Linear Technology 1446 Quick Start Manual

DEMO CIRCUIT 1446 QUICK START GUIDE - 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:
f = (20MHz x 10k)/(RSET x PH)
OUT
where PH = 3, 4, 5, 6, 7 or 8
the f range is 12.5kHz to 6.67MHz.
OUT
The PH0, PH1 and PH2 logic inputs define the LTC6909
multi-phase mode of operation and control its outputs as
follows:
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:
1. Place jumpers in the following positions:
JP3 (PH0) to V+, JP4 (PH1) to V+, JP1 (PH2) to V+ and
JP1 (MOD) to SSFM OFF.
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3 TO 8 OUTPUT MULTIPHASE OSCILLATOR with SSFM
DEMO CIRCUIT 1446
QUICK START GUIDE
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.
2. Set the power supply to 5V.
3. Turn on the power supply.
4. With a 10x probe connected to OUT1 the oscilloscope
should show a 5V, 250kHz, squarewave (±4.5%).
LTC6909
1