LT1579

Features:

Daisy-Chained Control Outputs
Maintains Output Regulation with Dual Inputs
Dropout Voltage: 0.4V
Output Current: 300mA
50mA Quiescent Current
No Protection Diodes Needed
Two Low-Battery Comparators
Status Flags Aid Power Management
Adjustable Output from 1.5V to 20V
Fixed Output Voltages: 3V, 3.3V and 5V
7mA Quiescent Current in Shutdown
Reverse-Battery Protection
Reverse Current Protection
Remove, Recharge and Replace Batteries Without Loss of Regulation


Application

Dual Battery Systems
Battery Backup Systems
Automatic Power Management for Battery-Operated Systems


Specifications

Power Input Pin Voltage ...................................... ±20V*
Output Pin Voltage
Fixed Devices............................................. 6.5V, 6V
Adjustable Device ............................................ ±20V*
Output Pin Reverse Current .................................... 5mA
ADJ Pin Voltage .............................................. 2V, 0.6V
ADJ Pin Current ...................................................... 5mA
Control Input Pin Voltage ............................ 6.5V, 0.6V
Control Input Pin Current ....................................... 5mA
BIASCOMP Pin Voltage ............................... 6.5V, 0.6V
BIASCOMP Pin Current .......................................... 5mA
Logic Flag Output Voltage ............................ 6.5V, 0.6V
Logic Flag Input Current ......................................... 5mA
Output Short-Circuit Duration .......................... Indefinite
Storage Temperature Range ................. 65 to 150
Operating Junction Temperature Range .... 0 to 125
Lead Temperature (Soldering, 10 sec).................. 300


Description

The LT®1579 is a dual input, single output, low dropout regulator. This device is designed to provide an uninterruptible output voltage from two independent input voltage sources on a priority basis. All of the circuitry needed to switch smoothly and automatically between inputs is incorporated.

The LT1579 can supply 300mA of output current from either input at a dropout voltage of 0.4V. Quiescent current is 50mA, dropping to 7mA in shutdown. Two comparators are included to monitor input voltage status. Two additional status flags indicate which input is supplying power and provide an early warning against loss of output regulation when both inputs are low. A secondary select pin is provided so that the user can force the device to switch from the primary input to the secondary input. Internal protection circuitry includes reverse-battery protection, current limiting, thermal limiting and reversecurrent protection.

The device is available in fixed output voltages of 3V, 3.3V and 5V, and as an adjustable device with a 1.5V reference voltage. The LT1579 regulators are available in narrow 16-lead SO and 16-lead SSOP packages with all features, and in SO-8 with limited features.