LTC6902_15 Datasheet, PDF (1/16 Pages) Linear Technology – Multiphase Oscillator with Spread Spectrum Frequency Modulation

FEATURES
s _{2-, 3- or 4-Phase Outputs}
s _{Optional Spread Spectrum Frequency Modulation}
for Improved EMC Performance
s _{5kHz to 20MHz Frequency Range}
s _{One External Resistor Sets the Frequency}
s _{One External Resistor Sets Percent Frequency}
Spreading
s _{400µA Typical Supply Current, VS = 3V, 1MHz}
s _{Frequency Error ≤1.5% Max, 5kHz to 10MHz}
(T_A = 25°C)
s _{Frequency Error ≤ 2% Max, 5kHz to 10MHz}
(T_A = 0°C to 70°C)
s _{±40ppm/°C Temperature Stability}
s _{Fast Start-Up Time: 50µs to 1.5ms}
s _{100Ω CMOS Output Driver}
s _{Operates from a Single 2.7V to 5.5V Supply}
s _{Available in 10-Lead MS Package}
U
APPLICATIO S
s _{Switching Power Supply Clock Reference}
s _{Portable and Battery-Powered Equipment}
s _PDAs
s _{Cell Phones}
s _{Clocking Switched Capacitor Filters}
LTC6902
Multiphase Oscillator
with Spread Spectrum
Frequency Modulation
DESCRIPTIO
The LTC^®6902 is a precision, low power and easy-to-use
oscillator that provides multiphase outputs in a small
package. The oscillator frequency is set by a single exter-
nal resistor (R_SET). The LTC6902 also provides an optional
spread spectrum frequency modulation (SSFM) capability
that can be activated and controlled by an additional
external resistor (R_MOD).
The LTC6902’s master oscillator is controlled by the R_SET
resistor and has a range of 100kHz and 20MHz. In order
to accommodate a wider output frequency range, a pro-
grammable divider (divide by 1, 10 or 100) is included.
The integrated programmable multiphase circuit pro-
vides either 2-, 3- or 4-phase waveforms.
The LTC6902’s SSFM capability modulates the oscillator’s
frequency by a pseudorandom noise (PRN) signal to
spread the oscillator’s energy over a wide frequency band.
This spreading decreases the peak electromagnetic radia-
tion level and improves electromagnetic compatibility
(EMC) performance. The amount of frequency spreading
is programmable by a single additional external resistor
(R_MOD) and is disabled by grounding the MOD pin.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
500kHz, 4-Phase Clock with 20% Frequency Spreading
5V
0.1µF
R_MOD 10k
R_SET 10k
OPEN
LTC6902
V⁺
SET
DIV MOD
PH GND
OUT1 OUT4
OUT2 OUT3
OUT4
OUT3
OUT2
OUT1
6902 TA01
Output Frequency Spectrum With and Without SSFM
0
–20
OUTPUT
–40
SPECTRUM
WITH 20%
SPREADING
–60
OUTPUT
SPECTRUM
WITH SSFM
DISABLED
–80
–100
400
450 500 550
FREQUENCY (kHz)
600
6902 TA02
6902f
1