LM93CIMT National Semiconductor, LM93CIMT Datasheet - Page 14

• Manufacturer Part Number: LM93CIMT
• Description: Microprocessor Support IC
• Manufacturer: National Semiconductor

Specifications of LM93CIMT

• Peak Reflow Compatible (260 C): No
• Supply Voltage Max: 3.6V
• Leaded Process Compatible: No
• Supply Voltage Min: 3V
• Operating Temperature Min: 0��C
• Package / Case: 56-TSSOP
• Operating Temperature Max: 85°C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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12.0 Functional Description
The +3.3V standby voltage is used as a reference for the
level shifting. Therefore, the tolerance of this voltage directly
effects the accuracy of the −12V reading. To minimize ratio
errors, a tolerance of better than
recommended that the equivalent thevenin resistance of the
divider is between 1k and 7k to minimize errors caused by
leakage currents at extreme temperatures. To calculate the
ratio of R1 to R2 use this equation:
where V
reference voltage of +3.3V and AD_IN is the voltage required
at the AD input for a
Therefore, for this case:
Using standard 1% resistor values for R1 of 5.76 kΩ and R2
of 1.4 kΩ yields an R1 to R2 ratio of 4.1143.
The input voltage V
register reading (VR) using this equation:
The table below summarizes the theoretical voltage values
for value register readings near −12V.
(Continued)
Value Register
IN
15
16
17
18
19
20
21
22
23
24
25
26
is the nominal input voltage of −12V, V
Required External Level Shifting
Resistors for −12V Power Input
IN
1
⁄
4
can be calculated using the value
scale reading or 0.309V.
-13.2068
-13.1821
-13.1574
-13.1327
-13.1080
-13.0833
-13.0586
-13.0339
-13.0092
-12.9845
-12.9598
-12.9351
V
IN
±
1% should be used. It is
20068210
% ∆ from −12V
-10.0563
-9.8505
-9.6448
-9.4390
-9.2332
-9.0275
-8.8217
-8.6159
-8.4101
-8.2044
-7.9986
-7.7928
REF
is the
14
Value Register
27
28
29
30
31
32
33
34
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
-12.9104
-12.8858
-12.8611
-12.8364
-12.8117
-12.7870
-12.7623
-12.7376
-12.7129
-12.6882
-12.6635
-12.6388
-12.6141
-12.5894
-12.5648
-12.5401
-12.5154
-12.4907
-12.4660
-12.4413
-12.4166
-12.3919
-12.3672
-12.3425
-12.3178
-12.2931
-12.2684
-12.2438
-12.2191
-12.1944
-12.1697
-12.1450
-12.1203
-12.0956
-12.0709
-12.0462
-12.0215
-11.9968
-11.9721
-11.9474
-11.9228
-11.8981
-11.8734
-11.8487
-11.8240
-11.7993
-11.7746
-11.7499
-11.7252
-11.7005
V
IN
% ∆ from −12V
-7.5871
-7.3813
-7.1755
-6.9698
-6.7640
-6.5582
-6.3524
-6.1467
-5.9409
-5.7351
-5.5294
-5.3236
-4.9121
-4.7063
-4.5005
-4.2947
-4.0890
-3.8832
-3.6774
-3.4717
-3.2659
-3.0601
-2.8544
-2.6486
-2.4428
-2.2370
-2.0313
-1.8255
-1.6197
-1.4140
-1.2082
-1.0024
-0.7967
-0.5909
-0.3851
-0.1793
-5.1178
0.0264
0.2322
0.4380
0.6437
0.8495
1.0553
1.2610
1.4668
1.6726
1.8784
2.0841
2.2899
2.4957