Colpits blocking cap value for MC9S12DP256

[kevinhuffman]

Freescale recommends use of a blocking cap with the MC9S12DP256 Colpits clock circuit.  The cap blocks DC voltage between Extal and the crystal.  It is referred to as C11 in the Developer User's Guide (V2.05).  What is a recommended value for C11 if the device is using a 16 MHz crystal with 18 pF caps?  Apparently this cap is recommended to limit DC voltage applied to the crystal (thereby reducing crystal life expectancy) and minimizing startup issues.

[kevinhuffman]

Perfect.  Thanks for the reply.  The Freescale documentation refers back to the crystal manufacturer for the correct value of a blocking cap.  This cap value doesn't appear to be addressed on ay crystal datasheets that I looked at.  I'll proceed with the 10 nF and see what happens.

[kef · Accepted solution]

Impedance of 10nF cap at 16MHz is less than 1 Ohm...