SI5356A Datasheet, PDF (16/29 Pages) Silicon Laboratories – IC PROGRAMMABLE, ANY-FREQUENCY 1–200 MHZ, QUAD FREQUENCY 8-OUTPUT CLOCK GENERATOR

Si5356A
S Slv Addr [6:0] 0 A Reg Addr [7:0] A S Slv Addr [6:0] 1 A Data [7:0] A Data [7:0] N P
Repeated Start Read
Optional
S Slv Addr [6:0] 0 A Reg Addr [7:0] A P
S Slv Addr [6:0] 1 A Data [7:0]
Write Data
Two Command Read
Read Data
A Data [7:0] N P
Optional
S Slv Addr [6:0] 0 A Reg Addr [7:0] A Data [7:0] A Data [7:0] A P
Write
Optional
From master to slave
From slave to master
1 – Read
0 – Write
A – Acknowledge (SDA LOW)
N – Not Acknowledge (SDA HIGH).
Required after the last data byte to signal the end of the read comand to the slave.
S – START condition
P – STOP condition
Figure 8. I²C/SMBus-Compatible Command Format
3.11. Spread Spectrum
To help reduce electromagnetic interference (EMI), the
Si5356A supports spread spectrum modulation. The
output clock frequencies can be modulated to spread
energy across a broader range of frequencies, lowering
system EMI. The Si5356A implements spread spectrum
using its patented MultiSynth technology to achieve
previously unattainable precision in both modulation
rate and spreading magnitude as shown in Figure 9.
Through I²C control, the Spread Spectrum can be
applied to any output clock, any clock frequency, and
any spread amount from ±0.1% to ±2.5% center spread
and –0.1% to –5% down spread .
The spreading rate is limited to 30 to 63 kHz.
The Spread Spectrum is generated digitally in the output
MultiSynths which means that the Spread Spectrum
parameters are virtually independent of process,
voltage, and temperature variations. Since the Spread
Spectrum is created in the output MultiSynths, through
I²C each output channel can have independent Spread
Spectrum parameters. Without the use of I²C (NVM
download only) the only supported Spread Spectrum
parameters are for PCI Express compliance composing
100 MHz clock, 31.5 kHz spreading frequency with the
choice of the spreading.
Rev A devices provide native support for both down and
center spread. Center spread is supported in rev B
devices by up-shifting the nominal frequency and using
down-spread register parameters. Consult AN565 for
details.
Note: If you currently use center spread on a revision A and
would like to migrate to a revision B device, you must
generate a new register map using either ClockBuilder
Desktop or the equations in AN565. Center spread
configurations for
Revisions A and B are not compatible.
16
Rev. 1.3