NSC LM94021BIMGX

LM94021
Multi-Gain Analog Temperature Sensor
General Description
The LM94021 is a precision analog output CMOS
integrated-circuit temperature sensor that operates at a supply voltage as low as 1.5V. While operating over the wide
temperature range of −50˚C to +150˚C, the LM94021 delivers an output voltage that is inversely porportional to measured temperature. The LM94021’s low supply current
makes it ideal for battery-powered systems as well as general temperature sensing applications.
Two logic inputs, Gain Select 1 (GS1) and Gain Select 0
(GS0), select the gain of the temperature-to-voltage output
transfer function. Four slopes are selectable: −5.5 mV/˚C,
−8.2 mV/˚C, −10.9 mV/˚C, and −13.6 mV/˚C. In the lowest
gain configuration (GS1 and GS0 both tied low), the
LM94021 can operate with a 1.5V supply while measuring
temperature over the full −50˚C to +150˚C operating range.
Tying both inputs high causes the transfer function to have
the largest gain of −13.6 mV/˚C for maximum temperature
sensitivity. The gain-select inputs can be tied directly to VDD
or Ground without any pull-up or pull-down resistors, reducing component count and board area. These inputs can also
be driven by logic signals allowing the system to optimize the
gain during operation or system diagnostics.
Applications
n
n
n
n
n Disk Drives
n Games
n Appliances
Features
n Low 1.5V operation
n Four selectable gains
n Very accurate over wide temperature range of −50˚C to
+150˚C
n Low quiescent current
n Output is short-circuit protected
n Extremely small SC70 package
n Footprint compatible with the industry-standard LM20
temperature sensor
Key Specifications
j Supply Voltage
j Temperature
Accuracy
j Operating
Temperature
Cell phones
Wireless Transceivers
Battery Management
Automotive
Connection Diagram
1.5V to 5.5V
j Supply Current
9 µA (typ)
± 1.5˚C
± 1.8˚C
± 2.1˚C
± 2.7˚C
20˚C to 40˚C
-50˚C to 70˚C
-50˚C to 90˚C
-50˚C to 150˚C
−50˚C to 150˚C
Typical Transfer Characteristic
SC70-5
Output Voltage vs Temperature
20108601
Top View
See NS Package Number MAA05A
20108624
© 2005 National Semiconductor Corporation
DS201086
www.national.com
LM94021 Multi-Gain Analog Temperature Sensor
February 2005
LM94021
Typical Application
Full-Range Celsius Temperature Sensor (−50˚C to +150˚C)
Operating from a Single Battery Cell
20108602
Ordering Information
Order
Temperature
NS Package
Device
Number
Accuracy
Number
Marking
Transport Media
± 1.5˚C to ± 2.7˚C
± 1.5˚C to ± 2.7˚C
MAA05A
21B
3000 Units on Tape and Reel
MAA05A
21B
9000 Units on Tape and Reel
LM94021BIMG
LM94021BIMGX
Pin Descriptions
Label
Pin
Number
Type
Equivalent Circuit
Function
GS1
5
Logic
Input
Gain Select 1 - One of two inputs for selecting
the slope of the output response
GS0
1
Logic
Input
Gain Select 0 - One of two inputs for selecting
the slope of the output response
OUT
3
Analog
Output
Outputs a voltage which is inversely
proportional to temperature
VDD
4
Power
Positive Supply Voltage
GND
2
Ground
Power Supply Ground
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2
Supply Voltage
Machine Model
Soldering process must comply with National’s
Reflow Temperature Profile specifications. Refer to
www.national.com/packaging. (Note 4)
−0.2V to +6.0V
Voltage at Output Pin
−0.2V to (VDD + 0.5V)
± 7 mA
Output Current
Voltage at GS0 and GS1 Input
Pins
Storage Temperature
Operating Ratings(Note 1)
−0.2V to +6.0V
Input Current at any pin (Note 2)
5 mA
Specified Temperature Range:
−65˚C to +150˚C
Maximum Junction Temperature
(TJMAX)
Supply Voltage Range (VDD)
+150˚C
TMIN ≤ TA ≤ TMAX
−50˚C ≤ TA ≤ +150˚C
LM94021
+1.5 V to +5.5 V
Thermal Resistance (θJA) (Note 5)
SC-70
ESD Susceptibility (Note 3) :
Human Body Model
250V
415˚C/W
2500V
Accuracy Characteristics
These limits do not include DC load regulation. These stated accuracy limits are with reference to the values in the LM94021
Transfer Table.
