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Spread spectrum clock has eight separate outputs

Posted: 16 Mar 2009     Print Version  Bookmark and Share

Keywords:precision silicon oscillator  multi-phase power supplies  clock frequency  Phase-synchronisation 


Linear Technology has introduced LTC6909, a precision silicon oscillator that significantly reduces peak radiated EMI and improves control of switching regulators in multi-phase power supplies.

The LTC6909 has eight separate outputs, providing up to eight rail-to-rail 50 per cent duty cycle clock signals. These outputs can be used to enable or disable and phase-synchronise multiple switching regulators. Phase-synchronisation offers a number of design advantages, including improved EMI performance, reduced input and output ripple current, and better load transient response. Using three logic inputs, the phase relationship between these outputs can be configured from 45° to 120°, or the outputs can be placed in a logic low or high-Z state.

A single resistor selects the output frequency from 12.5kHz to 6.67MHz. The LTC6909 also offers spread spectrum frequency modulation (SSFM), a technique that modulates the clock frequency by a pseudorandom signal. SSFM is easily enabled and offers a method for decreasing peak electromagnetic emissions. The amount of frequency spreading is fixed at ±10 per cent of the centre frequency, and the user selects one of three modulation rates.

Fully specified over the temperature range of -40°C to 125°C, the LTC6909 offers rugged and reliable operation, as well as fast start-up and low power consumption. These parts are available in a compact 16-lead MSOP package.

The LTC6909 is now available. In 1K quantities, pricing starts at Rs.122.31s ($2.46) each.

- Ismini Scouras

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