3. Functional Description
The Si5397 takes advantage of Silicon Labs fourth-generation DSPLL technology to offer the industry’s most integrated and flexible
jitter attenuating clock generator solution. Each of the DSPLLs operate independently from each other and are controlled through a
common serial interface. Each DSPLL has access to any of the four inputs (IN0 to IN3) after having been divided down by the P divid-
ers, which are either fractional or integer. Clock selection can be either manual or automatic. Any of the output clocks can be configured
to any of the DSPLLs using a flexible crosspoint connection. The Si5396 is a smaller form factor dual DSPLL version with four inputs
and four outputs.
The Si5397J/K is the internal refernce version of the Si5397A/B. Si5397L/M is the internal reference version of Si5397C/D. Si5396J/K is
the internal reference version of Si5396A/B. All the features and functions are the same. The only difference is that the reference is
integrated into the package. The registers and features of the external reference parts match that of the internal reference parts.
Throughout this document the register descriptions for labels of the external reference grades can be assumed to be the same for the
internal reference grades.
3.1 DSPLL and MultiSynth
The DSPLL is responsible for input frequency translation, jitter attenuation and wander filtering. Fractional input dividers (Pxn/Pxd) al-
low for integer or fractional division of the input frequency, but the input frequencies must be integer related to allow the DSPLL to per-
form hitless switching between input clocks (INx). Input switching is controlled manually or automatically using an internal state ma-
chine. 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 refer-
ence 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 generated frequencies to any of the outputs. A single MultiSynth output can
connect to one or more output drivers. Additional integer division (R) determines the final output frequency. The internal reference
grade devices have a XTAL integrated in the package, so no external XTAL is needed. The specs for the integrated reference can be
found in the data sheet.
Si5397
DSPLL
A
DSPLL
B
DSPLL
D
DSPLL
C
IN1
IN2
IN3
IN0
OUT7
OUT6
OUT5
OUT1
OUT4
OUT3
OUT2
OUT0
÷INT
÷INT
÷INT
÷INT
÷INT
÷INT
÷INT
÷INT
÷FRAC
÷FRAC
÷FRAC
÷FRAC
Si5347C/D
NVM
I
2
C/SPI
Control/
Status
XTAL/
REFCLK
XB
XA
OSC
Si5347A/B
Si5396
DSPLL
A
DSPLL
B
IN1
IN2
IN3
IN0
OUT1
OUT3
OUT2
OUT0
÷INT
÷INT
÷INT
÷INT
÷FRAC
÷FRAC
÷FRAC
÷FRAC
NVM
I
2
C/SPI
Control/
Status
XTAL/
REFCLK
XB
XA
OSC
Figure 3.1. 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-vola-
tile memory. The combination of fractional input dividers (Pn/Pd), fractional frequency multiplication (Mn/Md), fractional output Multi-
Synth 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.
Si5397/96 Reference Manual
Functional Description
silabs.com
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