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If the frequency stability over a temperature range is not a concern in a project instead it's reliability in continuous long time operation is a more important factor then which of the two oscillators would be preferable, internal RC (16 MHz) or general purpose external crystal oscillator (8 MHz) to get a SysClk of 160 MHz using the internal PLL?

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If reliability is your only concern then you should avoid adding components and connections to your system. All other factors being equal, an internal clock source will have greater long term reliability than an external clock source that requires additional components.

However, you need to be very certain that the frequency accuracy and stability are acceptable for your application.

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    \$\begingroup\$ Not to mention that as reliable as quartz crystals are, they are mechanical components and are among the most unreliable components in electronics. They are vulnerable to shock damage and an an RC oscillator is much more reliable. The advantage of a crystal is stability and accuracy, not reliability. \$\endgroup\$ – DKNguyen Feb 23 at 21:35
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    \$\begingroup\$ Additionally, the internal oscillator reliability is better than the reliability of the chip, which is specified in the datasheet. Reliability of external crystal, capacitors, pcb design, pcb traces, solder, soldering technique used etc. is unknown unless tested. \$\endgroup\$ – Indraneel Feb 23 at 21:43
  • \$\begingroup\$ How accurate must that 160MHz be, after 10 or 20 years? \$\endgroup\$ – analogsystemsrf Feb 24 at 2:29

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