Parameter
Temperature
Error
(Note 8)
Conditions
GS1=0
GS0=0
TA = +20˚C to +40˚C; VDD = 1.5V to 5.5V
TA = +0˚C to +70˚C; VDD = 1.5V to 5.5V
TA = +0˚C to +90˚C; VDD = 1.5V to 5.5V
TA = +0˚C to +120˚C; VDD = 1.5V to 5.5V
TA = +0˚C to +150˚C; VDD = 1.5V to 5.5V
TA = −50˚C to +0˚C; VDD = 1.6V to 5.5V
GS1=0
GS0=1
TA = +20˚C to +40˚C; VDD = 1.8V to 5.5V
TA = +0˚C to +70˚C; VDD = 1.9V to 5.5V
TA = +0˚C to +90˚C; VDD = 1.9V to 5.5V
TA = +0˚C to +120˚C; VDD = 1.9V to 5.5V
TA = +0˚C to +150˚C; VDD = 1.9V to 5.5V
TA = −50˚C to +0˚C; VDD = 2.3V to 5.5V
GS1=1
GS0=0
TA = +20˚C to +40˚C; VDD = 2.2V to 5.5V
TA = +0˚C to +70˚C; VDD = 2.4V to 5.5V
TA = +0˚C to +90˚C; VDD = 2.4V to 5.5V
TA = +0˚C to +120˚C; VDD = 2.4V to 5.5V
TA = +0˚C to +150˚C; VDD = 2.4V to 5.5V
TA = −50˚C to +0˚C; VDD = 3.0V to 5.5V
GS1=1
GS0=1
TA = +20˚C to +40˚C; VDD = 2.7V to 5.5V
TA = +0˚C to +70˚C; VDD = 3.0V to 5.5V
TA = +0˚C to +90˚C; VDD = 3.0V to 5.5V
TA = +0˚C to +120˚C; VDD = 3.0V to 5.5V
TA = 0˚C to +150˚C; VDD = 3.0V to 5.5V
TA = −50˚C to +0˚C; VDD = 3.6V to 5.5V
3
Limits
(Note
7)
Units
(Limit)
± 1.5
± 1.8
± 2.1
± 2.4
± 2.7
± 1.8
± 1.5
± 1.8
± 2.1
± 2.4
± 2.7
± 1.8
± 1.5
± 1.8
± 2.1
± 2.4
± 2.7
± 1.8
± 1.5
± 1.8
± 2.1
± 2.4
± 2.7
± 1.8
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
˚C (max)
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LM94021
Absolute Maximum Ratings (Note 1)
LM94021
Electrical Characteristics
Unless otherwise noted, these specifications apply for +VDD = +1.5V to +5.5V . Boldface limits apply for TA = TJ = TMIN to
TMAX ; all other limits TA = TJ = 25˚C.
