Dual Monolithic 300mA Synchronous Step-Down Regulator

The LTC3547B is a dual, 2.25MHz, constant-frequency, synchronous step-down DC/DC converter in a tiny 3mm × 2mm DFN package. 100% duty cycle provides low dropout operation, extending battery life in portable systems. Low output voltages are supported with the 0.6V feedback reference voltage. Each regulator can supply 300mA continuous output current.

The input voltage range is 2.5V to 5.5V, making it ideal for Li-Ion polymer and USB powered applications. Supply current is only 1µA in shutdown.

An internally set 2.25MHz switching frequency allows the use of tiny surface mount inductors and capacitors. Internal soft-start reduces inrush current during start-up. All outputs are internally compensated to work with ceramic capacitors. The LTC3547B is available in a low profile (0.75mm) 3mm × 2mm DFN package. The LTC3547B is also available in a fixed output voltage configuration selected via internal resistor dividers.

Applications

* Cellular Telephones

* Digital Still Cameras

* Wireless and DSL Modems

* Portable Media Players

* PDAs/Palmtop PCs

* High Efficiency (Up to 96%) Dual Step-Down Outputs

* 300mA Output Current per Channel at VIN = 3V

* 2.25MHz Constant-Frequency Operation

* 2.5V to 5.5V Input Voltage Range

* Low Dropout Operation: 100% Duty Cycle

* No Schottky Diodes Required

* Internally Compensated for All Ceramic Capacitors

* Independent Internal Soft-Start for Each Channel

* Available in Fixed Output Versions

* Current Mode Operation for Excellent Line and Load Transient Response

* 0.6V Reference Allows Low Output Voltages

* Short-Circuit Protected

* Ultralow Shutdown Current: IQ < 1µA

* Low Profile (0.75mm) 8-Lead 3mm × 2mm DFN Package