SNIS175A March   2013  – January 2015 LMT88

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 LMT88 Transfer Function
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Capacitive Loads
    2. 8.2 Typical Applications
      1. 8.2.1 Full-Range Centigrade Temperature Sensor
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Centigrade Thermostat
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curve
    3. 8.3 System Examples
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7 Detailed Description

7.1 Overview

The LMT88 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 LMT88 is predominately linear, yet has a slight predictable parabolic curvature. The accuracy of the LMT88 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 LMT88 quiescent current is less than 10 μA. Therefore, self-heating is less than 0.02°C in still air. Shutdown capability for the LMT88 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.

7.2 Functional Block Diagram

FBD_01_SNIS175.gif

7.3 Feature Description

7.3.1 LMT88 Transfer Function

The LMT88 transfer function can be described in different ways with varying levels of precision. A simple linear transfer function, with good accuracy near 25°C, is:

Equation 1. VO = −11.69 mV/°C × T + 1.8663 V

Over the full operating temperature range of −55°C to 130°C, best accuracy can be obtained by using the parabolic transfer function.

Equation 2. VO = (−3.88×10−6×T2) + (−1.15×10−2×T) + 1.8639

solving for T:

Equation 3. equation_3_nis176.gif

Using Equation 2 the following temperature to voltage output characteristic table can be generated.

Table 1. Temperature to Voltage Output Characteristic Table

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:

Equation 4. equation_3_nis175.gif

For other methods of calculating T see Detailed Design Procedure.

7.4 Device Functional Modes

The LMT88's only functional mode is that it has an analog output inversely proportional to temperature.