LTC6909
1 to 8 Output, Multiphase
Silicon Oscillator with Spread
Spectrum Modulation
FEATURES
DESCRIPTION
The LTC®6909 is an easy to use precision oscillator that
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.
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1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-Phase Outputs
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One External Resistor Sets the Output Frequency
from 12.5kHz to 6.67MHz
Optional Spread Spectrum Frequency for Improved
EMI Performance
1ꢀ0 Frequency Spreadinꢁ
Outputs Can Be Held Low or Floated (Hi-Z)
Three Spread Spectrum Modulation Rates
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Eight separate outputs provide up to eight rail-to-rail,
50%dutycycleclocksignals. Usingthreelogicinputs, the
outputsareconfiguredforphaseseparation,rangingfrom
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:
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f
/16, f /32 and f /64
OUT
OUT OUT
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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
f
= 20MHz • 10k/(R
• PH)
OUT
SET
where PH = 3, 4, 5, 6, 7 or 8
APPLICATIONS
Synchronizing Multiple Switching Power Supplies
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.
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.
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TYPICAL APPLICATION
150kHz to 30MHz Output
Frequency Spectrum
(9kHz Res BW)
Providing a 4-Phase Synchronizing Clock to LTM Modules
0
–10
–20
SSFM DISABLED
10V TO 14V
INTV
CC
LTM4601
S0FT-START
0.1μF
LTC6909
–30
–40
–50
+
1.5V
48A
V D
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
OUT8
GND
TRACKING
TRACKING
TRACKING
+
LTM4601-1
V A
71.5k
SET
PH0
PH1
PH2
MOD
0.1μF
0
–10
–20
SSFM ENABLED
SSFM = f /32
OUT
LTM4601-1
LTM4601-1
–30
–40
–50
6909 TA01
ENABLE SSFM
0.01μF
DISABLE SSFM
150kHz
30MHz
FREQUENCY
(FUNDAMENTAL AND HARMONICS SHOWN)
6909 TA01b
6909f
1