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Electronic Design

Two-Phase Controller Maximizes Efficiency And Minimizes Ripple

A current-mode synchronous step-down switching regulator known as the LTC3716 efficiently converts power for mobile-computer CPUs. It uses two-phase techniques to maximize efficiency and minimize input and output ripple currents.

This two-phase controller drives its two output stages out of phase at frequencies up to 300 kHz, reducing RMS ripple currents in both the input and output capacitor and cutting noise induced by the power supply. By effectively doubling the fundamental frequency to lower the value of the output capacitors, the two-phase technique operates each channel at an optimum frequency for efficiency.

In this scheme, the switching regulator controller drives two n-channel external MOSFETs 180° out of phase in a fixed-frequency operation. To provide an output in the 0.6- to 1.75-V range within 1% accuracy, the switching regulator implements the 5-bit mobile VID code. This current-mode regulator ensures load current sharing, so it accepts a dual input supply. Also, the unit offers a wide input range of 4 to 36 V.

The LTC3716 provides three modes of operation. While the PWM mode forces continuous current operation with the least efficiency at full load, the burst mode is intended for low currents and maximum efficiency. Though not as efficient as the burst mode, the cycle-by-cycle or cycle-skip mode provides lower noise over a wide output current operation.

An internal differential amplifier enables true remote sensing of the regulated supply's positive and negative output terminals. An optiloop compensation technique permits lower output capacitor and ESR values. Other features include adjustable soft-start current ramping, internal current fold-back, and short-circuit shutdown.

The LTC3716 comes in a 36-pin narrow SSOP package. It is priced at $4.45 each in quantities of 1000 units.

Linear Technology Corp., 1630 McCarthy Blvd., Milpitas, CA 95035-7417; (408) 432-1900;

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