Detailed description – Rainbow Electronics MAX31D80 User Manual
Page 6
Spread-Spectrum Clock Generators
MAX31C80/MAX31D80
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Detailed Description
The MAX31C80/MAX31D80 modulate an input clock to
generate a center-dithered or down-dithered spread-
spectrum output. An 8MHz to 27MHz crystal or 8MHz
to 134MHz oscillator input is applied to the device. An
internal PLL dithers the output clock at a user-select-
able magnitude to produce a down-dithered or center-
dithered output clock. The output clock’s frequency is
programmable from 2MHz to 134MHz. The devices also
buffer the incoming clock and provide this output on a
separate pin.
Spread-Spectrum Dither Magnitude
The MAX31D80 can generate down-dithered magnitudes
up to -3%. The MAX31C80 can generate center-dithered
magnitudes up to P 1.5%. The desired magnitude is
selected using the input pins SMSEL1 and SMSEL0 as
shown in Tables 1 and 2. A power cycle is required after
each change of the dither magnitude for the changes to
take effect.
Table_1._Spread-Spectrum_Mode_and_Magnitude_Select_(for_Down_Dither)
Table_2._Spread-Spectrum_Mode_and_Magnitude_Select_(for_Center_Dither)
SMSEL1
SMSEL0
SPREAD-SPECTRUM_MAGNITUDE_
SELECTED_(%)
SPREAD-SPECTRUM_DITHER_MODE_
SELECTED
0
0
Spread-Spectrum Disabled
0
Unconnected
0 to -0.25
Down Dither
0
1
0 to -0.375
Unconnected
0
0 to -0.5
Unconnected
Unconnected
0 to -0.75
Unconnected
1
0 to -1.0
1
0
0 to -1.5
1
Unconnected
0 to -2.0
1
1
0 to -3.0
SMSEL1
SMSEL0
SPREAD-SPECTRUM_MAGNITUDE_
SELECTED_(%)
SPREAD-SPECTRUM_DITHER_MODE_
SELECTED
0
0
Spread-Spectrum Disabled
0
Unconnected
-0.25 to +0.25
Center Dither
0
1
-0.375 to +0.375
Unconnected
0
-0.5 to +0.5
Unconnected
Unconnected
-0.75 to +0.75
Unconnected
1
-1.0 to +1.0
1
0
-1.5 to +1.5
1
Unconnected
N/A
1
1
N/A