Semtech Corp., announced the SC1158CS, a synchronous DC/DC controller with a precision 1.25V voltage reference pin. This introduction offers motherboard makers the first small, efficient, and flexible synchronous controller for the latest Instantly Available PC's. The narrow body, 16 pin SOIC package occupies only 40% the board space of other SO-20 packages.  The synchronous switcher, operating at 140kHz, provides efficiencies up to 95%. The buffered voltage reference can be flexibly configured with external circuitry to generate additional voltages, such as 3.3V for the Processor I/O, 2.5V for the clock circuitry, 1.5V for the PCI bus, and 1.8V for bus termination.

The SC1158 is a 4 bit DAC controlled synchronous switcher with 1% accuracy to power the core of the latest fast clock, high power processors, like the AMD K6-2 (2.2V), or the Cyrix MII or MGX (2.9V). Output voltages from 2.00 to 3.50V in 100mV steps are supported. The 140kHz internal oscillator is optimal for maximizing efficiency while minimizing switching losses in the FETs. The output section has a robust peak drive capability of 1.5 amps that can deliver up to 24 amps in the application circuit, depending on external component selection. The SC1158 is compliant with the "high range" of all the latest Intel VRM specifications. For Instantly Available PC applications, the voltage reference supports S3 and higher sleep states when connected to the 5 volt standby circuit of the power supply.

With a great deal of acceptance of Semtech controller parts in the computer industry already, this 1.25-V reference is both timely and well focused. It will receive numerous design wins and is well-situated for the majority of today's operations and those for the next 12 - 18 months for the 2 to 3-V families that are out there. The efficiency is high and the package size is small. Note that there is no attempt to increase efficiencies at low loads with different modulation technology; although savings in power could be made they would be trivial compared to maximizing efficiency at or near full load.

From a user point of view I prefer the lower frequencies of operation from 100 to 150 kHz; I find that 200 kHz parts in computers or in the ac adaptors for laptops causes much more intereference to AM radio (I live in the sticks.)