1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation

The LTC6909 is an easy to use precision oscillator that can provide 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-phase synchronized outputs. The LTC6909 also offers spread spectrum frequency modulation (SSFM), which can be enabled to improve electromagnetic compatibility (EMC) performance.

Eight separate outputs provide up to eight rail-to-rail, 50% duty cycle clock signals. Using three logic inputs, the outputs are configured for phase separation, ranging from 45° to 120° (three to eight phases). The clock outputs can also be held low or configured for Hi-Z. A single resistor, combined with the phase configuration, sets the output frequency, based on the following formula:

The LTC6909 can be used in applications requiring only one or two output phases. Alternatively, the LTC6908 family of parts provides the same two output signals but in a smaller SOT-23 or 2mm × 3mm DFN package. The LTC6908-1 provides complimentary (180°) outputs while the LTC6908-2 provides quadrature (90°) outputs.

Applications

* Synchronizing Multiple Switching Power Supplies

* 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-Phase Outputs

* 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 Floated (Hi-Z)

* Three Spread Spectrum Modulation Rates fOUT/16, fOUT/32 and fOUT/64

* 400μA Supply Current

* Operates from a Single 2.7V to 5.5V Supply

* Fast Start-Up Time

* First Cycle Accurate

* Outputs Are High Impedance Until Frequency Settles

* MS16 Package