Intel Ethernet Controller I210-AT oscillator AC coupling capacitor value

[ShadyG]

Hello,

We are using Intel Ethernet Controller I210-AT in our design. We are the OEM.

We chose to use an oscillator for the clock input. Figure 11-9 from page 800 of the I210_Datasheet_v_3.7 document (page 796 of the pdf) is copied below and shows two values for the oscillator AC coupling capacitor: "C1 = 100pF or 51pF." It is confusing that two different values are given for C1.
Does each C1 capacitance value (100pF or 51pF) correspond to one of the shown VCC voltages: "VCC = 2.5V or 3.3V?" or can either capacitance value be used with either VCC voltage?

What value should C1 be for a 3.3V oscillator?

Link to the datasheet:

https://www.intel.com/content/www/us/en/content-details/333016/intel-ethernet-controller-i210-datasheet.html?wapkw=i210%20datasheet

Thank you.

[CarlosAM_INTEL]

Hello, @ShadyG:

Thank you for contacting Intel Embedded Community.

We sent an email to the address associated with this account with information that may help you.

Best regards,

@CarlosAM_INTEL.

[Diego_INTEL · Accepted solution]

Hello @ShadyG,

Thank you for contacting Intel Embedded Community.

I have verified internally and the recommended value when using 3.3 V is C1 = 51 pF, you only have to verify that the XTAL1 value has an amplitude of 1.7 V or close to it.

Best regards,

@Diego_INTEL 

[ShadyG]

Hello @Diego_INTEL ,

Thank you for your response.

I just probed multiple channels that we prototyped with each C1 value (51 pF and 100 pF) for evaluation. Here are the minimum and maximum XTAL1 voltage levels with each capacitance value:

• C1 = 51 pF
  • Min = -0.24 V
  • Max = 1.3 V
• C1 = 100 pF
  • Min = -0.24 V
  • Max = 1.84 V

Based on my measurements, it seems that 100 pF better meets the 1.7 V amplitude.

Do you have any other feedback based on my above measurements?

Best regards,

Shady

[Diego_INTEL]

Hello @ShadyG,

It seems it depends on the design as you get different values with 51 pF than with other results I looked, but you can try a value between to get closer to 1.7 V.

My apologies for the late reply, it seems I forgot to submit the answer but got the answer saved.

Best regards,

@Diego_INTEL