crystal damage

hayee · Joined: 05 Sep 2007 Posts: 252

Hi,
i am using pic16f628A with 20Mhz crystal.
i wanna know that can high gain damage crystal if resistor in the oscillator circuit is not used and the gain is high in HS and crystal is 20 Mhz.

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

Basically yes, although I didn't experience this yet. Many MHz crystals have a specification of 100 µW maximum drive level, it's easy however, to achieve 500 µW and more with usual oscillators circuits.

Microchip regards this issue apparently as other peoples problem:

Ttelmah · Guest

Generally, damage will be 'long term'. There is much more of a problem that frequency control will often go to 'pot' if such crystals are overdriven, with odd frequencies being generated, if the crystal is moving beyond it's design. This happens well before damage. At the end of the day, the PIC output, has a specified drive voltage, and if this will overdrive the crystal you have selected, you will get better performance and reliability by calculating the right resistor, and adding this.

Best Wishes