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Seamless 100kHz SYNC from external vs internal clock sources?

Terje Bohler1
Intellectual 330 points

Other Parts Discussed in Thread: LMK04906

Which TI circuit(s), if any, can we use to solve our problem to create a stable “Stable100kHz” sync clock which is input to our TMS 320F28069 (or can the TMS-DSP to the job by itself?).

 

Here is the situation/problem:

The Ext100kHz SYNC pulses may be “unstable” and disappear for a shorter or longer time. If so, the 100kHz oscillator should be selected “seamlessly” as the source for the “Stable100kHz” output sync pulses. When the Ext100kHz re-appear, that signal should again be selected “seamlessly” as the source for the “Stable100kHz” sync pulse.

Does TI have a chip/solution that solve our sync challenge described above?

Best regards
Terje Bøhler

  • TI__Mastermind 24205 points

    Hi Terje,

    We do not have a simple solution to your problem. LMK04906 could work. You would need to use a 25 MHz or 10 MHz VCXO on OSCin, the 100 kHz inputs will go on the CLKinX input pins. PLL2 will need to be setup to generate a VCO frequency, which when divided by the output divider generates a 100 kHz. The input clocks can be setup to auto switch on loss of reference. In the momentary absence of the reference clock, the VCXO control voltage will rail (high or low) and the VCXO will output a frequency that is a few ppm (parts per million) away from the nominal frequency. This would result in the 100 kHz output clock moving by the same amount of ppm in frequency which should not be a concern to the DSP. Basically, the reference switching cannot glitch the output more than the pulling range of the VCXO which is usually ~+/-100ppm.

    Regards

    Arvind Sridhar