LTC6909 Datasheet, PDF (1/20 Pages) Linear Technology – 1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation

LTC6909
1 to 8 Output, Multiphase
Silicon Oscillator with Spread
Spectrum Modulation
FEATURES
■ _{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}
f_OUT/16, f_OUT/32 and f_OUT/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}
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.
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.
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:
f_OUT = 20MHz • 10k/(R_SET • PH)
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.
TYPICAL APPLICATION
Providing a 4-Phase Synchronizing Clock to LTM Modules
10V TO 14V
0.1μF
0.1μF
71.5k
LTC6909
V⁺D
OUT1
GND OUT2
V⁺A
OUT3
SET
OUT4
PH0 OUT5
PH1 OUT6
PH2 OUT7
MOD OUT8
ENABLE SSFM
0.01μF
DISABLE SSFM
INTV_CC
LTM4601
S0FT-START
TRACKING
LTM4601-1
TRACKING
LTM4601-1
TRACKING
LTM4601-1
1.5V
48A
6909 TA01
150kHz to 30MHz Output
Frequency Spectrum
(9kHz Res BW)
0
SSFM DISABLED
–10
–20
–30
–40
–50
0
SSFM ENABLED
–10
SSFM = f_OUT/32
–20
–30
–40
–50
150kHz
FREQUENCY
30MHz
(FUNDAMENTAL AND HARMONICS SHOWN)
6909 TA01b
6909f
1