300mA Dual Input Smart Battery Backup Regulator

The LT1579 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 50µA, dropping to 7µA 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 reverse-current 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.

Applications

* Dual Battery Systems

* Battery Backup Systems

* Automatic Power Management for Battery-Operated Systems

* Maintains Output Regulation with Dual Inputs

* Dropout Voltage: 0.4V

* Output Current: 300mA

* 50µA 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

* 7µA Quiescent Current in Shutdown

* Reverse-Battery Protection

* Reverse Current Protection

* Remove, Recharge and Replace Batteries Without Loss of Regulation