5P49V5925_16 Datasheet, PDF (7/27 Pages) Integrated Device Technology – Programmable Clock Generator

Example 1: The crystal load capacitance is specified as 8pF
and the stray capacitance at each crystal pin is Cs=1.5pF.
Assuming equal capacitance value at XIN and XOUT, the
equation is as follows:
8pF = (9pF + 0.5pF × XTAL[5:0] + 1.5pF) / 2 →
0.5pF × XTAL[5:0] = 5.5pF → XTAL[5:0] = 11 (decimal)
Example 2: The crystal load capacitance is specified as 12pF
and the stray capacitance Cs is unknown. Footprints for
external capacitors Ce are added and a worst case Cs of 5pF
is used. For now we use Cs + Ce = 5pF and the right value for
Ce can be determined later to make 5pF together with Cs.
12pF = (9pF + 0.5pF × XTAL[5:0] + 5pF) / 2 →
XTAL[5:0] = 20 (decimal)
Manual Switchover Mode
When SM[1:0] is “0x”, the redundant inputs are in manual
switchover mode. In this mode, CLKSEL pin is used to switch
between the primary and secondary clock sources. The
primary and secondary clock source setting is determined by
the PRIMSRC bit. During the switchover, no glitches will occur
at the output of the device, although there may be frequency
and phase drift, depending on the exact phase and frequency
relationship between the primary and secondary clocks.
5P49V5925 DATASHEET
NOVEMBER 11, 2016
7
PROGRAMMABLE CLOCK GENERATOR