Charge Pumps

Charge pumps are circuits that generate higher voltages from low-voltage inputs by using capacitors as storage elements. Charge pumps are used in notebook computers and mobile phones. There are many types of charge pumps. Examples include charge pump phase-locked loops (CPPL), converter chips, IC converters, inductorless converters, and inductorless regulators. A charge pump phase-locked loop (CPPLL) can provide zero phase-error and an extended frequency range of operations. Converter chips can be used for both analog/digital (A/D) and digital/analog (D/A) conversions. IC converters are used in battery-operated, handheld devices. An inductorless converter can be used as a DC-DC inverter, splitter, or doubler. An inductorless regulator provides output regulation for portable applications. Specialized and proprietary charge pumps may also be available.

Selecting charge pumps requires an understanding of charge pump (CP) technologies and an analysis of product specifications. Depending on the controller and circuit typology, a charge pump (CP) can double voltages, invert voltages, or generate arbitrary voltages. In some products, a charge pump circuit can provide efficiencies as high as 90 to 95%. A charge pump PLL (CPPLL) circuit can be sized to satisfy performance requirements. Important specifications for a charge pump phase-locked loop (CPPLL) include output frequency range, phase margin, reference frequency to unity-gain-bandwidth-ratio (RUR), and locking time. Regulated output voltage, input voltage, output current, quiescent current, switching frequency, efficiency, and operating temperature should be considered when selecting DC/DC converter chips. Specifications for A/D converter chips include resolution, sample rate, input voltage range, and operating temperature. Properties such as input voltage range, output specifications, efficiency, and operating temperature should be considered before using IC converters. An inductorless regulator requires a minimum supply voltage and a multi-cell alkaline battery or a single-cell lithium-ion (Li-ion) battery. Other charge pumps may carry additional specifications.

Charge pumps are used in RS232 level shifters and EPROM circuits. A charge pump PLL (CPPLL) can also be used in frequency synthesis. Converter chips are used in data-acquisition, communications, instrumentation, signal processing, and power management applications. An inductorless converter can be used to optimize battery life in portable devices. An inductorless regulator can be used to provide constant-current backlight in white light emitting diode (LED) applications. Charge pumps are also used in white LED backlight, liquid crystal display (LCD), and Flash applications.

• Applying the TC1219/TC1220 Inverting Charge Pumps with Small External Capacitor Values
  Microchip Technology Inc.'s TC1219 (switching frequency at 12 kHz) and TC1220 (switching frequency at 35 kHz) are inverting charge pump voltage converters that are specified using rather large...
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• Design Guideline: AAT3190 Positive/Negative Charge Pump
  This Application Note presents the design guideline and load line characteristics for the AAT3190 positive/negative charge pump with voltage multiplier stage. With a few external passive components,...
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• The Evolution of Switched Capacitor Backlight Drivers in Mobile Phones
  Today the majority of mobile phones use white LEDs to provide backlighting for the color display. Nearly every phone designer strives to drive the backlight with the most efficient, smallest size, and...
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Part Numbers for Charge Pumps