SNIS144G July   2007  – September 2016 LM26LV , LM26LV-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings: LM26LV
    3. 6.3 ESD Ratings: LM26LV-Q1
    4. 6.4 Recommended Operating Conditions
    5. 6.5 Thermal Information
    6. 6.6 Electrical Characteristics
    7. 6.7 Switching Characteristics
    8. 6.8 Accuracy Characteristics
    9. 6.9 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 LM26LV and LM26LV-Q1 VTEMP vs Die Temperature Conversion Table
      2. 7.3.2 VTEMP vs Die Temperature Approximations
        1. 7.3.2.1 The Second-Order Equation (Parabolic)
        2. 7.3.2.2 The First-Order Approximation (Linear)
        3. 7.3.2.3 First-Order Approximation (Linear) Over Small Temperature Range
      3. 7.3.3 OVERTEMP and OVERTEMP Digital Outputs
        1. 7.3.3.1 OVERTEMP Open-Drain Digital Output
          1. 7.3.3.1.1 Determining the Pullup Resistor Value
            1. 7.3.3.1.1.1 Example Calculation
      4. 7.3.4 TRIP_TEST Digital Input
      5. 7.3.5 VTEMP Analog Temperature Sensor Output
        1. 7.3.5.1 Noise Considerations
        2. 7.3.5.2 Capacitive Loads
        3. 7.3.5.3 Voltage Shift
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 ADC Input Considerations
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
    1. 9.1 Power Supply Noise Immunity
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Mounting and Temperature Conductivity
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Related Links
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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7 Detailed Description

7.1 Overview

The LM26LV and LM26LV-Q1 are precision, dual-output, temperature switches with analog temperature sensor output. The trip temperature (TTRIP) is factory selected by the order number. The VTEMP class AB analog output provides a voltage that is proportional to temperature. The LM26LV and LM26LV-Q1 include an internal reference DAC (TEMP THRESHOLD), analog temperature sensor and analog comparator. The reference DAC is connected to one of the comparator inputs. The reference DAC output voltage (VTRIP) is preprogrammed by TI. The result of the reference DAC voltage and the temperature sensor output comparison is provided on two output pins OVERTEMP and OVERTEMP.

The VTEMP output has a programmable gain. The output gain has 4 possible settings as described in Table 1. The gain setting is dependent on the temperature trip point selected.

Built-in temperature hysteresis (THYST) prevents the digital outputs from oscillating. The OVERTEMP and OVERTEMP activates when the die temperature exceeds TTRIP and releases when the temperature falls below a temperature equal to TTRIP minus THYST. OVERTEMP is active-high with a push-pull structure. OVERTEMP, is active-low with an open-drain structure. The comparator hysteresis is fixed at 5°C.

Driving the TRIP-TEST high activates the digital outputs. A processor can check the logic level of the OVERTEMP or OVERTEMP, confirming that they changed to their active state. This allows for system production testing verification that the comparator and output circuitry are functional after system assembly. When the TRIP-TEST pin is high, the trip-level reference voltage appears at the VTEMP pin. Tying OVERTEMP to TRIP-TEST latches the output after it trips. It can be cleared by forcing TRIP-TEST low or powering off the LM26LV or LM26LV-Q1.

7.2 Functional Block Diagram

LM26LV LM26LV-Q1 20204703.gif

7.3 Feature Description

7.3.1 LM26LV and LM26LV-Q1 VTEMP vs Die Temperature Conversion Table

The LM26LV and LM26LV-Q1 have one out of four possible factory-set gains, Gain 1 through Gain 4, depending on the range of the Temperature Trip Point. The VTEMP temperature sensor voltage, in millivolts, at each discrete die temperature over the complete operating temperature range, and for each of the four Temperature Trip Point ranges, is shown in Table 1. This table is the reference from which the LM26LV and LM26LV-Q1 accuracy specifications (listed in Accuracy Characteristics) are determined. This table can be used, for example, in a host processor look-up table. See The Second-Order Equation (Parabolic) for the parabolic equation used in the Conversion Table.

