MILPITAS, Calif. The LTC1735 and LTC1736 from Linear Technology Corp. are designed as high-efficiency step-down dc/dc controllers for powering the newest Intel Pentium II processors in notebook computers.
The devices' fixed-frequency current-mode architecture and Opti-Loop compensation provide accurate dc output and fast transient response with minimal external components, according to LTC. They also include a proprietary soft latch scheme that protects against harmful overvoltage and overcurrent faults without requiring the system to reset after the fault has disappeared.
The LTC1736 uses an integrated 5-bit D/A converter to set the output voltage from 0.925 V to 2.00 V, in accordance with Intel's Mobile Pentium II specifications. The LTC1735 uses two external resistors to set the output from 0.8 V to 6 V to address a range of output-voltage requirements. An internal plus/minus1 percent accurate 0.8-V reference assures compatibility with future generations of microprocessors requiring core voltages below 1 V.
The LTC1735 and LTC1736 both operate from 3.5 V to 36 V to accommodate a variety of input supply options. Their nominal 300-kHz operating frequency minimizes the size of external components to provide the smallest total solution. Other features include remote output voltage sensing, programmable soft start and internal current foldback.
The LTC1735 and LTC1736 are synchronous step-down switching-regulator controllers that drive external n-channel power MOSFETs using a fixed-frequency Opti-Loop architecture with Burst Mode for optimized efficiency at all load conditions. Opti-Loop compensation effectively removes the output capacitor constraints placed on many other controllers to insure stable operation. A maximum duty-cycle limit of 99 percent provides low-dropout operation, which extends operating time in battery-powered systems.
A forced continuous-control pin reduces noise and RF interference and can assist secondary winding regulation by disabling burst mode when the main output is lightly loaded. Soft start is provided by an external capacitor that can be used for sequencing in multiple supply applications.
The LTC1735 is available from stock in 16-lead SSOP and SO packages with prices starting at $3.20 in 1,000-piece quantities. The LTC1736 is available in a 24-lead SSOP with prices starting at $3.50 in 1,000-piece quantities.
Call (408) 432-1900
Issue of January 4, 1999; EETInfo No. 605