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Si5341/40
Preliminary Rev. 0.9
21
4. Functional Description
The Si5341/40 combines a wide band PLL with next
generation MultiSynth technology to offer the industry’s
most versatile and high performance clock generator.
The PLL locks to either an external crystal (XA/XB) for
generating free-running clocks or to an external clock
(IN0 - IN2) for generating synchronous clocks. In free-
run mode the oscillator frequency is multiplied by the
PLL and fractionally divided by the MultiSynth stage to
any frequency in the range of 100 Hz to 800 MHz per
output. In synchronous mode, any clock frequency at
the input pins in the range of 10 MHz to 750 MHz can
be multiplied to generate any output frequency from
100 Hz to 800 MHz on each output.
The high-resolution fractional MultiSynth™ dividers
enables true any-frequency input to any-frequency on
any of the outputs. The output drivers offer flexible
output formats which are independently configurable on
each of the outputs. This clock generator is fully
configurable via its serial interface (I
2
C/SPI) and
includes in-circuit programmable non-volatile memory.
4.1. Modes of Operation
The Si5341/40 supports both free-run and synchronous
modes of operation. Mode selection is manually
selected through input pins (IN_SEL0/1) or through the
serial interface by writing to the input select register
(IN_SEL, 0x21[2:1]). Pin selection is set by default. A
state diagram showing the modes of operation is shown
in Figure 6.
Figure 6. Si5341 Initialization and Modes of Operation
Power-Up
Serial interface
ready
RST
pin asserted
Hard Reset
bit asserted
XTAL/XO
Connected to
XA/XB pins?
Yes
No
XA/XB
No Output Clocks
Generated
Synchronous Mode
Output Clocks
Generated at
Configured
Frequencies Based
on Input Clock
Frequency Accuracy
Input
Selected?
XA/XB
Free-run Mode
Output Clocks
Generated at
Configured
Frequencies Based
on XTAL Frequency
Accuracy
Synchronous Mode
Output Clocks
Generated at
Configured
Frequencies Based
on Input Clock
Frequency Accuracy
Input
Selected?
IN0, IN1,
IN2
IN0, IN1,
IN2
Synchronous or
Free-run
Operation
Synchronous
Operation
Initialization
NVM download
Soft Reset
bit asserted