Si5350C-B

Rev. 1.0

11

4. Configuring the Si5350C

The Si5350C is a factory-programmed custom clock generator that is user definable with a simple to use web-

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

load capacitance requirements are supported using additional external load capacitance

pF capacitors on XA and XB) as shown in Figure 5.

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).

XA

XB

Optional internal

load capacitance

0, 6, 8,10 pF

Optional additional

external load

capacitance

(< 2 pF)