LT1085_15 Datasheet, PDF (10/22 Pages) Linear Technology – 7.5A, 5A, 3A Low Dropout Positive Adjustable Regulators

LT1083/LT1084/LT1085
Block Diagram
V_IN
THERMAL
LIMIT
V_ADJ
V_OUT
1083/4/5 ADJ BD
Applications Information
The LT1083 family of 3-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 3-terminal
adjustable devices, 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 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
a 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 coefficient.
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
capacitors 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
OUTPUT
10µF
10µF Tantalum, 50µF Aluminum
10µF
22µF Tantalum, 150µF Aluminum
ADJUSTMENT
None
20µF
10
For more information www.linear.com/LT1083
108345fh