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| LTC6902_15 Datasheet, PDF (5/16 Pages) Linear Technology – Multiphase Oscillator with Spread Spectrum Frequency Modulation | |||
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TYPICAL PERFOR A CE CHARACTERISTICS
Output Operating at 20MHz,
VS = 5V
V+ = 5V, RSET = 10k, CL = 10pF
Output Operating at 10MHz,
VS = 3V
V+ = 3V, RSET = 20k, CL = 10pF
LTC6902
1V/DIV
0V
12.5ns/DIV
69012 G06
1V/DIV
0V
25ns/DIV
69012 G07
QUICK DESIG GUIDE
V+
0.1µF
RMOD
RSET
LTC6902
V+
SET
DIV
DIV MOD
PH
PH GND
OUT1 OUT4
OUT2 OUT3
OUT4
OUT3
OUT2
OUT1
6902 F01
fOUT
=
10MHz
Nâ¢M
â¢

ï£ï£¬
20k⦠
RSET 
;
5kHz
â¤
fOUT
â¤
20MHz
Spreading Percentage = 20 ⢠RSET
RMOD
Figure 1. Typical Application with Design Equation
Step 1. Select Multiphase Mode, Setting M
By selecting the multiphase mode, a division parameter M
is also chosen:
2-Phase: Connect PH Pin to GND
3-Phase: Leave PH Open
4-Phase: Connect PH Pin to V+
M=1
M=3
M=4
Step 2. Choosing Programmable Divider Setting N
A. For applications using spread spectrum frequency
modulation (SSFM) or applications that are constant fre-
quency where low clock jitter is the primary specification:
DIVIDER SETTING
FREQUENCY RANGE (fOUT ⢠M)
N=1
Connect DIV Pin to GND
2MHz to 20MHz
N = 10 Leave DIV Open
N = 100 Connect DIV Pin to V+
200kHz to 2MHz
< 200kHz
Note: The frequency range numbers are for a 5V supply where a 20MHz
output is the maximum frequency supported. For low supply applications
(2.7V ⤠V+ ⤠4V), the maximum rated output frequency is 10MHz and all
of the above numbers should be halved.
B. For constant frequency applications where frequency
accuracy is the primary specification:
DIVIDER SETTING
FREQUENCY RANGE (fOUT ⢠M)
N=1
Connect DIV Pin to GND
> 500kHz*
N = 10 Leave DIV Open
N = 100 Connect DIV Pin to V+
50kHz to 500kHz
< 50kHz
*The maximum frequency (fOUT ⢠M) is 20MHz for 5V applications and is
10MHz for low supply applications (2.7V ⤠V+ ⤠4V).
6902f
5
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