LM1117IMPX-3.3 National Semiconductor, LM1117IMPX-3.3 Datasheet - Page 2

• Manufacturer Part Number: LM1117IMPX-3.3
• Description: IC,VOLT REGULATOR,FIXED,+3.3V,BIPOLAR,SOT-223,3PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM1117IMPX-3.3

• Rohs Compliant: NO

www.national.com
The Worst Case Approach
The overly conservative approach to this problem is to take
the known relationship between reference voltage toler-
ances and output voltage and calculate the worst case out-
put voltage that can occur in the unlikely case that all toler-
ances are simultaneously at their worst case extremes.
Remember that exact values for the desired R1 and R2 may
not be available so an additional, but static, voltage error
may have to be tolerated.
Equations 2 and 3 are commonly applied using plus and
minus 1% for values of R
approach is that it results in excessively conservative toler-
ance limits. We will show later that this is especially true
since V
Results for the worst case approach are tabulated in Table 1.
The minimum and maximum deviations are not exactly sym-
∆V
∆V
∆V
±
±
±
±
±
±
±
±
±
±
±
±
ref
ref
ref
ref
0.5
1.0
2.0
5.0
0.5
1.0
2.0
5.0
0.5
1.0
2.0
5.0
[%]
[%]
[%]
, R1, and R2 are uncorrelated random variables.
∆V
∆V
∆V
0.5%
0.5%
0.5%
0.82
1.32
2.32
5.33
1.13
1.64
2.64
2.64
1.41
1.91
2.92
5.95
out
out
out
TABLE 1. Values of Worst Case Error [%] for Common V
min
[%]
[%]
[%]
V
V
V
out
out
out
and R
Resistor Tolerance
Resistor Tolerance
Resistor Tolerance
= 1.8 V
= 3.3 V
= 12 V
max
∆V
∆V
∆V
1.14
1.65
2.65
5.67
1.77
2.28
3.29
6.33
2.32
2.83
3.85
6.90
. The drawback of this
out
out
out
1%
1%
1%
[%]
[%]
[%]
∆V
∆V
∆V
11.93
10.54
11.64
14.92
3.85
4.37
5.40
8.50
7.14
7.67
8.73
9.99
out
out
out
5%
5%
5%
[%]
[%]
[%]
2
∆V
∆V
∆V
metric so only the worst case is tabulated. The worst case
always occurs on the maximum side. Centering of the nomi-
nal value at the actual mean can take advantage of this fact
and gain a small improvement in worst case tolerancing.
±
±
±
±
±
±
±
±
±
±
±
±
ref
ref
ref
0.5
1.0
2.0
5.0
0.5
1.0
2.0
5.0
0.5
1.0
2.0
5.0
[%]
[%]
[%]
∆V
∆V
∆V
out
0.5%
0.5%
0.5%
1.01
1.52
2.52
5.54
1.26
1.77
2.77
5.80
1.43
1.93
2.94
5.97
out
out
out
’s (V
[%]
[%]
[%]
V
V
V
out
out
ref
out
Resistor Tolerance
Resistor Tolerance
Resistor Tolerance
= 1.275 V)
= 2.5 V
= 5.0 V
= 15 V
∆V
∆V
∆V
1.53
2.04
3.05
6.08
2.03
2.54
3.55
6.60
2.36
2.87
3.89
6.95
out
out
out
1%
1%
1%
[%]
[%]
[%]
∆V
∆V
∆V
10.61
10.10
13.33
10.21
10.76
11.86
15.15
5.87
6.40
7.45
8.48
9.02
out
out
out
5%
5%
5%
[%]
[%]
[%]
(2)
(3)