DC-DC Converter Chips

DC-DC converter chips provide a regulated DC voltage output from a different, unregulated input voltage. They are used in power management applications and incorporate several conversion technologies. Buck or step-down converters convert a higher DC input voltage to a lower DC output voltage of the same polarity. Using a transistor as a switch, buck converters alternately connect and disconnect the input voltage to an inductor. Boost or step-up converters convert a lower DC input voltage to a higher DC output voltage of the same polarity. Buck-boost converters can be used for either step-up or step-down conversions, and to reverse or invert voltage polarity. CUK converters use capacitive energy transfers, creating a smooth current at both sides of the converter. Charge pump converters are suitable for voltage step-up or voltage inversion in low power applications. Unlike most other DC-DC converter chips, charge pumps store energy in a capacitor instead of an inductor. Flyback converters are similar to buck-boost converters, but use a transformer to store energy and provide isolation between the input and output. These devices have two distinct phases for energy storage and delivery. Forward converters are similar to flyback converters, but use transformers in a more traditional manner, transferring energy from input to output in a single step.

Important specifications for DC-DC converter chips include regulated output voltage, input voltage, output current, quiescent current, switching frequency, efficiency, and operating temperature. Both the output regulated voltage (V_olt) and the input voltage (V_IN) are minimum and maximum amounts in continuous mode (DC). The output current (I_OUT) is measured under specified conditions. Measured in amperes (A) during the idling state, the quiescent current never makes it to the load. Instead, it flows from the battery to power the regulator itself. Efficiency, the ratio of output power to input power, measures the ability of DC-DC converter chips to convert input energy into output energy. For example, an efficiency of 100% means that all of the input energy is transferred to the output. 

DC-DC converter chips are available with a variety of features. Some devices have more than one output or channel. Others have an internal circuit to control the amount of current produced, or an error flag for monitoring outputs that drop below a nominal value. Reverse voltage protection prevents damage in applications where users can accidentally reverse battery polarity. Thermal shutdown protection turns off DC-DC converter chips when the temperature exceeds a predefined limit. Shutdown (inhibit) pins are used to disable regulator outputs. For switching applications, converters sometimes use metal-oxide silicone field-effect transistors (MOSFET) instead of diodes. Synchronous rectification means that the MOSFETs are turned on and off at the right time for efficient gating or rectification of the output.

DC-DC converter chips are available in a variety of IC package types. Dual in-line packages (DIP) can be made of ceramic (CIP) or plastic (PDIP). Quad flat packages (QFPs) contain a large number of fine, flexible, gull wing shaped leads. SC-70, one of the smallest available IC packages, is well-suited for applications where space is extremely limited. Small outline (SO) packages are available with 8, 14, or 20 pins. Transistor outline (TO) packages are commonly available. TO-92 is a single in-line package used for low power devices. TO-220 is suitable for high power, medium-current, and fast-switching products. TO-263 is the surface-mount version of the TO-220 package. Other IC packages for DC-DC converter chips include shrink small outline package (SSOP), small outline integrated circuit (SOIC), small outline package (SOP) and small outline J-lead (SOJ).

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Part Numbers for DCDC Converter Chips