Hello team,
I received a question from my customer about the capacitor configuration for the OSC of PHY.
The 9.2.1.2 Clock in (XI) Recommendation in the DP83867IR data sheet contains the oscillator connection guidelines.
"If an external clock source is used, XO should be left floating. For a 1.8-V clock source, XI should be tied to the clock source. For a 3.3-V or 2.5-V clock source, A capacitor divider is recommended as shown in Figure 32. For a 3.3-V clock source, The CD1 and CD2 capabilities used are recommended to be 27 pF. If a 2.5-V clock source is used check with the vendor for recommended capacitor loads. The values of CD1 and CD2 shall be adjusted to meet XI Input pin specification defined in Electrical Characteristics"
It is recommended to use 27pF for CD1 and CD2 with a 3.3V clock source, but I couldn't understand the description about 2.5V.
- Could you tell me how to select and calculate capacitors when using 2.5V?
Our system will have a high OSC output of Min 0.9VCC and a load capacity of max15pF.
Therefore, the OSC output high voltage level is 2.25V-2.5V, which exceeds the Phy input (XI) Max specification of 2.1V.
Best Regards,
Ryotaro Fukui
