LTC6945 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC6945' PDF : 28 Pages View PDF
LTC6945
APPLICATIONS INFORMATION
resistance (see Figure 22 for an example). See QFN Pack-
age Users Guide, page 8, on Linear Technology website’s
Packaging Information page for specific recommendations
concerning land patterns and land via solder masks. Links
are provided below.
http://www.linear.com/designtools/packaging/index.jsp
REFERENCE SIGNAL ROUTING AND SPURIOUS
The charge pump operates at the PFD’s update frequency
fPFD. The resultant output spurious energy is small and
is further reduced by the loop filter before it modulates
the VCO frequency.
However, improper PCB layout can degrade the LTC6945’s
inherent spurious performance. Care must be taken to
prevent the reference signal fREF from coupling onto the
VCO’s tune line, or into other loop filter signals. Example
suggestions are the following.
1. Do not share power supply decoupling capacitors
between same voltage power supply pins.
2. Use separate ground vias for each power supply de-
coupling capacitor, especially those connected to VREF+,
VCP+, and VVCO+.
3. Physically separate the reference frequency signal from
the loop filter and VCO.
6945 F22
Figure 22. Example Exposed Pad Land Pattern
6945f
25
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