VDD = +1.6V to +5.5V. Boldface limits apply for TA = TJ = TMIN to TMAX ; all other limits TA = TJ = 25°C. Symbol Parameter Conditions Typical (Note 5) Limits (Note 6) VDD− 0.5 0.5 1.5 0.001 2.5 1 Units (Limit) V (min) V (max) μA (max) μA (max) TRIP TEST DIGITAL INPUT VIH VIL IIH IIL TIMING tEN Time from Power On to Digital Output Enabled. See definition below. Time from Power On to Analog Temperature Valid. See definition below. VTEMP CL = 0 pF to 1100 pF 1.0 2.9 ms (max) 1.1 2.3 ms (max) Logic "1" Threshold Voltage Logic "0" Threshold Voltage Logic "1" Input Current Logic "0" Input Current (Note 10) tVTEMP Definitions of tEN and tVTEMP 30142051 30142050 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: When the input voltage (VI) at any pin exceeds power supplies (VI < GND or VI > VDD), the current at that pin should be limited to 5 mA. Note 3: The Human Body Model (HBM) is a 100 pF capacitor charged to the specified voltage then discharged through a 1.5 kΩ resistor into each pin. The Machine Model (MM) is a 200 pF capacitor charged to the specified voltage then discharged directly into each pin. The Charged Device Model (CDM) is a specified circuit characterizing an ESD event that occurs when a device acquires charge through some triboelectric (frictional) or electrostatic induction processes and then abruptly touches a grounded object or surface. Note 4: The junction to ambient temperature resistance (θJA) is specified without a heat sink in still air. Note 5: Typicals are at TJ = TA = 25°C and represent most likely parametric norm. Note 6: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 7: Accuracy is defined as the error between the measured and reference output voltages, tabulated in the Conversion Table at the specified conditions of supply gain setting, voltage, and temperature (expressed in °C). Accuracy limits include line regulation within the specified conditions. Accuracy limits do not include load regulation; they assume no DC load. Note 8: Changes in output due to self heating can be computed by multiplying the internal dissipation by the temperature resistance. Note 9: Source currents are flowing out of the SM72480. Sink currents are flowing into the SM72480. Note 10: The 1 µA limit is based on a testing limitation and does not reflect the actual performance of the part. Expect to see a doubling of the current for every 15°C increase in temperature. For example, the 1 nA typical current at 25°C would increase to 16 nA at 85°C. Note 11: Line regulation (DC) is calculated by subtracting the output voltage at the highest supply voltage from the output voltage at the lowest supply voltage. The typical DC line regulation specification does not include the output voltage shift discussed in Section 4.3. Note 12: The curves shown represent typical performance under worst-case conditions. Performance improves with larger overhead (VDD − VTEMP), larger VDD, and lower temperatures. Note 13: The curves shown represent typical performance under worst-case conditions. Performance improves with larger VTEMP, larger VDD and lower temperatures. 7 www.national.com SM72480 Typical Performance Characteristics VTEMP Output Temperature Error vs. Temperature Minimum Operating Temperature vs. Supply Voltage 30142007 30142006 Supply Current vs. Temperature Supply Current vs. Supply Voltage 30142004 30142005 VTEMP Supply-Noise Rejection vs. Frequency Line Regulation VTEMP vs. Supply Voltage Trip Points 120°C 30142043 30142036 www.national.com 8 SM72480 1.0 SM72480 VTEMP vs Die Temperature Conversion Table The SM72480 has a factory-set gain, which is dependent on the Temperature Trip Point. The VTEMP temperature sensor voltage, in millivolts, at each discrete die temperature over the complete operating range is shown in the conversion table below. VTEMP Temperature Sensor Output Voltage vs Die Temperature Conversion Table The VTEMP temperature sensor output voltage, in mV, vs Die Temperature, in °C for the gain corresponding to the temperature trip point. VDD = 5.0V. VTEMP, Analog Output Voltage, mV Die Temp., TTRIP = TTRIP = 105°C °C 125 or 120°C −50 −49 −48 −47 −46 −45 −44 −43 −42 −41 −40 −39 −38 −37 −36 −35 −34 −33 −32 −31 −30 −29 −28 −27 −26 −25 −24 −23 −22 −21 −20 −19 −18 −17 −16 −15 −14 2623 2613 2603 2593 2583 2573 2563 2553 2543 2533 2523 2513 2503 2493 2483 2473 2463 2453 2443 2433 2423 2413 2403 2393 2383 2373 2363 2353 2343 2333 2323 2313 2303 2293 2283 2272 2262 1967 1960 1952 1945 1937 1930 1922 