LT1083/LT1084/LT1085
BLOCK DIAGRAM
V
ADJ
APPLICATIONS INFORMATION
The LT1083 family of three-terminal adjustable regulators
is easy to use and has all the protection features that are
expected in high performance voltage regulators. They are
short-circuit protected, and have safe area protection as
well as thermal shutdown to turn off the regulator should
the junction temperature exceed about 165°C.
These regulators are pin compatible with older three-
terminal adjustable devices, offer lower dropout voltage
and more precise reference tolerance. Further, the refer-
ence stability with temperature is improved over older
types of regulators. The only circuit difference between
using the LT1083 family and older regulators is that this
new family requires an output capacitor for stability.
Stability
The circuit design used in the LT1083 family requires the
use of an output capacitor as part of the device frequency
compensation. For all operating conditions, the addition of
150µF aluminium electrolytic or a 22µF solid tantalum on
the output will ensure stability. Normally, capacitors much
smaller than this can be used with the LT1083. Many
different types of capacitors with widely varying charac-
teristics are available. These capacitors differ in capacitor
tolerance (sometimes ranging up to
±100%),
equivalent
series resistance, and capacitance temperature coeffi-
cient. The 150µF or 22µF values given will ensure stability.
When the adjustment terminal is bypassed to improve the
ripple rejection, the requirement for an output capacitor
increases. The value of 22µF tantalum or 150µF aluminum
covers all cases of bypassing the adjustment terminal.
Without bypassing the adjustment terminal, smaller ca-
pacitors can be used with equally good results and the
table below shows approximately what size capacitors are
needed to ensure stability.
Recommended Capacitor Values
INPUT
10µF
10µF
OUTPUT
10µF Tantalum, 50µF Aluminum
22µF Tantalum, 150µF Aluminum
ADJUSTMENT
None
20µF
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1083/4/5 ADJ BD
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LINER [ LINEAR TECHNOLOGY ]
