LTC6909

1

6909f

1 to 8 Output, Multiphase

Silicon Oscillator with Spread

Spectrum Modulation

can provide 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-phase synchro-

nized outputs. The LTC6909 also offers spread spectrum

frequency modulation (SSFM), which can be enabled to

improve electromagnetic compatibility (EMC) perfor-

mance.

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:

where PH = 3, 4, 5, 6, 7 or 8

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.

■

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

■

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

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Providing a 4-Phase Synchronizing Clock to LTM Modules

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Protected by U.S. Patents, including

6342817, 6614313, 7417509.

LTC6909

10V TO 14V

0.1μF

71.5k

0.1μF

0.01μF

ENABLE SSFM

DISABLE SSFM

LTM4601

LTM4601-1

LTM4601-1

LTM4601-1

TRACKING

S0FT-START

1.5V

48A

TRACKING

TRACKING

6909 TA01

GND

SET

PH0

PH1

PH2

MOD

OUT1

OUT2

OUT3

OUT4

OUT5

OUT6

OUT7

OUT8

FREQUENCY

(FUNDAMENTAL AND HARMONICS SHOWN)

150kHz

–20

–10

0

6909 TA01b

–30

–40

–50

30MHz

–20

–10

0

–30

–40

–50

SSFM DISABLED

SSFM ENABLED

150kHz to 30MHz Output

Frequency Spectrum

(9kHz Res BW)