1915 1908 1900 1893 1885 1878 1870 1863 1855 1848 1840 1833 1825 1818 1810 1803 1795 1788 1780 1773 1765 1757 1750 1742 1735 1727 1720 1712 1705 1697 Die Temp., °C −13 −12 −11 −10 −9 −8 −7 −6 −5 −4 −3 −2 −1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 VTEMP, Analog Output Voltage, mV TTRIP = 125 or 120°C 2252 2242 2232 2222 2212 2202 2192 2182 2171 2161 2151 2141 2131 2121 2111 2101 2090 2080 2070 2060 2050 2040 2029 2019 2009 1999 1989 1978 1968 1958 1948 1938 1927 1917 1907 1897 1886 1876 1866 1856 1845 1835 1825 1815 1804 1794 1784 1774 TTRIP = 105°C 1690 1682 1674 1667 1659 1652 1644 1637 1629 1621 1614 1606 1599 1591 1583 1576 1568 1561 1553 1545 1538 1530 1522 1515 1507 1499 1492 1484 1477 1469 1461 1454 1446 1438 1431 1423 1415 1407 1400 1392 1384 1377 1369 1361 1354 1346 1338 1331 9 www.national.com SM72480 Die Temp., °C 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 VTEMP, Analog Output Voltage, mV TTRIP = 125 or 120°C 1763 1753 1743 1732 1722 1712 1701 1691 1681 1670 1660 1650 1639 1629 1619 1608 1598 1588 1577 1567 1557 1546 1536 1525 1515 1505 1494 1484 1473 1463 1453 1442 1432 1421 1411 1400 1390 1380 1369 1359 1348 1338 1327 1317 1306 1296 1285 1275 TTRIP = 105°C 1323 1315 1307 1300 1292 1284 1276 1269 1261 1253 1245 1238 1230 1222 1214 1207 1199 1191 1183 1176 1168 1160 1152 1144 1137 1129 1121 1113 1105 1098 1090 1082 1074 1066 1059 1051 1043 1035 1027 1019 1012 1004 996 988 980 972 964 957 Die Temp., °C 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 VTEMP, Analog Output Voltage, mV TTRIP = 125 or 120°C 1264 1254 1243 1233 1222 1212 1201 1191 1180 1170 1159 1149 1138 1128 1117 1106 1096 1085 1075 1064 1054 1043 1032 1022 1011 1001 990 979 969 958 948 937 926 916 905 894 884 873 862 852 841 831 820 809 798 788 777 766 TTRIP = 105°C 949 941 933 925 917 909 901 894 886 878 870 862 854 846 838 830 822 814 807 799 791 783 775 767 759 751 743 735 727 719 711 703 695 687 679 671 663 655 647 639 631 623 615 607 599 591 583 575 www.national.com 10 SM72480 Die Temp., °C 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 VTEMP, Analog Output Voltage, mV TTRIP = 125 or 120°C 756 745 734 724 713 702 691 681 670 659 649 638 627 616 606 595 584 573 562 552 TTRIP = 105°C 567 559 551 543 535 527 519 511 503 495 487 479 471 463 455 447 438 430 422 414 Where V is in mV, T is in °C, T1 and V1 are the coordinates of the lowest temperature, T2 and V2 are the coordinates of the highest temperature. 1.1.3 First-Order Approximation (Linear) over Small Temperature Range For a linear approximation, a line can easily be calculated over the desired temperature range from the Conversion Table using the two-point equation: 1.1.2 The First-Order Approximation (Linear) For a quicker approximation, although less accurate than the second-order, over the full operating temperature range the linear formula below can be used. Using this formula, with the constant and slope in the following set of equations, the bestfit VTEMP vs Die Temperature performance can be calculated with an approximation error less than 18 mV. VTEMP is in mV. 1.1 VTEMP vs DIE TEMPERATURE APPROXIMATIONS The SM72480's VTEMP analog temperature output is very linear. The Conversion Table above and the equation in Section 1.1.1 represent the most accurate typical performance of the VTEMP voltage output vs Temperature. 1.1.1 The Second-Order Equation (Parabolic) The data from the Conversion Table, or the equation below, when plotted, has an umbrella-shaped parabolic curve. VTEMP is in mV. Using this method of linear approximation, the transfer function can be approximated for one or more temperature ranges of interest. 11 www.national.com SM72480 2.0 OVERTEMP and OVERTEMP Digital Outputs The OVERTEMP Active High, Push-Pull Output and the OVERTEMP Active Low, Open-Drain Output both assert at the same time whenever the Die Temperature reaches the factory preset Temperature Trip Point. They also assert simultaneously whenever the TRIP TEST pin is set high. Both outputs de-assert when the die temperature goes below the Temperature Trip Point - Hysteresis. These two types of digital outputs enable the user the flexibility to choose the type of output that is most suitable for his design. Either the OVERTEMP or the OVERTEMP Digital Output pins can be left open if not used. 2.1 OVERTEMP OPEN-DRAIN DIGITAL OUTPUT The OVERTEMP Active Low, Open-Drain Digital Output, if used, requires a pull-up resistor between this pin and VDD. The following section