sy89538l Micrel Semiconductor, sy89538l Datasheet - Page 16

• Manufacturer Part Number: sy89538l
• Description: Sy89538l 3.3v Precision Lvpecl And Lvds Programmable Multiple Output Bank Clock
• Manufacturer: Micrel Semiconductor

External Loop Filter Considerations
The SY89538L features an external PLL loop filter
that allows the users to tailor the PLL’s behavior. It is
recommended that ceramic capacitors with NPO or
X7R dielectric be used, since they have very low
effective series resistance. For applications that
require
components shown in Figure 4. Larger values of the
zero capacitor (capacitor shown in parallel) results in
less cycle-to- cycle jitter, however the total jitter
increases as the value of the zero capacitor
increases.
increases, loop stability decreases as the zero
capacitor begins to dominate over the pole capacitor
(capacitor in series with the damping resistor). The
external loop filter allows the user to change the loop
filter values for specific jitter requirements. Using a
smaller resistor in the loop filter decreases the PLL’s
loop bandwidth. This results in less noise from the
PLL input, but potentially more noise from the VCO.
Take care to keep the loop filter components on the
same side of the board and as close as possible to
the SY89538L’s LR and LF pins. To minimize noise
pick up on the loop filter pins, cut the ground plane
directly underneath the loop filter component pads
and traces. However, the benefit may not be
significant in all applications.
January 2008
ultra-low
In
addition,
Figure 4. Loop Filter
cycle-to-cycle
as
the
jitter,
zero
use
capacitor
the
16
Power Supply Filtering Techniques
As with any high-speed integrated circuit, power
supply filtering is very important. At a minimum,
VCCA, VCCD, and all VCCO pins should be
individually connected using a via to the power supply
plane, and separate bypass capacitors should be
used for each pin. To achieve optimal jitter
performance, each power supply pin should use
separate instances of the circuit shown in Figure 5.
Note:
For V
BLM21A1025.
For V
CCA
CCO
and V
use ferrite bead3A, 0.025Ω DC, Murata, P/N BLM31P005.
CCD
use ferrite bead, 200mA, Murata P/N
Figure 5. Recommended
Power Supply Filter
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