Vishay Siliconix is adding to its family of power products for telecom applications with two new programmable duty cycle controller ICs and a 200-V power MOSFET which together provide a compact, affordable converter solution for NT1, NT1+, ISDN, and PBX distributed power applications, as well as dc-to-dc converter modules.

The new Si9118DY and Si9119DY PWM controller ICs allow forward and flyback converters to be implemented at frequencies up to 1 MHz. Allowing input voltages ranging from 10 V to 200 V, the Si9118DY and Si9119DY operate at constant frequency mode during full load conditions, and automatically switch to pulse-skipping mode under light loads to maintain high efficiency throughout the full load range.

Both devices feature programmable duty cycle control, allowing up to 80% duty cycles at a 1-MHz switching frequency. Thus in applications where wide input voltage and load conditions need duty cycles above 50%, the converters can be configured to provide optimal efficiency, while reducing the complexity of the transformer design. It likewise makes the Si9118DY and Si9119DY suitable for applications ranging in power levels from 2 W to 50 W, allowing manufacturers to use the same power IC for a number of different end products.

"Telecom designers put a premium on solutions that are efficient, elegant, and easy to implement," said Tony Armstrong, Senior Product Marketing Manager at Vishay Siliconix. "The Si9118DY and Si9119DY, together with the Si9422DY LITTLE FOOT power MOSFET, combine all of these benefits in addition to improved system reliability and a very affordable total solution cost."

Both the Si9118DY and Si9119DY are packaged in the surface-mount SOIC-16 and provide a programmable soft-start feature that allows inrush current control with the addition of an external capacitor. Other features include a 4-V voltage reference, 2.7-MHz bandwidth error amplifiers, standby mode, and under-voltage lockout circuitry.

For applications requiring synchronization of several controllers, the Si9119DY offers a clock synchronization pin which allows an external signal to control the high-to-low transition. When the SYNC pins are connected together, the converters will lock to the highest switching frequency, the fastest controller becoming the master.

As an alternative option, the Si9118DY allows designers to simplify the slope compensation circuitry with a buffered oscillator ramp signal that can be used for external slope compensation. In duty cycles greater than 50%, slope compensation stabilizes the inner current loop and maintains overall loop stability.

Completing the active components needed for a total solution, the new Si9422DY LITTLE FOOT power MOSFET combines a 200-V breakdown voltage with the lowest on-resistance ever offered for this device type in an SO-8 package, just 420 milliohms . In many cases, the Si9422DY will allow designers to replace a DPAK or TO-220, simplifying PC board layout and streamlining the assembly process.

In addition to offering low on-resistance, the Si9422DY has been optimized for PWM applications with a typical gate charge of just 13 nC, less than half the level of competing devices. This low Q_g ensures that power conversion efficiency is maximized at all load levels.

These two controllers offer the kind of higher frequency limit that is being looked for by OEMs and a voltage range that will solve a lot of problems; as Siliconix suggests, the products will end up in a range of power supplies with a wide range of power levels. The pulse-skipping mode is the simplest technology I have yet seen to ensure a controllers retain efficiency at lower loads. Because the process is automatic it will simplify other design elements as well. The soft-start and standby modes are, of course, necessities for today's market.

The clock synchronization pin on the Si9119DY is another beautiful simplifier for the circuit designer provided the controllers involved are working at the about the same loads -- because of the use of the highest frequency as master -- while the alternate option of the external slope corrector in the Si9118DY will allow the design of some extremely stable, special-purpose supplies. All the devices, including the Si9422DY power MOSFET, are in production.