Electronic Design

Low-V<sub>IN</sub> Buck Regulator Toggles Fast-Switching/Very Low-Dropout Modes

The LTC3448 goes after applications in devices powered by single-cell lithium-ion, multicell alkaline, or nickel-metal-hydride batteries. Developed by Linear Technology, this 600-mA (continuous) buck regulator transitions from switch mode (at a constant 1.5 or 2.25 MHz) to a 160-mV very low-dropout (VLDO) mode when load current drops below 3 mA.

Quiescent current is only 32 μA in VLDO mode. Once the output current again rises beyond 11 mA, the switching mode toggles back on.

At moderate output load levels, pulseskipping provides very low output voltage ripple. (Actual values depend on switching frequency and component selection.) In LDO mode, output voltage ripple is less than 5 mV p-p.

Input voltage can be as low as 1.4 V for fixed output voltages down to 1.2 V. Fixed 1.5- and 1.8-V options also are available. Low input voltage is important for emerging applications that employ a 1.5-V main rail bucked down to 1.2 V for low-voltage microprocessor and microcontroller cores.

Most power-supply designers would choose to run the chip at 1.5 MHz. But for automotive applications, switching at 2.25 MHz puts the fundamental frequency above the frequency of the car radio's AM-band local oscillator.

Either frequency permits the use of the latest small surface-mount inductors and low-ESR (equivalent series resistance) capacitors. The combination of tiny externals and a 3- by 3-mm DFN-8 (or MSOP-8E) provides a compact footprint for handheld applications.

Alternatively, the LTC3448 can be externally synchronized to operate anywhere between 1.5 and 4 MHz via its sync pin. Synchronization to an external source is useful in noise-sensitive or RF applications, where it can keep the switching rate out of noise-sensitive bands.

Pricing starts at $2.05 each in 1000-piece quantities.

Linear Technology

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