Si5345-44-42-D-RM
Rev. 1.0
11
3. DSPLL and MultiSynth
The DSPLL is responsible for input frequency translation, jitter attenuation and wander filtering. Fractional input
dividers (Pxn/Pxd) allow the DSPLL to perform hitless switching between input clocks (INx) that are fractionally
related. Input switching is controlled manually or automatically using an internal state machine. The oscillator
circuit (OSC) provides a frequency reference which determines output frequency stability and accuracy while the
device is in free-run or holdover mode. Note that a XTAL (or suitable XO reference on XA/XB) is always required
and is the jitter reference for the device. The high-performance MultiSynth dividers (Nxn/Nxd) generate integer or
fractionally related output frequencies for the output stage. A crosspoint switch connects any of the MultiSynth
generated frequencies to any of the outputs. A single MultiSynth output can connect to two or more output drivers.
Additional integer division (R) determines the final output frequency as shown in Figure 2.
Figure 2. Si5342 DSPLL and Multisynth System Flow Diagram
The frequency configuration of the DSPLL is programmable through the SPI or I
2
C serial interface and can also be
stored in non-volatile memory or RAM. The combination of fractional input dividers (Pn/Pd), fractional frequency
multiplication (Mn/Md), fractional output MultiSynth division (Nn/Nd), and integer output division (Rn) allows the
generation of virtually any output frequency on any of the outputs. All divider values for a specific frequency plan
are easily determined using the
ClockBuilder Pro software
.
IN_SEL[1:0]
DSPLL
LPF
PD
Optional
External
Feedback
VDDO0
OUT0
OUT0
OUT1
VDDO1
OUT1
÷R
1
÷R
0
Multi
Synth
÷ N
0n
N
0d
Multi
Synth
÷ N
1n
N
1d
t
0
t
1
IN0
IN0
IN1
IN1
÷ P
0n
P
0d
÷ P
1n
P
1d
IN2
IN2
IN3/FB_IN
IN3/FB_IN
÷ P
3n
P
3d
÷ P
2n
P
2d
÷
M
n
M
d
48-54MHz XTAL
or REFCLK
OSC
XB
XA
÷PXAXB