117IG データシートの表示（PDF） - Microsemi Corporation

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117IG

1.5 AMP THREE TERMINAL ADJUSTABLE VOLTAGE REGULATOR

Microsemi Corporation 

APPLICATION INFORMATION

GENERAL

The SG117A develops a 1.25V reference voltage between the

output and the adjustable terminal (see Figure 1). By placing a

resistor, R1 between these two terminals, a constant current is

caused to flow through R and down through R to set the overall

1

2

output voltage, Normally this current is the specified minimum

load current of 5mA or 10mA.

FIGURE 17 - BASIC REGULATOR CIRCUIT

Because IADJ is very small and constant when compared with the

current through R , it represents a small error and can usually be

1

ignored.

It is easily seen from the above equation, that even if the resistors

were of exact value, the accuracy of the output is limited by the

accuracy of VREF. Earlier adjustable regulators had a reference

tolerance of ±4%. This tolerance is dangerously close to the ±5%

supply tolerance required in many logic and analog systems.

Further, many 1% resistors can drift 0.01%°C adding another 1%

to the output voltage tolerance.

For example, using 2% resistors and ±4% tolerance for VREF,

calculations will show that the expected range of a 5V regulator

design would be 4.66V ≤ VOUT ≤ 5.36V or approximately ±7%. If

the same example were used for a 15V regulator, the expected

tolerance would be ±8%. With these results most applications

require some method of trimming, usually a trim pot. This solution

is expensive and not conducive to volume production.

One of the enhancements of Silicon General’s adjustable regu-

lators over existing devices is tightened initial tolerance. This

allows relatively inexpensive 1% or 2% film resistors to be used

for R1 and R2 while setting output voltage within an acceptable

tolerance range.

With a guaranteed 1% reference, a 5V power supply design,

using ±2% resistors, would have a worse case manufacturing

tolerance of ±4%. If 1% resistors were used, the tolerance would

drop to ±2.5%. A plot of the worst case output voltage tolerance

as a function of resistor tolerance is shown on the front page.

SG117A/SG117 SERIES

For convenience, a table of standard 1% resistor values is shown

below.

Table of ½% and 1% Standard Resistance Values

1.00 1.47 2.15 3.16 4.64 6.81

1.02 1.50 2.21 3.24 4.75 6.98

1.05 1.54 2.26 3.32 4.87 7.15

1.07 1.58 2.32 3.40 4.99 7.32

1.10 1.62 2.37 3.48 5.11 7.50

1.13 1.65 2.43 3.57 5.23 7.68

1.15 1.69 2.49 3.65 5.36 7.87

1.18 1.74 2.55 3.74 5.49 8.06

1.21 1.78 2.61 3.83 5.62 8.25

1.24 1.82 2.67 3.92 5.76 8.45

1.27 1.87 2.74 4.02 5.90 8.66

1.30 1.91 2.80 4.12 6.04 8.87

1.33 1.96 2.87 4.22 6.19 9.09

1.37 2.00 2.94 4.32 6.34 9.31

1.40 2.05 3.01 4.42 6.49 9.53

1.43 2.10 3.09 4.53 6.65 9.76

Standard Resistance Values are obtained from the Decade

Table by multiplying by multiples of 10. As an example:1.21

can represent 1.21Ω, 12.1Ω, 121Ω, 1.21KΩ etc.

FIGURE 18 - CONNECTIONS FOR BEST LOAD REGULATION

FIGURE 19 - 1.2V-25V ADJUSTABLE REGULATOR

2/93 Rev 1.1 2/94

Copyright © 1994

LINFINITY Microelectronics Inc.

6

11861 Western Avenue ∞ Garden Grove, CA 92841

(714) 898-8121 ∞ FAX: (714) 893-2570

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