Symbol
Parameter
Conditions
0,
0,
1,
1,
GS0
GS1
GS0
GS0
=
=
=
=
0
1
0
1
Limits (Note 7)
Units
(Limit)
Sensor Gain
GS1
GS1
GS1
GS1
Load Regulation
(Note 10)
Source ≤ 2.0 µA (Note 11)
Sink ≤ 100 µA
Sink = 50 µA
0.4
mV (max)
mV (max)
mV
Line Regulation (Note
14)
(VDD - VOUT) ≥ 200 mV
200
µV/V
IS
Supply Current
TA = +30˚C to +150˚C
TA = -50˚C to +150˚C
9
CL
Output Load
Capacitance
Power-on Time
(Note 12)
=
=
=
=
Typical
(Note 6)
-5.5
-8.2
-10.9
-13.6
mV/˚C
mV/˚C
mV/˚C
mV/˚C
-1
1.6
12
13
1100
pF (max)
0.7
0.8
CL= 0 pF
CL=1100 pF
µA (max)
µA (max)
5
10
ms (max)
ms (max)
VIH
GS1 and GS0 Input
Logic "1" Threshold
Voltage
VDD- 0.5V
V (min)
VIL
GS1 and GS0 Input
Logic "0" Threshold
Voltage
0.5
V (max)
IIH
Logic "1" Input Current
(Note 13)
0.001
1
µA (max)
IIL
Logic "0" Input Current
(Note 13)
0.001
1
µA (max)
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 > V+), the current at that pin should be limited to 5 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin.
Note 4: Reflow temperature profiles are different for lead-free and non-lead-free packages.
Note 5: The junction to ambient thermal resistance (θJA) is specified without a heat sink in still air.
Note 6: Typicals are at TJ = TA = 25˚C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Accuracy is defined as the error between the measured and reference output voltages, tabulated in the Transfer 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 9: Changes in output due to self heating can be computed by multiplying the internal dissipation by the thermal resistance.
Note 10: Source currents are flowing out of the LM94021. Sink currents are flowing into the LM94021.
Note 11: Assumes (VDD - VOUT) ^ 200mV.
Note 12: Guaranteed by design.
Note 13: The input current is leakage only and is highest at high temperature. It is typically only 0.001µA. The 1µA limit is solely based on a testing limitation and
does not reflect the actual performance of the part.
Note 14: Line regulation is calculated by subtracting the output voltage at the highest supply voltage from the output voltage at the lowest supply voltage. The typical
line regulation specification does not include the output voltage shift discussed in Section 5.0.
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4
Temperature Error vs. Temperature
Minimum Operating Temperature vs. Supply Voltage
20108607
20108606
Supply Current vs. Temperature
Supply Current vs. Supply Voltage
20108604
20108605
Load Regulation, Sourcing Current
Load Regulation, Sinking Current
20108640
20108641
5
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LM94021
Typical Performance Characteristics
LM94021
Typical Performance Characteristics
(Continued)
Output Voltage vs. Supply Voltage
Gain Select = 00
Change in Vout vs. Overhead Voltage
20108642
20108634
Output Voltage vs. Supply Voltage
Gain Select = 01
Output Voltage vs. Supply Voltage
Gain Select = 10
20108635
20108636
Output Voltage vs. Supply Voltage
Gain Select = 11
20108637
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6
The output voltages in this table apply for VDD = 5V.
The LM94021 has four selectable gains, each of which can
be selected by the GS1 and GS0 input pins. The output
voltage for each gain, across the complete operating temperature range is shown in the LM94021 Transfer Table,
below. This table is the reference from which the LM94021
accuracy specifications (listed in the Electrical Characteristics section) are determined. This table can be used, for
example, in a host processor look-up table. A file containing
this data is available for download at www.national.com/
appinfo/tempsensors.
