SI514 Datasheet, PDF (12/36 Pages) Silicon Laboratories – ANY-FREQUENCY IC PROGRAMMABLE XO

Si514
2. Functional Description
The Si514 offers system designers a programmable, low jitter XO solution with exceptionally fine frequency tuning
resolution. To enable designers to take full advantage of this flexibility and performance, Silicon Laboratories
provides an easy-to-use evaluation kit and intuitive suite of Windows-based software utilities to simplify the Si514
programming process.
The Si5xx-PROG-EVB kit contains the Programmable Oscillator Software suite and an EVB Driver (USBXpress^®)
for use with USB-equipped PCs. Go to
http://www.silabs.com/products/clocksoscillators/Pages/DevelopmentTools.aspx for more information.
Alternatively, “2.1. Programming a New Output Frequency” provides designers a detailed description, along with
examples, of the frequency programming requirements and process for designers who are interested in learning
more about the programming algorithms implemented within the Programmable Oscillator Software suite.
2.1. Programming a New Output Frequency
The output frequency (Fout) is determined by programming the feedback multiplier (M=M_Int.M_Frac), High-
Speed Divider (HS_DIV), and Low-Speed Divider (LS_DIV) according to the following formula:
F_out = _H-----_S-----_{_}---_D-^F---_I-^X-_V---^O--_---^--_L---^M-_S----_{_}----_D----_I--_V--
where F_XO = 31.98MHz
Figure 1. Block Diagram of Si514
The value of the feedback multiplier M is adjustable in the following range:
 65.04065041  M  78.17385866.
This keeps the VCO frequency within the range of 2080 MHz  F_VCO  2500 MHz, since the VCO frequency is the
product of the internal fixed-frequency crystal (F_XO) and the high-resolution 29-bit fractional multiplier (M). This 29-
bit resolution of M allows the VCO frequency to have a frequency tuning resolution of 0.026 ppb.
The device comes from the factory with a pre-programmed center frequency within the range of
100 kHz  F_OUT  250 MHz, as specified by the 6-digit code in the part number. (See section “6. Ordering
Information” for more information.) To change from the factory-programmed frequency to a different value, the user
must follow one of two algorithms based on the magnitude of the frequency change.
 “Small Frequency Change.” To change the frequency by < ±1000 ppm, the user must keep the same center
frequency and only update the value of M. Refer to section "2.2. Programming a Small Frequency Change (sub
±1000 ppm)" on page 13.
 “Large Frequency Change.” To change the frequency by ±1000 ppm, the user must change the center
frequency. This may require updates to the output dividers (HS_DIV and/or LS_DIV) and possibly the LP1 and
12
Rev. 1.0