LTC6908-2_15 Datasheet, PDF (1/16 Pages) Linear Technology – Resistor Set SOT-23 Oscillator with Spread Spectrum Modulation

FEATURES
■ _{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}
■ _{400µA Supply Current Typical (V}⁺ _{= 5V, 50kHz)}
■ _{Frequency Error ≤1.5% Max (TA = 25°C, V}⁺ _{= 3V)}
■ _{±40ppm/°C Temperature Stability}
■ _{Fast Start-Up Time: 260µs Typical (1MHz)}
■ _{Outputs Muted Until Stable}
■ _{Operates from a Single 2.7V to 5.5V Supply}
■ _{Available in Low Profile (1mm) ThinSOT and DFN}
(2mm × 3mm) Packages
U
APPLICATIO S
■ _{Switching Power Supply Clock Reference}
■ _{Portable and Battery-Powered Equipment}
■ _{Precision Programmable Oscillator}
■ _{Charge Pump Driver}
LTC6908-1/LTC6908-2
Resistor Set SOT-23
Oscillator with Spread
Spectrum Modulation
DESCRIPTIO
The LTC^®6908 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 (R_SET) and spread spectrum frequency modulation
(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:
f_OUT =10MHz • 10k/R_SET
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 fixed 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 f_OUT/16,
f_OUT/32 and f_OUT/64.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
2.25MHz, 2.5V/8A Step-Down Regulator
V_IN
2.8V TO 5.5V
C_BYP
0.1µF
V⁺
OUT1
LTC6908-1
GND OUT2
44.2k
SET MOD
690812 TA01a
f_OUT = 10MHz • 10k/R_SET
2.2M
1000pF
41.2k
4.99k
SV_IN TRACK PV_IN
R_T
SW
LTC3418
PGOOD
RUN/SS PGND
I_TH
SGND
SYNC/MODE V_FB
820pF
4.32k
C_IN
100µF
0.2µH
2k
V_OUT
2.5V
8A
C_OUT
100µF
×2
150kHz to 30MHz Output
Frequency Spectrum
(9kHz Res BW)
0
SSFM DISABLED
–10
–20
–30
–40
0
SSFM ENABLED
–10
–20
–30
–40
150kHz
FREQUENCY
30MHz
(FUNDAMENTAL AND HARMONICS SHOWN)
690812 TA01b
690812fa
1