LTC6908-1/LTC6908-2
1
690812fa
690812 TA01b
FREQUENCY
(FUNDAMENTAL AND HARMONICS SHOWN)
150kHz
0
–10
–20
–30
–40
0
–10
–20
–30
–40
OUTPUT
(dBc)
OUTPUT
(dBc)
30MHz
SSFM DISABLED
SSFM ENABLED
Resistor Set SOT-23
Oscillator with Spread
Spectrum Modulation
The LTC6908 is an easy-to-use precision oscillator that
provides 2-outputs, shifted by either 180° or 90°. The
oscillator frequency is programmed by a single external
resistor (RSET)andspreadspectrumfrequencymodulation
(SSFM) can be activated for improved electromagnetic
compatibility (EMC) performance.
The LTC6908 operates with a single 2.7V to 5.5V supply
and provides rail-to-rail, 50% duty cycle square wave
outputs. A single resistor from 10k to 2M is used to select
an oscillator frequency from 50kHz to 10MHz (5V supply).
The oscillator can be easily programmed using the simple
formula outlined below:
fOUT =10MHz 10k/RSET
The LTC6908’s SSFM capability modulates the output
frequency by a pseudorandom noise (PRN) signal to
decrease the peak electromagnetic radiation level and
improve EMC performance. The amount of frequency
spreading is xed at ±10% of the center frequency. When
SSFM is enabled, the rate of modulation is selected by the
user. The three possible modulation rates are fOUT/16,
fOUT/32 and fOUT/64.
■ Switching Power Supply Clock Reference
■ Portable and Battery-Powered Equipment
■ Precision Programmable Oscillator
■ Charge Pump Driver
■ LTC6908-1: Complementary Outputs (0°/180°)
■ LTC6908-2: Quadrature Outputs (0°/90°)
■ 50kHz to 10MHz Frequency Range
■ One External Resistor Sets the Frequency
■ Optional Spread Spectrum Frequency Modulation
for Improved EMC Performance
■ ±10% Frequency Spreading
■ 400A Supply Current Typical (V+ = 5V, 50kHz)
■ Frequency Error ≤1.5% Max (TA = 25°C, V+ = 3V)
■ ±40ppm/°C Temperature Stability
■ Fast Start-Up Time: 260s Typical (1MHz)
■ Outputs Muted Until Stable
■ Operates from a Single 2.7V to 5.5V Supply
■ Available in Low Prole (1mm) ThinSOT and DFN
(2mm
× 3mm) Packages
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2.25MHz, 2.5V/8A Step-Down Regulator
TYPICAL APPLICATIO
U
CBYP
44.2k
OUT1
OUT2
fOUT = 10MHz 10k/RSET
MOD
V+
GND
SET
690812 TA01a
SVIN TRACK
LTC3418
RT
CIN
100
F
0.2
H
LTC6908-1
RUN/SS
ITH
PGOOD
SW
PGND
SGND
SYNC/MODE VFB
PVIN
820pF
1000pF
0.1
F
COUT
100
F
×2
VOUT
2.5V
8A
4.32k
2k
41.2k
2.2M
VIN
2.8V TO 5.5V
4.99k
150kHz to 30MHz Output
Frequency Spectrum
(9kHz Res BW)