SNIS176A March 2013 – January 2015 LMT89
PRODUCTION DATA.
The LMT89 device is a precision analog output CMOS integrated-circuit temperature sensor that operates over a temperature range of −55°C to 130°C . The power supply operating range is 2.4 V to 5.5 V. The transfer function of LMT89 is predominately linear, yet has a slight predictable parabolic curvature. The accuracy of the LMT89 device, when specified to a parabolic transfer function, is typically ±1.5°C at an ambient temperature of 30°C. The temperature error increases linearly and reaches a maximum of ±5°C at the temperature range extremes. The temperature range is affected by the power supply voltage. At a power supply voltage of 2.7 V to 5.5 V, the temperature range extremes are 130°C and −55°C. Decreasing the power supply voltage to 2.4 V changes the negative extreme to −30°C, while the positive remains at 130°C.
The LMT89 quiescent current is less than 10 μA. Therefore, self-heating is less than 0.02°C in still air. Shutdown capability for the LMT89 is intrinsic because its inherent low power consumption allows it to be powered directly from the output of many logic gates or does not necessitate shutdown at all.
The temperature sensing element is comprised of a simple base emitter junction that is forward biased by a current source. The temperature sensing element is then buffered by an amplifier and provided to the OUT pin. The amplifier has a simple class A output stage thus providing a low impedance output that can source 16 µA and sink 1 µA.
The transfer function of the LMT89 device can be described in different ways with varying levels of precision. A simple linear transfer function with good accuracy near 25°C is shown in Equation 1.
Over the full operating temperature range of −55°C to 130°C, best accuracy can be obtained by using the parabolic transfer function.
Using Equation 2 the following temperature to voltage output characteristic table can be generated.
TEMP (°C) |
VOUT (V) |
TEMP (°C) |
VOUT (V) |
TEMP (°C) |
VOUT (V) |
TEMP (°C) |
VOUT (V) |
TEMP (°C) |
VOUT (V) |
TEMP (°C) |
VOUT (V) |
TEMP (°C) |
VOUT (V) |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
–55 | 2.4847 | –28 | 2.1829 | –1 | 1.8754 | 26 | 1.5623 | 53 | 1.2435 | 80 | 0.9191 | 107 | 0.5890 |
–54 | 2.4736 | –27 | 2.1716 | 0 | 1.8639 | 27 | 1.5506 | 54 | 1.2316 | 81 | 0.9069 | 108 | 0.5766 |
–53 | 2.4625 | –26 | 2.1603 | 1 | 1.8524 | 28 | 1.5389 | 55 | 1.2197 | 82 | 0.8948 | 109 | 0.5643 |
–52 | 2.4514 | –25 | 2.1490 | 2 | 1.8409 | 29 | 1.5271 | 56 | 1.2077 | 83 | 0.8827 | 110 | 0.5520 |
–51 | 2.4403 | –24 | 2.1377 | 3 | 1.8294 | 30 | 1.5154 | 57 | 1.1958 | 84 | 0.8705 | 111 | 0.5396 |
–50 | 2.4292 | –23 | 2.1263 | 4 | 1.8178 | 31 | 1.5037 | 58 | 1.1838 | 85 | 0.8584 | 112 | 0.5272 |
–49 | 2.4181 | –22 | 2.1150 | 5 | 1.8063 | 32 | 1.4919 | 59 | 1.1719 | 86 | 0.8462 | 113 | 0.5149 |
–48 | 2.4070 | –21 | 2.1037 | 6 | 1.7948 | 33 | 1.4802 | 60 | 1.1599 | 87 | 0.8340 | 114 | 0.5025 |
–47 | 2.3958 | –20 | 2.0923 | 7 | 1.7832 | 34 | 1.4684 | 61 | 1.1480 | 88 | 0.8219 | 115 | 0.4901 |
–46 | 2.3847 | –19 | 2.0810 | 8 | 1.7717 | 35 | 1.4566 | 62 | 1.1360 | 89 | 0.8097 | 116 | 0.4777 |
–45 | 2.3735 | –18 | 2.0696 | 9 | 1.7601 | 36 | 1.4449 | 63 | 1.1240 | 90 | 0.7975 | 117 | 0.4653 |
–44 | 2.3624 | –17 | 2.0583 | 10 | 1.7485 | 37 | 1.4331 | 64 | 1.1120 | 91 | 0.7853 | 118 | 0.4529 |
–43 | 2.3512 | –16 | 2.0469 | 11 | 1.7369 | 38 | 1.4213 | 65 | 1.1000 | 92 | 0.7731 | 119 | 0.4405 |
–42 | 2.3401 | –15 | 2.0355 | 12 | 1.7253 | 39 | 1.4095 | 66 | 1.0880 | 93 | 0.7608 | 120 | 0.4280 |
–41 | 2.3289 | –14 | 2.0241 | 13 | 1.7137 | 40 | 1.3977 | 67 | 1.0760 | 94 | 0.7486 | 121 | 0.4156 |
–40 | 2.3177 | –13 | 2.0127 | 14 | 1.7021 | 41 | 1.3859 | 68 | 1.0640 | 95 | 0.7364 | 122 | 0.4032 |
–39 | 2.3065 | –12 | 2.0013 | 15 | 1.6905 | 42 | 1.3741 | 69 | 1.0519 | 96 | 0.7241 | 123 | 0.3907 |
–38 | 2.2953 | –11 | 1.9899 | 16 | 1.6789 | 43 | 1.3622 | 70 | 1.0399 | 97 | 0.7119 | 124 | 0.3782 |
–37 | 2.2841 | –10 | 1.9785 | 17 | 1.6673 | 44 | 1.3504 | 71 | 1.0278 | 98 | 0.6996 | 125 | 0.3658 |
–36 | 2.2729 | –9 | 1.9671 | 18 | 1.6556 | 45 | 1.3385 | 72 | 1.0158 | 99 | 0.6874 | 126 | 0.3533 |
–35 | 2.2616 | –8 | 1.9557 | 19 | 1.6440 | 46 | 1.3267 | 73 | 1.0037 | 100 | 0.6751 | 127 | 0.3408 |
–34 | 2.2504 | –7 | 1.9442 | 20 | 1.6323 | 47 | 1.3148 | 74 | 0.9917 | 101 | 0.6628 | 128 | 0.3283 |
–33 | 2.2392 | –6 | 1.9328 | 21 | 1.6207 | 48 | 1.3030 | 75 | 0.9796 | 102 | 0.6505 | 129 | 0.3158 |
–32 | 2.2279 | –5 | 1.9213 | 22 | 1.6090 | 49 | 1.2911 | 76 | 0.9675 | 103 | 0.6382 | 130 | 0.3033 |
–31 | 2.2167 | –4 | 1.9098 | 23 | 1.5973 | 50 | 1.2792 | 77 | 0.9554 | 104 | 0.6259 | — | — |
–30 | 2.2054 | –3 | 1.8984 | 24 | 1.5857 | 51 | 1.2673 | 78 | 0.9433 | 105 | 0.6136 | — | — |
–29 | 2.1941 | –2 | 1.8869 | 25 | 1.5740 | 52 | 1.2554 | 79 | 0.9312 | 106 | 0.6013 | — | — |
Solving Equation 2 for T:
For other methods of calculating T, see Detailed Design Procedure.
The only functional mode of the LMT89 device is that it has an analog output inversely proportional to temperature.