Temperature
(˚C)
GS = 00
(mV)
GS = 01
(mV)
GS = 10
(mV)
GS = 11
(mV)
-13
1104
1671
2239
2807
-12
1098
1663
2228
2793
-11
1093
1656
2218
2780
-10
1088
1648
2207
2767
-9
1082
1639
2197
2754
-8
1077
1631
2186
2740
-7
1072
1623
2175
2727
-6
1066
1615
2164
2714
-5
1061
1607
2154
2700
-4
1055
1599
2143
2687
-3
1050
1591
2132
2674
-2
1044
1583
2122
2660
-1
1039
1575
2111
2647
0
1034
1567
2100
2633
1
1028
1559
2089
2620
2
1023
1551
2079
2607
3
1017
1543
2068
2593
4
1012
1535
2057
2580
5
1007
1527
2047
2567
6
1001
1519
2036
2553
7
996
1511
2025
2540
8
990
1502
2014
2527
9
985
1494
2004
2513
10
980
1486
1993
2500
11
974
1478
1982
2486
12
969
1470
1971
2473
13
963
1462
1961
2459
14
958
1454
1950
2446
15
952
1446
1939
2433
16
947
1438
1928
2419
17
941
1430
1918
2406
18
936
1421
1907
2392
19
931
1413
1896
2379
20
925
1405
1885
2365
21
920
1397
1874
2352
22
914
1389
1864
2338
23
909
1381
1853
2325
24
903
1373
1842
2311
25
898
1365
1831
2298
26
892
1356
1820
2285
27
887
1348
1810
2271
28
882
1340
1799
2258
29
876
1332
1788
2244
30
871
1324
1777
2231
31
865
1316
1766
2217
32
860
1308
1756
2204
33
854
1299
1745
2190
34
849
1291
1734
2176
35
843
1283
1723
2163
LM94021 Transfer Table
The output voltages in this table apply for VDD = 5V.
Temperature
(˚C)
GS = 00
(mV)
GS = 01
(mV)
GS = 10
(mV)
GS = 11
(mV)
-50
1299
1955
2616
3277
-49
1294
1949
2607
3266
-48
1289
1942
2598
3254
-47
1284
1935
2589
3243
-46
1278
1928
2580
3232
-45
1273
1921
2571
3221
-44
1268
1915
2562
3210
-43
1263
1908
2553
3199
-42
1257
1900
2543
3186
-41
1252
1892
2533
3173
-40
1247
1885
2522
3160
-39
1242
1877
2512
3147
-38
1236
1869
2501
3134
-37
1231
1861
2491
3121
-36
1226
1853
2481
3108
-35
1221
1845
2470
3095
-34
1215
1838
2460
3082
-33
1210
1830
2449
3069
-32
1205
1822
2439
3056
-31
1200
1814
2429
3043
-30
1194
1806
2418
3030
-29
1189
1798
2408
3017
-28
1184
1790
2397
3004
-27
1178
1783
2387
2991
-26
1173
1775
2376
2978
-25
1168
1767
2366
2965
-24
1162
1759
2355
2952
-23
1157
1751
2345
2938
-22
1152
1743
2334
2925
-21
1146
1735
2324
2912
-20
1141
1727
2313
2899
-19
1136
1719
2302
2886
-18
1130
1711
2292
2873
-17
1125
1703
2281
2859
-16
1120
1695
2271
2846
-15
1114
1687
2260
2833
-14
1109
1679
2250
2820
7
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LM94021
1.0 LM94021 Transfer Function
LM94021
1.0 LM94021 Transfer Function
The output voltages in this table apply for VDD = 5V.
Temperature
(˚C)
GS = 00
(mV)
GS = 01
(mV)
GS = 10
(mV)
GS = 11
(mV)
(Continued)
The output voltages in this table apply for VDD = 5V.
