I'd like to drive an Si5350 with a MEMS oscillator instead of a crystal for environmental robustness purposes. The Si5350 FAQ says that a CMOS input may be used instead of a crystal so long as the input does not exceed 1 Vpp. The MEMS oscillators are only available in 2.5V - 3.3V outputs.

Is a voltage divider an acceptable means of reducing the input reference, or is there a better solution?

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    \$\begingroup\$ Data sheet link for the Si5350 would help. \$\endgroup\$
    – Andy aka
    Commented Oct 6, 2020 at 16:37
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    \$\begingroup\$ what is the switching frequency? you can use a 1N4148 (switching diode) to reduce the voltage, use 2 such diodes with MEMS of 2.5V to reduce the voltage level. \$\endgroup\$
    – Deepak
    Commented Oct 6, 2020 at 16:38
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    \$\begingroup\$ Data sheet not FAQ. \$\endgroup\$
    – Andy aka
    Commented Oct 6, 2020 at 17:00
  • \$\begingroup\$ Your MEMS oscillator may require a specified load capacitance. Be aware that Si535x has configurable internal capacitors meant for its xtal-oscillator. These can be set for 0,6,8,10 pf. Use XA input rather than XB input. \$\endgroup\$
    – glen_geek
    Commented Oct 6, 2020 at 17:09
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    \$\begingroup\$ Why not use an Si5351C, which is designed with a proper clkin input? \$\endgroup\$
    – TimWescott
    Commented Oct 6, 2020 at 17:33

1 Answer 1


Use the SI5350B which supports VCXO directly (but datatsheet doesn't say how) or

enter image description here Source: https://www.silabs.com/content/usergenerated/asi/cloud/attachments/siliconlabs/en/community/groups/timing/knowledge-base/_jcr_content/content/primary/blog/si5350_si5351_faq-1Xj5/Si5350-Si5351%20FAQ%20(v0.5).pdf


this circuit with the SI5350A (which is a bit weird that they've capacitivly coupled the clock):
enter image description here
Source: https://www.silabs.com/documents/public/data-sheets/Si5350A-B.pdf

I would double check with Si before implementing an CMOS input as there is little info on the voltage limits of the pin or the internals for the clock.


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