Adaptive-Frequency Current Mode Switching Regulators

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The LT1500 is an adaptive-frequency current mode step-up switching regulator with an internal power switch that is rated up to 700mA. In contrast to pulse skipping switching regulators, the LT1500 uses a current mode topology that provides lower noise operation and improved efficiency. Only at very light loads is Burst Mode™ activated to give high efficiency and micropower operation. High switching frequency (up to 500kHz) allows very small inductors to be used, along with ceramic capacitors if desired.

The LT1500 operates with input voltages from 1.8V to 15V and has only 200µA operating current dropping to 8µA in shutdown. A low-battery comparator is included which stays alive in shutdown. A second output feedback pin with negative polarity allows negative output voltages to be regulated when the switcher is connected up as a Cuk or a flyback converter.

Two package types are available. The LT1500 comes in a 14-pin SO package, with two options available for fixed output (3.3V or 5V) or adjustable operation. A reduced feature part, the LT1501, comes in the smaller 8-pin SO package with internal frequency compensation. It is also available in adjustable and fixed output voltage versions.

Applications

* Portable Instrumentation

* Battery Operated Systems

* PDA's

* Standby Power

* Low Noise Adaptive-Frequency Current Mode Operation Avoids Low Frequency Noise at Most Load Currents

* Can Be Externally Synchronized (LT1500)

* Micropower Quiescent Current: 200µA

* Shutdown Current: 8µA Typ

* Internal Loop Compensation