si5350a Silicon Laboratories, si5350a Datasheet - Page 9

• Manufacturer Part Number: si5350a
• Description: Factory-programmable Any-frequency Cmos Clock Generator
• Manufacturer: Silicon Laboratories

4. Configuring the Si5350A
The Si5350A is a factory-programmed custom clock generator that is user definable with a simple to use web-
based utility (www.silabs.com/ClockBuilder). The ClockBuilder utility provides a simple graphical interface that
allows the user to enter input and output frequencies along with other custom features as described in the following
sections. All synthesis calculations are automatically performed by ClockBuilder to ensure an optimum
configuration. A unique part number is assigned to each custom configuration.
4.1. Crystal Inputs (XA, XB)
The Si5350A uses a fixed-frequency standard AT-cut crystal as a reference to synthesize its output clocks.
4.1.1. Crystal Frequency
The Si5350A can operate using either a 27 MHz or a 25 MHz crystal.
4.1.2. Internal XTAL Load Capacitors
Internal load capacitors (C
to the Si5350A. Options for internal load capacitors are 6, 8, or 10 pF, or no internal load capacitors. XTALs with
alternate load capacitance requirements are supported using external load capacitors as shown in Figure 3.
4.2. Output Clocks (CLK0–CLK7)
The Si5350A is orderable as a 3-output (10-MSOP) or 8-output (24-QSOP, 20-QFN) clock generator. Output clocks
CLK0 to CLK5 can be ordered with two clock frequencies (F1_x, F2_x) which are selectable with the optional
frequency select pins (FS0/1). See “4.3.3. Frequency Select (FS_0, FS_1)” for more details on the operation of the
frequency select pins.
4.2.1. Output Clock Frequency
Outputs can be configured at any frequency from 8 kHz up to 100 MHz. In addition, the device can generate any
frequency up to 125 MHz on two of its outputs.
4.2.2. .Spread Spectrum
Spread spectrum can be enabled on any of the clock outputs for reducing electromagnetic interference (EMI).
Enabling spread spectrum on an output clock modulates its frequency, which effectively reduces the overall
amplitude of its radiated energy. Up to –15 dB reduction in EMI is possible.
The Si5350A supports several levels of spread spectrum allowing the designer to chose an ideal compromise
between system performance and EMI compliance. The amount of spread is configurable within the following
parameters:

An optional spread spectrum enable pin (SSEN) is configurable to enable or disable the spread spectrum feature.
See “4.3.1. Spread Spectrum Enable (SSEN)” for details.
Down spread: –0.5 to –2.5% modulation amplitude
Figure 3. External XTAL with Optional Load Capacitors
L
) are provided to eliminate the need for external components when connecting a XTAL
Optional external
load capacitors
C
C
L
L
XA
XB
C
L
Rev. 0.2
C
L
Optional internal
load capacitors
6pF, 8pF, 10pF
Si5350A
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