DEMO CIRCUIT 1446 DEMO CIRCUIT 1446 QUICK START GUIDE - LTC6909 QUICK START GUIDE 3 TO 8 OUTPUT MULTIPHASE OSCILLATOR WITH SSFM LTC6909 3 TO 8 OUTPUT MULTIPHASE OSCILLATOR with SSFM DESCRIPTION Demonstration circuit 1446 features the LTC6909 multi- PH2 PH1 PH0 MODE ple output oscillator with spread spectrum frequency 0 0 0 All Outputs Are Floating (Hi-Z) modulation (SSFM). The LTC6909 is an easy to use 0 0 1 All Outputs Are Held Low precision oscillator that can provide 1-, 2-, 3-, 4-, 5-, 6-, 0 1 0 3-Phase Mode (PH = 3) 7- or 8-phase synchronized outputs. The LTC6909 0 1 1 4-Phase Mode (PH = 4) spread spectrum frequency modulation (SSFM), can be 1 0 0 5-Phase Mode (PH = 5) enabled to improve electromagnetic compatibility (EMC) 1 0 1 6-Phase Mode (PH = 6) performance. Eight separate outputs provide up to eight 1 1 0 7-Phase Mode (PH = 7) rail-to-rail, 50% duty cycle clock signals. Using three 1 1 1 8-Phase Mode (PH = 8) logic inputs, the outputs are configured for phase separa- tion, ranging from 45 to 120 (three to eight phases). A DC1446 contains an LTC6909 and test terminals for The clock outputs can also be held low or configured for the eight outputs. On board jumpers are provided to set Hi-Z. A single resistor (RSET) combined with the phase the LTC6909 phase inputs (PH0, PH1 and PH2) and the configuration, sets the output frequency, based on the SSFM modulation. The on board frequency setting resis- following formula: tor (RSET) is pre-loaded with a 100k surface mount re- sistor (in addition, two pin receptacles are provided for f = (20MHz x 10k)/(RSET x PH) using a leaded RSET resistor). OUT where PH = 3, 4, 5, 6, 7 or 8 the f range is 12.5kHz to 6.67MHz. Design files for this circuit board are available. OUT Call the LTC factory. The PH0, PH1 and PH2 logic inputs define the LTC6909 LTC, LT are registered trademarks of Linear Technology Corporation. multi-phase mode of operation and control its outputs as follows: QUICK START PROCEDURE Demonstration circuit 1446 is easy to set up and test. 2. Set the power supply to 5V. Refer to Figure 1 for the quick test setup and follow the procedure below: 3. Turn on the power supply. 1. Place jumpers in the following positions: 4. With a 10x probe connected to OUT1 the oscilloscope should show a 5V, 250kHz, squarewave (4.5%). JP3 (PH0) to V+, JP4 (PH1) to V+, JP1 (PH2) to V+ and JP1 (MOD) to SSFM OFF. 1 DEMO CIRCUIT 1446 QUICK START GUIDE - LTC6909 3 TO 8 OUTPUT MULTIPHASE OSCILLATOR WITH SSFM QUICK START SET-UP Figure 1. Quick Test Setup Single Power Supply + - Oscilloscope 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).