LT1117_02 Datasheet, PDF (5/12 Pages) Linear Technology – 800mA Low Dropout Positive Regulators Adjustable and Fixed 2.85V, 3.3V, 5V

BLOCK DIAGRA
IN
LT1117/LT1117-2.85
LT1117-3.3/LT1117-5
THERMAL
LIMIT
ADJ
OUT
GND
FOR FIXED VOLTAGE DEVICE
LT1117 • BD01
UU
APPLICATIO HI TS
The LT1117 family of 3-terminal regulators are easy to
use. They are protected against short circuit and thermal
overloads. Thermal protection circuitry will shut down the
regulator should the junction temperature exceed 165°C
at the sense point. These regulators are pin compatible
with older 3-terminal adjustable regulators, offer lower
dropout voltage and more precise reference tolerance.
Reference stability over temperature is improved over
older types of regulators.
Stability
The LT1117 family of regulators requires an output ca-
pacitor as part of the device frequency compensation. A
minimum of 10µF of tantalum or 50µF of aluminum
electrolytic is required. The ESR of the output capacitor
should be less than 0.5Ω. Surface mount tantalum capaci-
tors, which have very low ESR, are available from several
manufacturers.
When using the LT1117 adjustable device the adjust
terminal can be bypassed to improve ripple rejection.
When the adjust terminal is bypassed the required value of
the output capacitor increases. The device will require an
output capacitor of 22µF tantalum or 150µF aluminum
electrolytic when the adjust pin is bypassed.
Normally, capacitor values on the order of 100µF are used
in the output of many regulators to ensure good load
transient response with large load current changes. Out-
put capacitance can be increased without limit and larger
values of output capacitance further improve stability and
transient response.
Protection Diodes
In normal operation, the LT1117 family does not need any
protection diodes. Older adjustable regulators required
protection diodes between the adjust pin and the output
and between the output and input to prevent over stress-
ing the die. The internal current paths on the LT1117 adjust
pin are limited by internal resistors. Therefore, even with
capacitors on the adjust pin, no protection diode is needed
to ensure device safety under short-circuit conditions.
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