Datasheet LT1117, LT1117-2.85, LT1117-3.3, LT1117-5 (Analog Devices) - 7

LT1117/LT1117-2.85 LT1117-3.3/LT1117-5
APPLICATIONS INFORMATION
The LT1117 family of 3-terminal regulators are easy to
Protection Diodes
use. They are protected against short circuit and thermal In normal operation, the LT1117 family does not need any overloads. Thermal protection circuitry will shut down the protection diodes. Older adjustable regulators required regulator should the junction temperature exceed 165°C protection diodes between the adjust pin and the output at the sense point. These regulators are pin compatible and between the output and input to prevent over stressing with older 3-terminal adjustable regulators, offer lower the die. The internal current paths on the LT1117 adjust dropout voltage and more precise reference tolerance. pin are limited by internal resistors. Therefore, even with Reference stability over temperature is improved over capacitors on the adjust pin, no protection diode is needed older types of regulators. to ensure device safety under short-circuit conditions. The adjust pin can be driven, on a transient basis, ± 25V with
Stability
respect to the output without any device degradation. The LT1117 family of regulators requires an output Diodes between input and output are not usually needed. capacitor as part of the device frequency compensation. The internal diode between the output and input pins of A minimum of 10μF of tantalum or 50μF of aluminum the device can withstand microsecond surge currents of electrolytic is required. The ESR of the output capacitor 10A to 20A. Normal power supply cycling can not generate should be less than 0.5Ω. Surface mount tantalum currents of this magnitude. Only with extremely large output capacitors, which have very low ESR, are available from capacitors, such as 1000μF and larger, and with the input several manufacturers. pin instantaneously shorted to ground can damage occur. When using the LT1117 adjustable device, the adjust A crowbar circuit at the input of the LT1117 in combination terminal can be bypassed to improve ripple rejection. with a large output capacitor could generate currents large When the adjust terminal is bypassed, the required value enough to cause damage. In this case a diode from output of the output capacitor increases. The device will require to input is recommended, as shown in Figure 1. an output capacitor of 22μF tantalum or 150μF aluminum D1 electrolytic when the adjust pin is bypassed. 1N4002 (OPTIONAL) Normally, capacitor values on the order of 100μF are used in the output of many regulators to ensure good LT1117 load transient response with large load current changes. V IN OUT V IN OUT Output capacitance can be increased without limit and + C ADJ R1 OUT 150μF larger values of output capacitance further improve stability and transient response. + CADJ R2 10μF 1117 F01
Figure 1
1117fd 7