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Low dropout voltage regulators

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TWO new 300mA low-noise, low dropout (LDO) regulators, each packaged in a 3mm x 3mm PowerPAK MLP33, have been released by Siliconix, represented by Braemac .

Designed for use in battery-powered equipment such as cell phones, wireless handsets and modems, PDAs, notebooks, pagers and digital cameras, the new ICs are small enough to fit on tiny circuit boards in miniaturised wireless devices while handling up to 1.2W of power dissipation.

The Si91871 and Si91872 feature a low ground current - ideal for low-voltage battery-operated power systems - and low dropout voltage of 250mV at 300mA, prolonging battery life in portable electronics.

Designed to maintain regulation while delivering 400mA peak output current in applications with high surge currents at turn-on, the Si91871 and Si91872 are available in a range of 14 fixed output voltage options from 1.2V to 5.0V.

Both devices feature 1.5% guaranteed output voltage accuracy, a fast start-up time of 60µs, and fast transient response of <30µs.

A built-in active pull-down clamp circuit improves transient response and regulation by actively sinking current from the output if it exceeds the desired regulation voltage.

Both devices discharge the output during shutdown mode through a 100Ω n-channel MOSFET. Integrated short-circuit and thermal protection ensure reliable operation.

Reverse battery protection limits reverse current flow to a 1µA maximum shutdown current. When no output is required, an ON/OFF feature allows digital circuitry to shut off the device to save power.

Designers will choose between the Si917871 and Si91872 depending on the specifics of their application. The Si91871 is especially suited for sensitive RF receiver or audio amplifier environments, with an external noise bypass capacitors that reduces output noise to just 30µV(rms), while the Si91872 provides an out-of-regulation error flag.

The Si91871 and Si91872 may be used with low-ESR ceramic capacitors or tantalum capacitors, giving designers a flexible choice of magnetic components.

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