LMK03033CISQE National Semiconductor, LMK03033CISQE Datasheet - Page 22

• Manufacturer Part Number: LMK03033CISQE
• Manufacturer: National Semiconductor

Specifications of LMK03033CISQE

• Lead Free Status / Rohs Status: Not Compliant

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3.4 LOOP FILTER
The internal charge pump is directly connected to the inte-
grated loop filter components. The first and second pole of the
loop filter are externally attached as shown in
the loop filter is designed, it must be stable over the entire
frequency band, meaning that the changes in K
low to high band specification will not make the loop filter un-
stable. The design of the loop filter is application specific and
can be rather involved, but is discussed in depth in the Clock
Conditioner Owner's Manual provided by National Semicon-
ductor. When designing with the integrated loop filter of the
LMK03000 family, considerations for minimum resistor ther-
mal noise often lead one to the decision to design for the
minimum value for integrated resistors, R3 and R4. Both the
Figure
Vtune
4. When
from the
FIGURE 4. Loop Filter
22
integrated loop filter resistors and capacitors (C3 and C4) also
restrict how wide the loop bandwidth the PLL can have. How-
ever, these integrated components do have the advantage
that they are closer to the VCO and can therefore filter out
some noise and spurs better than external components. For
this reason, a common strategy is to minimize the internal
loop filter resistors and then design for the largest internal ca-
pacitor values that permit a wide enough loop bandwidth. In
some situations where spurs requirements are very stringent
and there is margin on phase noise, it might make sense to
design for a loop filter with integrated resistor values that are
larger than their minimum value.
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