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Dec.2015 - Rev. A
© 2015 ROHM Co., Ltd. All rights reserved.
Linear Regulator Series
Linear Regulator Specifications
A linear regulator data sheet includes a specifications table
that lists output voltage values and precision. Besides, very
important information such as maximum ratings, operating
conditions and characteristic graphs are described in the
table.
The absolute maximum rating is defined as a value that must
not be exceeded even for a moment. Although some items
are defined by a time component, such as short-circuit time, it
is basically prohibited to exceed the absolute maximum rating
in every case. And, for obvious reasons, a tolerance like
±10% is never assigned to values. We sometimes receive
questions like: What will happen if a value exceeds the
absolute maximum rating? How much margin does the
system have? (These questions may be just a matter of
interest.) However, they miss the point when it comes to
considering the purpose of absolute maximum rating. You
should make efforts so that the operating maximum value will
not exceed the maximum rating or try to use a linear regulator
model having the maximum rating that allows the operating
maximum value.
It is important to identify the conditions that guarantee the
specification values, for example, applied voltage and
temperature. Actual use conditions do not always accord
with specification-stipulated conditions. As a typical
example, if a condition of Ta=25°C is given, its guaranteed
value persistently is a value at Ta=25°C. However, in actual
use, a constant condition at Ta=25°C would be possible only
in a thermostatic bath. Therefore, in examining the
specification value, it is necessary to verify whether the value
applies to a single specific condition or a range of conditions,
for example, a range of operating temperatures, and to
confirm the value in a condition close to the actual use
condition and operating condition of the designed equipment.
To do this, a supplemental reference graph is often useful.
Lastly, the specification values include descriptions of any
one or all of the minimum values (Min), maximum values
(Max) and typical values (Typ). Among these, only the
minimum value and maximum value are guaranteed. The
typical value (Typ) is “an approximate value” based on
characteristic distributions and statistical techniques.
Basically, every product is designed based on the
specification values. Then, which value should we use to
design products? Although general designs might be based
on typical values in principle, the design should be based on
the values that pose the worst conditions. This selection
depends on the know-how and experience of designers
themselves.
This paper explains typical items in linear regulator
specifications. However, other specification items may not
be ignored. Reading a data sheet carefully is very important
for designers, not only for linear regulators but also for other
equipment.
No.15020EAY18
A
pplication Note
2/12
www.rohm.com
Dec.2015 - Rev. A
© 2015 ROHM Co., Ltd. All rights reserved.
Linear Regulator Specifications
Table of Contents
1. Input Power Supply Voltage Range ................................................................... 3
2. Output Voltage Range ........................................................................................ 3
3. Output Voltage Precision .................................................................................... 4
4. Output Current ................................................................................................... 4
5. Input/Output Voltage Difference ......................................................................... 4
6. Transient Response Characteristics ................................................................... 5
7. Ripple Rejection Ratio ........................................................................................ 6
8. Circuit Current .................................................................................................... 7
9. EN Pin (CTL/STBY Pin) ..................................................................................... 8
10. Line regulation ................................................................................................. 9
11. Load Regulation ............................................................................................... 9
12. Output Discharge ............................................................................................. 9
13. Soft Start ........................................................................................................ 10
14. Input Capacitor ............................................................................................... 10
15. Output Capacitor ............................................................................................ 10
16. Power Dissipation .......................................................................................... 11
17. Overcurrent Protection ................................................................................... 11
18. Thermal Shut Down ....................................................................................... 12