Table 1. VTEMP Temperature Sensor Output Voltage vs Die Temperature Conversion Table

DIE TEMPERATURE (°C) ANALOG OUTPUT VOLTAGE, VTEMP (mV)(1)
GAIN 1 GAIN 2 GAIN 3 GAIN 4
–50 1312 1967 2623 3278
–49 1307 1960 2613 3266
–48 1302 1952 2603 3253
–47 1297 1945 2593 3241
–46 1292 1937 2583 3229
–45 1287 1930 2573 3216
–44 1282 1922 2563 3204
–43 1277 1915 2553 3191
–42 1272 1908 2543 3179
–41 1267 1900 2533 3166
–40 1262 1893 2523 3154
–39 1257 1885 2513 3141
–38 1252 1878 2503 3129
–37 1247 1870 2493 3116
–36 1242 1863 2483 3104
–35 1237 1855 2473 3091
–34 1232 1848 2463 3079
–33 1227 1840 2453 3066
–32 1222 1833 2443 3054
–31 1217 1825 2433 3041
–30 1212 1818 2423 3029
–29 1207 1810 2413 3016
–28 1202 1803 2403 3004
–27 1197 1795 2393 2991
–26 1192 1788 2383 2979
–25 1187 1780 2373 2966
–24 1182 1773 2363 2954
–23 1177 1765 2353 2941
–22 1172 1757 2343 2929
–21 1167 1750 2333 2916
–20 1162 1742 2323 2903
–19 1157 1735 2313 2891
–18 1152 1727 2303 2878
–17 1147 1720 2293 2866
–16 1142 1712 2283 2853
–15 1137 1705 2272 2841
–14 1132 1697 2262 2828
–13 1127 1690 2252 2815
–12 1122 1682 2242 2803
–11 1116 1674 2232 2790
–10 1111 1667 2222 2777
–9 1106 1659 2212 2765
–8 1101 1652 2202 2752
–7 1096 1644 2192 2740
–6 1091 1637 2182 2727
–5 1086 1629 2171 2714
–4 1081 1621 2161 2702
–3 1076 1614 2151 2689
–2 1071 1606 2141 2676
–1 1066 1599 2131 2664
0 1061 1591 2121 2651
1 1056 1583 2111 2638
2 1051 1576 2101 2626
3 1046 1568 2090 2613
4 1041 1561 2080 2600
5 1035 1553 2070 2587
6 1030 1545 2060 2575
7 1025 1538 2050 2562
8 1020 1530 2040 2549
9 1015 1522 2029 2537
10 1010 1515 2019 2524
11 1005 1507 2009 2511
12 1000 1499 1999 2498
13 995 1492 1989 2486
14 990 1484 1978 2473
15 985 1477 1968 2460
16 980 1469 1958 2447
17 974 1461 1948 2435
18 969 1454 1938 2422
19 964 1446 1927 2409
20 959 1438 1917 2396
21 954 1431 1907 2383
22 949 1423 1897 2371
23 944 1415 1886 2358
24 939 1407 1876 2345
25 934 1400 1866 2332
26 928 1392 1856 2319
27 923 1384 1845 2307
28 918 1377 1835 2294
29 913 1369 1825 2281
30 908 1361 1815 2268
31 903 1354 1804 2255
32 898 1346 1794 2242
33 892 1338 1784 2230
34 887 1331 1774 2217
35 882 1323 1763 2204
36 877 1315 1753 2191
37 872 1307 1743 2178
38 867 1300 1732 2165
39 862 1292 1722 2152
40 856 1284 1712 2139
41 851 1276 1701 2127
42 846 1269 1691 2114
43 841 1261 1681 2101
44 836 1253 1670 2088
45 831 1245 1660 2075
46 825 1238 1650 2062
47 820 1230 1639 2049
48 815 1222 1629 2036
49 810 1214 1619 2023
50 805 1207 1608 2010
51 800 1199 1598 1997
52 794 1191 1588 1984
53 789 1183 1577 1971
54 784 1176 1567 1958
55 779 1168 1557 1946
56 774 1160 1546 1933
57 769 1152 1536 1920
58 763 1144 1525 1907
59 758 1137 1515 1894
60 753 1129 1505 1881
61 748 1121 1494 1868
62 743 1113 1484 1855
63 737 1105 1473 1842
64 732 1098 1463 1829
65 727 1090 1453 1816
66 722 1082 1442 1803
67 717 1074 1432 1790
68 711 1066 1421 1776
69 706 1059 1411 1763
70 701 1051 1400 1750
71 696 1043 1390 1737
72 690 1035 1380 1724
73 685 1027 1369 1711
74 680 1019 1359 1698
75 675 1012 1348 1685
76 670 1004 1338 1672
77 664 996 1327 1659
78 659 988 1317 1646
79 654 980 1306 1633
80 649 972 1296 1620
81 643 964 1285 1607
82 638 957 1275 1593
83 633 949 1264 1580
84 628 941 1254 1567
85 622 933 1243 1554
86 617 925 1233 1541
87 612 917 1222 1528
88 607 909 1212 1515
89 601 901 1201 1501
90 596 894 1191 1488
91 591 886 1180 1475
92 586 878 1170 1462
93 580 870 1159 1449
94 575 862 1149 1436
95 570 854 1138 1422
96 564 846 1128 1409
97 559 838 1117 1396
98 554 830 1106 1383
99 549 822 1096 1370
100 543 814 1085 1357
101 538 807 1075 1343
102 533 799 1064 1330
103 527 791 1054 1317
104 522 783 1043 1304
105 517 775 1032 1290
106 512 767 1022 1277
107 506 759 1011 1264
108 501 751 1001 1251
109 496 743 990 1237
110 490 735 979 1224
111 485 727 969 1211
112 480 719 958 1198
113 474 711 948 1184
114 469 703 937 1171
115 464 695 926 1158
116 459 687 916 1145
117 453 679 905 1131
118 448 671 894 1118
119 443 663 884 1105
120 437 655 873 1091
121 432 647 862 1078
122 427 639 852 1065
123 421 631 841 1051
124 416 623 831 1038
125 411 615 820 1025
126 405 607 809 1011
127 400 599 798 998
128 395 591 788 985
129 389 583 777 971
130 384 575 766 958
131 379 567 756 945
132 373 559 745 931
133 368 551 734 918
134 362 543 724 904
135 357 535 713 891
136 352 527 702 878
137 346 519 691 864
138 341 511 681 851
139 336 503 670 837
140 330 495 659 824
141 325 487 649 811
142 320 479 638 797
143 314 471 627 784
144 309 463 616 770
145 303 455 606 757
146 298 447 595 743
147 293 438 584 730
148 287 430 573 716
149 282 422 562 703
150 277 414 552 690
(1) VDD = 5 V. Values are bold for each gain's respective trip point range.