shows how to determine the pull-up resistor value. Determining the Pull-up Resistor Value (1) We see that for VOL of 0.2 V the electrical specification for OVERTEMP shows a maximim isink of 385 µA. (2) Let iL= 1 µA, then iT is about 386 µA max. If we select 35 µA as the current limit then iT for the calculation becomes 35 µA (3) We notice that VDD(Max) is 3.3V + 0.3V = 3.6V and then calculate the pull-up resistor as RPull-up = (3.6 − 0.2)/35 µA = 97k (4) Based on this calculated value, we select the closest resistor value in the tolerance family we are using. In our example, if we are using 5% resistor values, then the next closest value is 100 kΩ. 2.2 NOISE IMMUNITY The SM72480 is virtually immune from false triggers on the OVERTEMP and OVERTEMP digital outputs due to noise on the power supply. Test have been conducted showing that, with the die temperature within 0.5°C of the temperature trip point, and the severe test of a 3 Vpp square wave "noise" signal injected on the VDD line, over the VDD range of 2V to 5V, there were no false triggers. 3.0 TRIP TEST Digital Input The TRIP TEST pin simply provides a means to test the OVERTEMP and OVERTEMP digital outputs electronically by causing them to assert, at any operating temperature, as a result of forcing the TRIP TEST pin high. When the TRIP TEST pin is pulled high the VTEMP pin will be at the VTRIP voltage. If not used, the TRIP TEST pin may either be left open or grounded. 4.0 VTEMP Analog Temperature Sensor Output 30142052 The Pull-up resistor value is calculated at the condition of maximum total current, iT, through the resistor. The total current is: The VTEMP push-pull output provides the ability to sink and source significant current. This is beneficial when, for example, driving dynamic loads like an input stage on an analogto-digital converter (ADC). In these applications the source current is required to quickly charge the input capacitor of the ADC. See the Applications Circuits section for more discussion of this topic. The SM72480 is ideal for this and other applications which require strong source or sink current. 4.1 NOISE CONSIDERATIONS The SM72480's supply-noise rejection (the ratio of the AC signal on VTEMP to the AC signal on VDD) was measured during bench tests. It's typical attenuation is shown in the Typical Performance Characteristics section. A load capacitor on the output can help to filter noise. For operation in very noisy environments, some bypass capacitance should be present on the supply within approximately 2 inches of the SM72480. 4.2 CAPACITIVE LOADS The VTEMP Output handles capacitive loading well. In an extremely noisy environment, or when driving a switched sampling input on an ADC, it may be necessary to add some filtering to minimize noise coupling. Without any precautions, the VTEMP can drive a capacitive load less than or equal to 1100 pF as shown in Figure 1. For capacitive loads greater than 1100 pF, a series resistor is required on the output, as shown in Figure 2, to maintain stable conditions. where, iT iL VOUT VDD(Max) iT is the maximum total current through the Pull-up Resistor at VOL. iL is the load current, which is very low for typical digital inputs. VOUT is the Voltage at the OVERTEMP pin. Use VOL for calculating the Pull-up resistor. VDD(Max) is the maximum power supply voltage to be used in the customer's system. The pull-up resistor maximum value can be found by using the following formula: EXAMPLE CALCULATION Suppose we have, for our example, a V DD of 3.3 V ± 0.3V, a CMOS digital input as a load, a VOL of 0.2 V. www.national.com 12 SM72480 5.0 Mounting and Temperature Conductivity The SM72480 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued or cemented to a surface. The best thermal conductivity between the device and the PCB is achieved by soldering the DAP of the package to the thermal pad on the PCB. The temperatures of the lands and traces to the other leads of the SM72480 will also affect the temperature reading. Alternatively, the SM72480 can be mounted inside a sealedend metal tube, and can then be dipped into a bath or screwed into a threaded hole in a tank. As with any IC, the SM72480 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. If moisture creates a short circuit from the VTEMP output to ground or VDD, the VTEMP output from the SM72480 will not be correct. Printed-circuit coatings are often used to ensure that moisture cannot corrode the leads or circuit traces. 