LINEAR TECHNOLOGY LTC6909 3 To 8 Output Multiphase Oscillator with SSFM User Guide
- June 4, 2024
- LINEAR TECHNOLOGY
Table of Contents
LINEAR TECHNOLOGY LTC6909 3 To 8 Output Multiphase Oscillator with SSFM
DESCRIPTION
Demonstration circuit 1446 features the LTC6909 multi-ple output oscillator
with spread spectrum frequency modulation (SSFM). The LTC®6909 is an easy to
use precision oscillator that can provide 1-, 2-, 3-, 4-, 5-, 6-, 7- or
8-phase synchronized outputs. The LTC6909 spread spectrum frequency modulation
(SSFM), can be enabled to improve 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 separa-tion, 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 (RSET)
combined with the phase configuration, sets the output frequency, based on the
following formula:
fOUT = (20MHz x 10k)/(RSET x PH)
where PH = 3, 4, 5, 6, 7 or 8
the fOUT range is 12.5kHz to 6.67MHz.
The PH0, PH1 and PH2 logic inputs define the LTC6909 multi-phase mode of
operation and control its outputs as follows:
PH2 PH1 PH0 MODE
0 0 0 All Outputs Are Floating (Hi-Z)
0 0 1 All Outputs Are Held Low
0 1 0 3-Phase Mode (PH = 3)
0 1 1 4-Phase Mode (PH = 4)
1 0 0 5-Phase Mode (PH = 5)
1 0 1 6-Phase Mode (PH = 6)
1 1 0 7-Phase Mode (PH = 7)
1 1 1 8-Phase Mode (PH = 8)
A DC1446 contains an LTC6909 and test terminals for the eight outputs. On board jumpers are provided to set the LTC6909 phase inputs (PH0, PH1 and PH2) and the SSFM modulation. The on board frequency setting resis-tor (RSET) is pre-loaded with a 100k surface mount re-sistor (in addition, two pin receptacles are provided for using a leaded RSET resistor).
Design files for this circuit board are available.
Call the LTC factory. LTC, LT are registered trademarks of Linear Technology Corporation.
QUICK START PROCEDURE
Demonstration circuit 1446 is easy to set up and test. Refer to Figure 1 for the quick test setup and follow the procedure below:
-
Place jumpers in the following positions:
JP3 (PH0) to V+, JP4 (PH1) to V+, JP1 (PH2) to V+ and JP1 (MOD) to SSFM OFF. -
2. Set the power supply to 5V.
-
Turn on the power supply.
-
With a 10x probe connected to OUT1 the oscilloscope should show a 5V, 250kHz, squarewave (±4.5%).
QUICK START SET-UP
NOTE: The 6909 outputs (OUT1-OUT8) can drive 1k and 50pF loads. If a spectrum analyzer is used to measure the spread spectrum bandwidth then use a high impedance probe to monitor the outputs (typically the input impedance of a spectrum analyzer is 50 ohms).
DEMO CIRCUIT 1446 QUICK START GUIDE – LTC6909 3 TO 8 OUTPUT MULTIPHASE
OSCILLATOR WITH SSFM 
DC1446 PARTS LIST
Item Qty Reference Part Description Manufacturer / Part #
1 1 C1 CAP., X7R, 10uF, 10V, 20% 1206 AVX, 1206ZC106MAT2A
2 2 C5,C2 CAP., X7R, 0.1uF, 16V, 10% 0402 TDK, C1005X7R1C104K
3 2 C3,C6 CAP., X5R, 1uF, 6.3V, 10% 0402 TDK, C1005X5R0J105K
4 1 C4 CAP., C0G, 1000pF, 25V, 5% 0402 TDK, C1005C0G1E102J
5 2 E1,E2 JACK, BANANA KEYSTONE, 575-4
6 10 E3-E12 TESTPOINT, TURRET, .094″ pbf MILL-MAX, 2501-2-00-80-00-00-07-0
7 3 JP1,JP3,JP4 3 PIN 0.079 SINGLE ROW HEADER SAMTEC, TMM103-02-L-S
8 1 JP2 2X4, 0.079 DOUBLE ROW HEADER SAMTEC, TMM104-02-L-D
9 4 xJP1-xJP4 SHUNT, .079″ CENTER SAMTEC, 2SN-BK-G
10 0 RSET(open) Res., 0805
11 2 E13,E14 Pin, 0.057 hole Mill-Max, 8427-0-15-15-30-84-04-0
12 1 U1 IC., LTC6909CMS, MSOP-16 Linear Tech., LTC6909CMS
13 4 (STAND-OFF) STAND-OFF, NYLON 0.375″ KEYSTONE, 8832(SNAP ON)
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