LM2679SX-ADJ/NOPB

LM2679SX-ADJ/NOPB Application Field and Working Principle

The LM2679SX-ADJ/NOPB is a monolithic integrated three-terminal regulator designed to control an adjustable output voltage over a wide range of features. This LM2679SX-ADJ/NOPB device is categorized as a PMIC – Voltage Regulators – DC DC Switching Regulators.

The LM2679SX-ADJ/NOPB have the following unique advantages: First, the output current limit is adjustable, allowing the use of different loads and output requirements in different applications. A frequency compensation capacitor allows for accurate regulation and smart protection. Finally, it also has low standby current, making it suitable for long-term battery-powered applications.

Working Principle

The LM2679SX-ADJ/NOPB consists of an internal error amplifier, two series transistors, a PNP current source, and two isolated N-channel switch transistors. The error amplifier is used to compare the internal reference voltage with the feedback voltage and the voltage drop on the current limit resistor. In this circuit, the switch transistors and the power transistor (Q2) are connected in series across the output, forming a kind of closed loop.

When the voltage regulator is not in operation, a relatively small current flows through the main power transistor. When the regulator is enabled, the error amplifier supplies current to the base of the main power transistor from its collector, turning it on. The voltage and current on the transistor’s collector are now proportional to their feedback signal and are thus regulated. As soon as the output voltage reaches the desired level, the main power transistor is turned off.

The current source provides compensation for the internal error amplifier and the series transistor combination ensures that the output voltage is regulated. When the load current increases, the voltage drop on the current limit resistor increases, causing the output voltage to decrease, until the drop reaches a predetermined level. This activates the current source transistor, thus increasing the current through the sensing transistor and power transistor, resulting in a higher voltage drop, until the output voltage is again at the desired level.

Applications

The LM2679SX-ADJ/NOPB can be used in a wide range of applications, including:

• PCMCIA adapter applications
• Battery-powered portable test instruments
• Battery-powered portable communication devices
• Handheld computing devices
• Digital cameras and other imaging devices
• Portable audio players
• Battery-powered portable electronic equipment
• Data acquisition systems
• Data loggers
• Battery-powered medical instruments

Conclusion

The LM2679SX-ADJ/NOPB is a PMIC – Voltage Regulators – DC DC Switching Regulators and is a monolithic integrated three-terminal regulator designed to control an adjustable output voltage over a wide range of features. The device has adjustable output current limit, frequency compensation for accurate regulation, and relatively low standby current for long-term battery-powered applications. It is used in a variety of handheld and portable applications.