LM2677SX-5.0

The LM2677SX-5.0 is part of a range of switch mode power supply controllers, manufactured by National Semiconductor and marketed as a “Simple Switcher”. The device is specifically designed for high current, low voltage power supply applications, offering efficiency and reduced PC board area.

It is a non-isolated step-down regulator with a wide input voltage range from 4.8V to 40V and an adjustable output voltage from 0.8V to 20V. The LM2677SX-5.0 can handle up to 5A of output current with up to 97% peak efficiency, while maintaining low ripple and fast transient response. Built-in loop compensation allows an easy single resistor voltage setting and a 5V fixed output of 250mA is available independently of the VOUT pin setting.

The LM2677SX-5.0 is suitable for applications where high current and low heat dissipation are required, such as notebook computers, telecommunication systems, imaging systems and distributed power architectures. It is also suitable for powering low voltage memory, disk drives, electric motors and LED lighting.

Application Field

The LM2677SX-5.0 is commonly used in a wide range of applications, including:

• Low power computing, including computer motherboards, servers and laptops
• AV-appliances such as TV sets, set-top boxes, DVD players and PDAs
• High speed communication equipment such as VDSL modems, DSL Routers and DSLAMs
• Mobile devices such as PDAs and cell phones
• Distributed power architectures such as telecom base stations

Working Principle

The LM2677SX-5.0 is a non-isolated step-down regulator, which typically consists of an input voltage converter, high current output stage, control and feedback circuitry. The input voltage converter is responsible for converting the high voltage input into a low voltage, which is then used to drive the high current output stage. The control and feedback circuitry monitor output voltage and current and provide the necessary compensation and control inputs to maintain the stability of the transformer circuit.

The LM2677SX-5.0 features various safety features such as over-voltage protection, over-current protection, output short-circuit protection and thermal shutdown. In addition, the device incorporates a frequency jittering function that reduces EMI emissions.