MIC4685WR

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The MIC4685WR is a wide input range buck converter designed for 5V or 3.3V output applications. It provides an adjustable output voltage, adjustable current limit, and adjustable output frequency. The converter utilizes synchronous rectification, allowing for efficiency as high as 95% and providing lower output voltage ripple. Features include programmable Soft Start and Forced Pulse-By-Pulse Current Limit.

The MIC4685WR is part of the family of integrated switch-mode dc-dc controllers. It is designed to regulate step-down (buck) dc-dc converter with an input voltage range of 4.5 to 45V and output voltage as low as 0.7V with a wide selection of output current levels. The MIC4685WR is available in a space-saving, thermally enhanced SOT-23-6 package.

Applications

• Frequency Modulated Converters
• Notebook Computers
• Battery Powered Systems
• Telecommunications

Working Principle

The MIC4685WR is a high-performance chip tailored to potentio-metric applications. The converter incorporates a voltage feedback loop which can drive an N-channel MOSFET synchronous rectifier switch with a programmable frequency and modulation characteristics. The chip synchronizes with the rising edge of the output voltage waveform, ensuring the loss of the internal circuit references as well as preserving the operating parameters at every switching cycle.

The chip is designed to operate in discontinuous mode (DCM) and in continuous conduction mode (CCM) with a current set by an external resistor. In DCM, the output inductor current ramps up and drops to zero, wile in CCM, the current will always remain above a minimum limit and the output voltage is determined by the master oscillator\'s duty cycle.

When controlling the switch mode, the chip monitors current peak, current valley, input voltage and output voltage; it adjusts the duty cycle as needed to regulate the output voltage, driving the synchronous rectifier following the output waveform. The current limit protection allows the MIC4685WR to limit the output current to a predefined level, preventing device failure.

To provide additional reliability, is possible to adjust the number of cycles used to overdrive the output voltage during LED startup and recovery, adjusting the turn-on and turn-off times of the synchronous rectifier.

The MIC4685WR provides an efficient method of controlling isolated dc-dc converters. It is tailored to a wide variety of applications, offering small solution size, high efficiency and adjustable current limit.

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