5

LT1117/LT1117-2.85

LT1117-3.3/LT1117-5

I

DAGRA

BLOCK

APPLICATI

HI TS

The LT1117 family of three-terminal regulators are easy to

use. They are protected against short circuit and thermal

overloads. Thermal protection circuitry will shutdown the

regulator should the junction temperature exceed 165

°C

at the sense point. These regulators are pin compatible

with older three-terminal adjustable regulators, offer

lower dropout voltage and more precise reference toler-

ance. 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 10

µF of tantalum or 50µF of aluminum

electrolytic is required. The ESR of the output capacitor

should be less than 0.5

Ω. 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 22

µF tantalum or 150µF aluminum

electrolytic when the adjust pin is bypassed.

Normally, capacitor values on the order of 100

µF 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. The

LT1117 • BD01

–

+

THERMAL

LIMIT

OUT

IN

ADJ

GND

FOR FIXED VOLTAGE DEVICE