LT1083/LT1084/LT1085 Fixed
9
1083ffe
For more information www.linear.com/LT1083
THERMAL
LIMIT
GND
V
OUT
LT1083/4/5 BD
V
IN
–
+
block DiagraM
applicaTions inForMaTion
The LT1083 family of three-terminal regulators are easy
to use and have all the protection features that are ex-
pected in high performance voltage regulators. They are
short
circuit protected,
have safe area protection as well
as thermal shutdown to turn off the regulator should the
temperature exceed about 165°C.
These regulators offer lower dropout voltage and more
precise reference tolerance. Further, the reference stability
with temperature is improved over older types of regula
-
tors. The only circuit difference between using the LT1083
family and older regulators is that they require 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 aluminum 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
characteristics are available. These capacitors differ in
capacitor tolerance (sometimes ranging up to ±100%),
equivalent series resistance, and capacitance temperature
coefficient. The 150µF or 22µF values given will ensure
stability.
Normally, capacitor values on the order of 100µF are used
in the output of many regulators to ensure good transient
response with heavy load current changes. Output capaci
-
tance can be increased without limit and larger values of
output capacitance further improve stability and transient
response of the LT1083 regulators.
Another possible stability problem that can occur in mono-
lithic IC regulators is current limit oscillations. These can
occur because in current limit the safe area protection
exhibits a negative impedance. The safe area protection
decreases the current limit as the input-to-output volt
-
age increases.That is the equivalent of having a negative