7.3.2 VTEMP vs Die Temperature Approximations

The LM26LV's and LM26LV-Q1's VTEMP analog temperature output is very linear. Table 1 and the equation in The Second-Order Equation (Parabolic) represent the most accurate typical performance of the VTEMP voltage output versus temperature.

7.3.2.1 The Second-Order Equation (Parabolic)

The data from Table 1, or Equation 1, when plotted, has an umbrella-shaped parabolic curve. VTEMP is in mV.

Equation 1. LM26LV LM26LV-Q1 20204763.gif

7.3.2.2 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 Equation 2, with the constant and slope in the following set of equations, the best-fit VTEMP versus die temperature performance can be calculated with an approximation error less than 18 mV. VTEMP is in mV.

Equation 2. LM26LV LM26LV-Q1 20204764.gif

7.3.2.3 First-Order Approximation (Linear) Over Small Temperature Range

For a linear approximation, a line can easily be calculated over the desired temperature range from Table 1 using the two-point equation:

Equation 3. LM26LV LM26LV-Q1 20204708.gif

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

For example, to determine the equation of a line with GAIN4, with a temperature from 20°C to 50°C, proceed using Equation 4, Equation 5, and Equation 6:

Equation 4. LM26LV LM26LV-Q1 20204709.gif
Equation 5. V – 2396 mV = –12.8 mV/°C × (T – 20°C)
Equation 6. V = –12.8 mV/°C × (T – 20°C) + 2396 mV

Using this method of linear approximation, the transfer function can be approximated for one or more temperature ranges of interest.

7.3.3 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 deassert 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.

7.3.3.1 OVERTEMP Open-Drain Digital Output

The OVERTEMP active low, open-drain digital output, if used, requires a pullup resistor between this pin and VDD. The following section shows how to determine the pullup resistor value.

7.3.3.1.1 Determining the Pullup Resistor Value

LM26LV LM26LV-Q1 20204752.gif

The pullup resistor value is calculated at the condition of maximum total current, IT, through the resistor. The total current is:

Equation 7. IT = IL + ISINK

where

  • IT is the maximum total current through the pullup resistor at VOL.
  • IL is the load current, which is very low for typical digital inputs.

