IDT5V49EE901
EEPROM PROGRAMMABLE CLOCK GENERATOR
CLOCK SYNTHESIZER
clocks are at different frequencies, the device will always
remain on the primary clock unless it is absent for two
secondary clock cycles. The secondary clock must always
run at a frequency less than or equal to the primary clock
frequency.
Q[6:0]
PM
0
Output Divider
111 1111
Disabled
1
/1
Reference Divider, Feedback Divider, and
Output Divider
<111 1111
0
/2
1
/((Q[6:0] + 2) * 2)
Each PLL incorporates a 7-bit reference divider (D[6:0]) and
a 12-bit feedback divider (N[11:0]) that allows the user to
generate four unique non-integer-related frequencies. Each
output divide supports 8-bit output-divider (PM and Q[7:0]).
The following equation governs how the output frequency is
calculated.
Note that the actual 7-bit Q-divider value has a 2 added to
the integer value Q and the outputs are routed through
another div/2 block. The output divider should never be
disabled unless the output bank will never be used during
normal operation. The output frequency range for LVTTL
outputs are from 4.9KHz to 200MHz. The output frequency
for LVPECL/LVDS/HCSL outputs range from 4.9KHz to
500MHz.
M
F *
=
FOUT
( D )
IN
(Eq. 1)
ODIV
Spread Spectrum Generation (PLL0)
Where FIN is the reference frequency, M is the total
feedback-divider value, D is the reference divider value,
ODIV is the total output-divider value, and FOUT is the
resulting output frequency.
PLL0 supports spread spectrum generation capability,
which users have the option of turning on or off. Spread
spectrum profile, frequency, and spread amplitude are fully
programmable. The programmable spread spectrum
generation parameters are TSSC[3:0], NSSC[2:0],
SS_OFFSET[5:0], SD[3:0], DITH, and X2 bits. These bits
are in the memory address from 0xAC to 0xBD for PLL0.
The spread spectrum generation on PLL0 can be
enabled/disabled using the TSSC[3:0] bits. To enable
spread spectrum, set TSSC > '0' and set NSSC[2:0],
SS_OFFSET[5:0], SD[3:0], and the A[3:0] (in the total M
value) accordingly. To disable spread spectrum generation,
set TSSC = '0'.
For PLL0,
M = 2 * N + A + 1 (for A>0)
M = 2 * N (for A = 0)
For PLL1, PLL2 and PLL3,
M = N
TSSC[3:0]
PM and Q[6:0] are the bits used to program the 8-bit
output-dividers for outputs OUT1-6. OUT0 does not have
any output divide along its path. The 8-bit output-dividers
will bypass or divide down the output banks' frequency with
even integer values ranging from 2 to 256.
These bits are used to determine the number of
phase/frequency detector cycles per spread spectrum cycle
(ssc) steps. The modulation frequency can be calculated
with the TSSC bits in conjunction with the NSSC bits. Valid
TSSC integer values for the modulation frequency range
from 5 to 14. Values of 0 - 4 and 15 should not be used.
There is the option to choose between disabling the
output-divider, utilizing a div/1, a div/2, or the 7-bit Q-divider
by using the PM bit. If the output is disabled, it will be driven
High, Low or High Impedance, depending on OEM[1:0].
Each bank, except for OUT0, has a PM bit. When disabled,
no clocks will appear at the output of the divider, but will
remain powered on. The output divides selection table is
shown below.
NSSC[2:0]
These bits are used to determine the number of
delta-encoded samples used for a single quadrant of the
spread spectrum waveform. All four quadrants of the spread
spectrum waveform are mirror images of each other. The
modulation frequency is also calculated based on the NSSC
bits in conjunction with the TSSC bits. Valid NSSC integer
IDT® EEPROM PROGRAMMABLE CLOCK GENERATOR
7
IDT5V49EE901
REV J 022310
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