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A simple model for DC/DC charge pumps

Posted: 22 Jul 2008     Print Version  Bookmark and Share

Keywords:DC/DC charge pumps  flying capacitors  LDO regulators  inductive switching regulators 

This application note from AnalogicTech summarises the benefits and limitations of charge pump DC/DC converters for low-current portable applications, typically below 300mA output current.

Charge pumps provide higher operating efficiency and increased input and output noise when compared to LDO regulators. They are a cost-effective solution and do not require a magnetic component, as required with inductive switching regulators.

Multi-mode step-down and step-up DC/DC charge pumps utilising two flying capacitors were presented. An equivalent DC model was provided which predicts charge pump efficiency and maximum output current. The model includes a voltage-dependent voltage source, a series modulation resistance (RM) and output resistance (ROUT). The mode variable M is selected by the charge pump IC to maintain maximum efficiency, while output regulation is achieved by modulating the switching duty cycle and/or frequency. The operating mode determines the flying capacitor arrangement, sets charge pump fractional input-to-output gain, and impacts the input voltage headroom.

View the PDF document for more information.

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