MILPITAS, CALIF. Linear Technology says its synchronous step-down LTC1708-PG controller, designed for driving external n-channel power MOSFETs, is the first current-mode, dual-output-adjustable, two-phase type that includes a 5-bit digital-to-analog (D/A) converter.
The controller chip replaces two step-down dc/dc converters with what is said to be the industry's narrowest (0.209-inch) 36-pin SSOP, allowing for a total surface-mount solution. A 5-bit digital input sets the voltage on one output from 0.9 to 2 volts, per Intel's mobile CPU VID spec, for notebook PCs, palmtops, portable instruments and any dual-voltage compact application.
The chip's two-phase architecture (each channel 180 degrees out of phase), working nominally at 300 kHz from a 3.5- to 36-V input, cuts the number of external capacitors by up to half from a two-chip converter design, reducing total system cost, lowering EMI and improving transient response and efficiency (typically 90 percent). The company's Opti-Loop compensation optimizes transient response and minimizes the number of output capacitors. Electrical specs include output voltage accuracy within plus/minus 1 percent and worst-case load regulation of 0.5 percent. Nominal operating current is 850 microamps.
The LTC1708 draws only 20 microamps in shutdown and has dedicated shutdown pins for each output channel. A RUN/SS pin for each channel provides both soft-start and an optional, timed short-circuit shutdown. Protection features include internal foldback current limiting and an output overvoltage crowbar. A power-good output monitors both outputs. The LTC1708-PG is priced at $4.60 each in quantities of 1,000.
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EETInfo No. 641