LTC6909 Spread Spectrum Clock Synchronizes up to 8 Switching Regulators

Mar 10 2009 - MILPITAS, CA
  • Linear Technology announces the LTC6909, a precision silicon oscillator that significantly reduces peak radiated EMI and improves control of switching regulators in multiphase power supplies. The LTC6909 has 8 separate outputs, providing up to 8 rail-to-rail 50% duty cycle clock signals. These outputs can be used to enable or disable and phase-synchronize multiple switching regulators. Phase-synchronization offers a number of design advantages, including improved EMI performance, reduced input and output ripple current, and better load transient response. Using 3 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% of the center frequency, and the user selects one of 3 modulation rates.

    "Incorporating multiple switching regulators into a single system is much simpler with the LTC6909," says Doug LaPorte, design manager for Linear Technology. "The LTC6909 can be used to enable and disable a bank of regulators, to synchronize their operation for improved efficiency and offer vastly better EMI performance through SSFM."

    Fully specified over the temperature range of –40°C to 125°C, the LTC6909 offers rugged and reliable operation, as well as fast startup and low power consumption. These parts are available in a compact 16-lead MSOP package. 1000-piece pricing starts at $2.46 each. For more information, visit

    Summary of Features: LTC6909

    • 8 Clock Outputs Configurable in 8 Phase Settings
    • One External Resistor Sets the Output Frequency from 12.5kHz to 6.67MHz
    • Optional Spread Spectrum Frequency for Improved EMI Performance
    • ±10% Frequency Spreading
    • Outputs Can Be Held Low or Muted (Hi-Z)
    • 600µA Supply Current Typical (V+ = 5V)
    • Operates from a Single 2.7V to 5.5V Supply
    • 260µS Start-Up
    • First Cycle Accurate
    • Outputs Are High Impedance Until Frequency Settles
    • 40°C to 125°C Operating Temperature Range
    • MS16 Package

    Spread Spectrum Oscillator with 8 Phase Synchronized Outputs

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