81
585
898
1212
1525
82
579
890
1201
1511
Temperature
(˚C)
GS = 00
(mV)
GS = 01
(mV)
GS = 10
(mV)
GS = 11
(mV)
83
574
881
1189
1497
36
838
1275
1712
2149
84
568
873
1178
1483
37
832
1267
1701
2136
85
562
865
1167
1469
38
827
1258
1690
2122
86
557
856
1155
1455
39
821
1250
1679
2108
87
551
848
1144
1441
40
816
1242
1668
2095
88
545
839
1133
1427
41
810
1234
1657
2081
89
539
831
1122
1413
42
804
1225
1646
2067
90
534
822
1110
1399
43
799
1217
1635
2054
91
528
814
1099
1385
44
793
1209
1624
2040
92
522
805
1088
1371
45
788
1201
1613
2026
93
517
797
1076
1356
46
782
1192
1602
2012
94
511
788
1065
1342
47
777
1184
1591
1999
95
505
779
1054
1328
48
771
1176
1580
1985
96
499
771
1042
1314
49
766
1167
1569
1971
97
494
762
1031
1300
50
760
1159
1558
1958
98
488
754
1020
1286
51
754
1151
1547
1944
99
482
745
1008
1272
52
749
1143
1536
1930
100
476
737
997
1257
53
743
1134
1525
1916
101
471
728
986
1243
54
738
1126
1514
1902
102
465
720
974
1229
55
732
1118
1503
1888
103
459
711
963
1215
56
726
1109
1492
1875
104
453
702
951
1201
57
721
1101
1481
1861
105
448
694
940
1186
58
715
1093
1470
1847
106
442
685
929
1172
59
710
1084
1459
1833
107
436
677
917
1158
60
704
1076
1448
1819
108
430
668
906
1144
61
698
1067
1436
1805
109
425
660
895
1130
62
693
1059
1425
1791
110
419
651
883
1115
63
687
1051
1414
1777
111
413
642
872
1101
64
681
1042
1403
1763
112
407
634
860
1087
65
676
1034
1391
1749
113
401
625
849
1073
66
670
1025
1380
1735
114
396
617
837
1058
67
664
1017
1369
1721
115
390
608
826
1044
68
659
1008
1358
1707
116
384
599
814
1030
69
653
1000
1346
1693
117
378
591
803
1015
70
647
991
1335
1679
118
372
582
791
1001
71
642
983
1324
1665
119
367
573
780
987
72
636
974
1313
1651
120
361
565
769
973
73
630
966
1301
1637
121
355
556
757
958
74
625
957
1290
1623
122
349
547
745
944
75
619
949
1279
1609
123
343
539
734
929
76
613
941
1268
1595
124
337
530
722
915
77
608
932
1257
1581
125
332
521
711
901
78
602
924
1245
1567
126
326
513
699
886
79
596
915
1234
1553
127
320
504
688
872
80
591
907
1223
1539
128
314
495
676
858
129
308
487
665
843
(Continued)
LM94021 Transfer Table
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8
Although the LM94021 is very linear, its response does have
a slight downward parabolic shape. This shape is very accurately reflected in the LM94021 Transfer Table. For a
linear approximation, a line can easily be calculated over the
desired temperature range from the Table using the twopoint equation:
(Continued)
LM94021 Transfer Table
(Continued)
The output voltages in this table apply for VDD = 5V.
Temperature
(˚C)
GS = 00
(mV)
GS = 01
(mV)
GS = 10
(mV)
GS = 11
(mV)
130
302
478
653
829
131
296
469
642
814
132
291
460
630
800
133
285
452
618
786
134
279
443
607
771
135
273
434
595
757
136
267
425
584
742
137
261
416
572
728
138
255
408
560
713
139
249
399
549
699
140
243
390
537
684
141
237
381
525
670
142
231
372
514
655
143
225
363
502
640
144
219
354
490
626
145
213
346
479
611
146
207
337
467
597
147
201
328
455
582
148
195
319
443
568
149
189
310
432
553
150
183
301
420
538
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, if we want to determine the equation of a line
with the Gain Setting at GS1 = 0 and GS0 = 0, over a
temperature range of 20˚C to 50˚C, we would proceed as
follows:
Using this method of linear approximation, the transfer function can be approximated for one or more temperature
ranges of interest.
9
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LM94021
1.0 LM94021 Transfer Function
LM94021
2.0 Mounting and Thermal
Conductivity
4.0 Capacitive Loads
The LM94021 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 LM94021 can drive a capacitive load less than or equal
to 1100 pF as shown in Figure 2. For capacitive loads
greater than 1100 pF, a series resistor may be required on
the output, as shown in Figure 3.
