SI5350C-B Datasheet, PDF (11/31 Pages) Silicon Laboratories – FACTORY-PROGRAMMABLE ANY-FREQUENCY CMOS CLOCK GENERATOR

Si5350C-B
4. Configuring the Si5350C
The Si5350C 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 Si5350C uses an optional fixed-frequency non-pullable standard AT-cut crystal as a reference to generate
free-running output clocks. Note that a XTAL is not required for generating synchronous clocks that are locked to
CLKIN.
4.1.1. Crystal Frequency
The Si5350C can operate using either a 25 MHz or a 27 MHz crystal.
4.1.2. Internal XTAL Load Capacitors
Internal load capacitors are provided to eliminate the need for external components when connecting a XTAL to the
Si5350C. The total internal XTAL load capacitance (C_L) can be selected to be 0, 6, 8 or 10 pF. XTALs with alternate
load capacitance requirements are supported using additional external load capacitance  2 pF (e.g., by using  4
pF capacitors on XA and XB) as shown in Figure 5.
XA
XB
Optional additional
external load
capacitance
(< 2 pF)
Optional internal
load capacitance
0, 6, 8,10 pF
Figure 5. External XTAL with Optional Load Capacitors
4.2. External Clock Input Pin (CLKIN)
The external clock input is used as a reference for generating synchronous clocks. The input frequency can be
specified from 10 to 100 MHz including fractional frequencies (e.g., 74.25 MHz x 1000/1001). The ClockBuilder
utility automatically determines the exact synthesis ratio to guarantee an output frequency with 0 ppm error with
respect to its reference.
4.3. Output Clocks (CLK0–CLK7)
The Si5350C is orderable as a 3-output (10-MSOP) or 8-output (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 “4.4.3. Frequency Select (FS_0, FS_1)” for more details on the operation of the frequency
select pins. Each output clock can select its reference for either of the PLLs.
4.3.1. Output Clock Frequency
Outputs can be configured at any frequency from 2.5 kHz up to 200 MHz. However, only two unique frequencies
above 112.5 MHz can be simultaneously output. For example, 125 MHz (CLK0), 130 MHz (CLK1), and 150 MHz
(CLKx) is not allowed. Note that multiple copies of frequencies above 112.5 MHz can be provided, for example,
125 MHz could be provided on four outputs (CLKS0-3) simultaneously with 130 MHz on four different outputs
(CLKS4-7).
Rev. 1.0
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