The pullup resistor maximum value can be found by using Equation 8.

Equation 8. LM26LV LM26LV-Q1 20204754.gif

where

  • VDD(MAX) is the maximum power supply voltage to be used in the customer's system.
  • VOUT is the Voltage at the OVERTEMP pin. Use VOL for calculating the pullup resistor.

7.3.3.1.1.1 Example Calculation

Suppose, for this example, a VDD of 3.3 V ± 0.3 V, a CMOS digital input as a load, a VOL of 0.2 V.

  • For VOL of 0.2 V the electrical specification for OVERTEMP shows a maximum ISINK of 385 µA.
  • Let IL = 1 µA, then IT is about 386 µA maximum. If 35 µA is selected as the current limit then IT for the calculation becomes 35 µA.
  • VDD(MAX) is 3.3 V + 0.3 V = 3.6 V, then calculate the pullup resistor as RPULLUP = (3.6 – 0.2) / 35 µA = 97 kΩ.
  • Based on this calculated value, select the closest resistor value in the tolerance family used.

In this example, if 5% resistor values are used, then the next closest value is 100 kΩ.

7.3.4 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 is at the VTRIP voltage.

If not used, the TRIP_TEST pin may either be left open or grounded.

7.3.5 VTEMP Analog Temperature Sensor Output

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 analog-to-digital converter (ADC). In these applications the source current is required to quickly charge the input capacitor of the ADC. See Application and Implementation for more discussion of this topic. The LM26LV and LM26LV-Q1 are ideal for applications which require strong source or sink current.

7.3.5.1 Noise Considerations

The LM26LV's and LM26LV-Q1's supply-noise rejection (the ratio of the AC signal on VTEMP to the AC signal on VDD) was measured during bench tests. The device's typical attenuation is shown in Typical Characteristics. A load capacitor on the output can help to filter noise.

For operation in very noisy environments, some bypass capacitance must be present on the supply within approximately 2 inches of the LM26LV or LM26LV-Q1.

7.3.5.2 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 20. For capacitive loads greater than 1100 pF, a series resistor is required on the output, as shown in Figure 21, to maintain stable conditions.

LM26LV LM26LV-Q1 20204715.gif Figure 20. LM26LV or LM26LV-Q1 No Decoupling Required for Capacitive Loads Less Than 1100 pF.
LM26LV LM26LV-Q1 20204733.gif Figure 21. LM26LV or LM26LV-Q1 With Series Resistor for Capacitive Loading Greater Than 1100 pF

Table 2. Minimum Series Resistence for Capacitive Loads

CLOAD MINIMUM RS
1.1 nF to 99 nF 3 kΩ
100 nF to 999 nF 1.5 kΩ
1 µF 800 Ω

7.3.5.3 Voltage Shift

The LM26LV and LM26LV-Q1 are 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 V.

This slight shift (a few millivolts) takes place over a wide change (approximately 200 mV) in VDD or VTEMP. Because the shift takes place over a wide temperature change of 5°C to 20°C, VTEMP is always monotonic. The accuracy specifications Accuracy Characteristics already includes this possible shift.

7.4 Device Functional Modes

The LM26LV and LM26LV-Q1 have several modes of operation as detailed in the following drawings.

LM26LV LM26LV-Q1 20204761.gif Figure 22. Temperature Switch Using Push-Pull Output
LM26LV LM26LV-Q1 20204760.gif Figure 24. TRIP_TEST Digital Output Test Circuit
LM26LV LM26LV-Q1 20204762.gif Figure 23. Temperature Switch Using Open-Drain Output

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 Figure 25, 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.

LM26LV LM26LV-Q1 20204765.gif Figure 25. Latch Circuit Using OVERTEMP Output

Alternately, the circuit in Figure 25 the 100 kΩ can be replaced with a short and the momentary reset switch may be removed. In this configuration, when OVERTEMP goes active high, it drives TRIP_TEST high. THRIP TEST high causes OVERTEMP to stay high. It is therefore latched. To release the latch, power down, then power up the LM26LV or LM26LV-Q1. The LM26LV and LM26LV-Q1 always come up in a released condition.