The LM94021 can be applied easily in the same way as
other integrated-circuit temperature sensors. It can be glued
or cemented to a surface.
To ensure good thermal conductivity, the backside of the
LM94021 die is directly attached to the GND pin (Pin 2). The
temperatures of the lands and traces to the other leads of the
LM94021 will also affect the temperature reading.
Alternatively, the LM94021 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
LM94021 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 output to ground or VDD, the output
from the LM94021 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 LM94021’s die temperature is
20108615
FIGURE 2. LM94021 No Decoupling Required for
Capacitive Loads Less than 1100 pF.
where TA is the ambient temperature, IQ is the quiescent
current, ILis 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 Select = 11, VOUT = 2.231
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
LM94021’s junction temperature is the actual temperature
being measured, care should be taken to minimize the load
current that the LM94021 is required to drive. Figure 1 shows
the thermal resistance of the LM94021.
Device Number
NS Package
Number
Thermal
Resistance (θJA)
LM94021BIMG
MAA05A
415˚C/W
20108633
CLOAD
RS
1.1 nF to
99 nF
3 kΩ
100 nF to
999 nF
1.5 kΩ
1 µF
800 Ω
FIGURE 3. LM94021 with series resistor for capacitive
Loading greater than 1100 pF.
FIGURE 1. LM94021 Thermal Resistance
5.0 Output Voltage Shift
3.0 Noise Considerations
The LM94021 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 VOUT. The shift typically occurs
when VDD- VOUT = 1.0V.
This slight shift (a few millivolts) takes place over a wide
change (approximately 200 mV) in VDD or VOUT. Since the
shift takes place over a wide temperature change of 5˚C to
20˚C, VOUT is always monotonic. The accuracy specifications in the Electrical Characteristics table already include
this possible shift.
The LM94021 has excellent noise rejection (the ratio of the
AC signal on VOUT to the AC signal on VDD). During bench
tests, sine wave rejection of -54 dB or better was observed
over 200 Hz to 10 kHz; Also, -28 dB or better was observed
from 10 kHz to 1 MHz. A load capacitor on the output can
help filter noise; for example, a 1 nF load capacitor resulted
in -51 dB or better from 200 Hz to 1 MHz.
There is no specific requirement for the use of a bypass
capacitor close to the LM94021 because it does not draw
transient currents. For operation in very noisy environments,
some bypass capacitance may be required. The capacitance
does not need to be in close proximity to the LM94021. The
LM94021 has been bench tested successfully with a bypass
capacitor as far as 6 inches away. In fact, it can be powered
by a properly-bypassed logic gate.
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10
noise (for example, noise coupling on the output line or
quantization noise induced by an analog-to-digital converter
which may be sampling the LM94021 output).
The Gain Select digital inputs can be tied to the rails or can
be driven from digital outputs such as microcontroller GPIO
pins. In low-supply voltage applications, the ability to reduce
the gain to -5.5 mV/˚C allows the LM94021 to operate over
the full -50 ˚C to 150 ˚C range. When a larger supply voltage
is present, the gain can be increased as high as -13.6
mV/˚C. The larger gain is optimal for reducing the effects of
Another application advantage of the digitally selectable gain
is the ability to perform dynamic testing of the LM94021
while it is running in a system. By toggling the logic levels of
the gain select pins and monitoring the resultant change in
the output voltage level, the host system can verify the
functionality of the LM94021.
11
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LM94021
6.0 Selectable Gain for
Optimization and In Situ Testing
LM94021
7.0 Applications Circuits
20108618
FIGURE 4. Celsius Thermostat
20108619
FIGURE 5. Conserving Power Dissipation with Shutdown
20108628
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 LM94021 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
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12
LM94021 Multi-Gain Analog Temperature Sensor
Physical Dimensions
inches (millimeters) unless otherwise noted
5-Lead SC70 Molded Package
Order Number LM94021BIMG, LM94021BIMGX
NS Package Number MAA05A
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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