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. The equation used to calculate the rise in the SM72480's die temperature is 30142015 FIGURE 1. SM72480 No Decoupling Required for Capacitive Loads Less than 1100 pF. 30142033 CLOAD 1.1 nF to 99 nF 100 nF to 999 nF 1 μF Minimum RS 3 kΩ 1.5 kΩ 800 Ω FIGURE 2. SM72480 with series resistor for capacitive loading greater than 1100 pF. 4.3 VOLTAGE SHIFT The SM72480 is very linear over temperature and supply voltage range. Due to the intrinsic behavior of an NMOS/ PMOS rail-to-rail buffer, a slight shift in the output can occur when the supply voltage is ramped over the operating range of the device. The location of the shift is determined by the relative levels of VDD and VTEMP. The shift typically occurs when VDD − VTEMP = 1.0V. This slight shift (a few millivolts) takes place over a wide change (approximately 200 mV) in VDD or VTEMP. Since the shift takes place over a wide temperature change of 5°C to 20°C, VTEMP is always monotonic. The accuracy specifications in the Electrical Characteristics table already includes this possible shift. where TA is the ambient temperature, IQ is the quiescent current, IL is the load current on the output, and VO is the output voltage. For example, in an application where TA = 30 °C, VDD = 5 V, IDD = 9 μA, Gain 4, VTEMP = 2231 mV, and IL = 2 μA, the junction temperature would be 30.021 °C, showing a self-heating error of only 0.021°C. Since the SM72480's junction temperature is the actual temperature being measured, care should be taken to minimize the load current that the VTEMP output is required to drive. If The OVERTEMP output is used with a 100 k pull-up resistor, and this output is asserted (low), then for this example the additional contribution is [(152° C/W)x(5V)2/100k] = 0.038°C for a total selfheating error of 0.059°C. Figure 3 shows the thermal resistance of the SM72480. Device Number SM72480SD NS Package Number SDB06A Thermal Resistance (θJA) 152° C/W FIGURE 3. SM72480 Thermal Resistance 13 www.national.com SM72480 6.0 Applications Circuits 30142061 FIGURE 4. Temperature Switch Using Push-Pull Output 30142062 FIGURE 5. Temperature Switch Using Open-Drain Output 30142028 Most CMOS ADCs found in microcontrollers and ASICs have a sampled data comparator input structure. When the ADC charges the sampling cap, it requires instantaneous charge from the output of the analog source such as the SM72480 temperature sensor and many op amps. This requirement is easily accommodated by the addition of a capacitor (CFILTER). The size of CFILTER depends on the size of the sampling capacitor and the sampling frequency. Since not all ADCs have identical input stages, the charge requirements will vary. This general ADC application is shown as an example only. FIGURE 6. Suggested Connection to a Sampling Analog-to-Digital Converter Input Stage www.national.com 14 SM72480 30142018 FIGURE 7. Celsius Temperature Switch 30142060 FIGURE 8. TRIP TEST Digital Output Test Circuit 30142065 The TRIP TEST pin, normally used to check the operation of the OVERTEMP and OVERTEMP pins, may be used to latch the outputs whenever the temperature exceeds the programmed limit and causes the digital outputs to assert. As shown in the figure, when OVERTEMP goes high the TRIP TEST input is also pulled high and causes OVERTEMP output to latch high and the OVERTEMP output to latch low. The latch can be released by either momentarily pulling the TRIP TEST pin low (GND), or by toggling the power supply to the device. The resistor limits the current out of the OVERTEMP output pin. FIGURE 9. Latch Circuit using OVERTEMP Output 15 www.national.com SM72480 Physical Dimensions inches (millimeters) unless otherwise noted 6-Lead LLP-6 Package NS Package Number SDB06A www.national.com 16 SM72480 Notes 17 www.national.com SM72480 SolarMagic 1.6V, LLP-6 Factory Preset Temperature Switch and Temperature Sensor Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage References PowerWise® Solutions Temperature Sensors PLL/VCO www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Quality and Reliability Feedback/Support Design Made Easy Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/training Applications & Markets Mil/Aero PowerWise® Design University Serial Digital Interface (SDI) www.national.com/sdi www.national.com/wireless www.national.com/tempsensors SolarMagic™ THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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