LTC6909_15 Datasheet, PDF (1/22 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
n _{1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-Phase Outputs}
n _{One External Resistor Sets the Output Frequency}
from 12.5kHz to 6.67MHz
n _{Optional Spread Spectrum Frequency for Improved}
EMI Performance
n _{±10% Frequency Spreading}
n _{Outputs Can Be Held Low or Floated (Hi-Z)}
n _{Three Spread Spectrum Modulation Rates}
f_OUT/16, f_OUT/32 and f_OUT/64
n _{400µA Supply Current}
n _{Operates from a Single 2.7V to 5.5V Supply}
n _{Fast Start-Up Time}
n _{First Cycle Accurate}
n _{Outputs Are High Impedance Until Frequency Settles}
n _{MS16 Package}
Applications
n _{Synchronizing Multiple Switching Power Supplies}
L, LT, LTC, LTM, Linear Technology, the Linear logo and µModule are registered trademarks
and ThinSOT is a trademark 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 im-
prove 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:
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
6909fa
1