AN718| Application Note
Maxim > App Notes > BATTERY MANAGEMENT
POWER-SUPPLY CIRCUITS
Keywords: charge pump, voltage converter, doubler, inverter, voltage splitter, DC-DC, multiplier, charge pumps
Dec 07, 2000
APPLICATION NOTE 718
Properties of the Charge-Pump Voltage Splitter
Abstract: The charge-pump voltage converter is known mostly in its doubler and inverter configuration. This article focuses on the voltage-splitter charge-pump configuration, which divides the input voltage precisely by two. Though common in many of today's DC-DC energy converters, the charge-pump voltage converter is known mostly in its doubler and inverter configurations. This article focuses on the voltage-splitter configuration, which divides a given input voltage precisely by two. After a brief review of basic charge-pump principles, two applications will be covered: the efficient generation of a regulated 3.3V from two lithium cells and the efficient derivation of a 5V supply from 10V.
The Charge-Transfer Process
Just as magnetics-based converters employ inductors, charge-pump converters use a capacitor for storing and transferring energy. For the latest charge-pump converters, recent progress in semiconductor technology has exploded the 1MHz limit for working frequency. Higher frequency allows smaller components, and the simultaneous progress in multilayer ceramic capacitor (MLCC) technology has enabled the construction of converters that are small indeed. Their low component heights allow thin converters suitable for PCMCIA cards. Charge pumps have two basic topologies, doubler and inverter, both characterized by two steps of energy transfer (Figure 1). In each case the input capacitor (Ci) ensures low impedance from the local source, which is therefore able to furnish high levels of transient current. To avoid voltage drops due to parasitic inductance, it is good practice to connect this capacitor very near the converter.
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