0
\$\begingroup\$

I need a replacement part for this 514MCC001237AAGR part in this reference design.

I'm sorry if this is a noob question. Can I replace 514MCC001237AAGR which has a frequency of 25 MHz with 514CBC001037BAG which has a frequency of 24.576 MHz?

Another thing is that the original part has an output of CMOS, Dual (In-Phase) that I cannot understand. The 514CBC001037BAG has an output of CMOS but isn't Dual (In-Phase), what would be the effect of it in the circuit?

Thank you so much.

\$\endgroup\$
3
  • 2
    \$\begingroup\$ Why would you pick a different frequency? It's usually critical even if just used to clock some MCU. If said MCU relies on serial buses etc then all baudrate settings will get affected. \$\endgroup\$
    – Lundin
    Commented Jan 4, 2022 at 9:53
  • \$\begingroup\$ I'd suggest you ask Analog Devices. These clock generators are programmable via I2C and the different part numbers are for the default freq and output configuration. The question is does the Analog Devices code reconfigure them from the factory config? \$\endgroup\$
    – Kartman
    Commented Jan 4, 2022 at 10:02
  • 1
    \$\begingroup\$ Depends what the design is. On a musical instrument, you'll be out of tune. Ethernet PHY? It won't talk to anybody else out there except another board with the same change. \$\endgroup\$
    – user16324
    Commented Jan 4, 2022 at 14:25

3 Answers 3

5
\$\begingroup\$

The reference design link you give is an Analog Devices circuit note for an Ethernet PHY. On p4, that states:

Programmable MAC Interface Clock The ADIN1300 has three MAC interface options, MII, RMII or RGMII. For RGMII and MII interfaces, a 25 MHz clock is required for the ADIN1300, while the RMII requires an external 50 MHz clock. In a user application, a user can choose to place a 25 MHz crystal close to the XTAL_I and XTAL_O pins, or for the RMII use case, the host controller, MAC interface, or switch can provide the required 50 MHz clock directly to the PHY.

So: no, according to that document, the crystal cannot be 24.576 MHz. Use 25 MHz instead.

Beyond that document, an Ethernet PHY requires an accurate and stable 25 MHz clock to drive PLLs that produce timing clocks for the LAN communications. Your PHY can handle the 10 Mbps, 100 Mbps and 1000 Mbps. If you change the crystal to 24.576 MHz, the PHY will not produce these speeds for communication on a network.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Worth noting that the device is not simply a crystal, but a synthesized oscillator. It looks like the frequency can be selected via I2C. \$\endgroup\$
    – Kartman
    Commented Jan 4, 2022 at 11:55
1
\$\begingroup\$

The only 1 objective of the oscillators is to provide clock pulses to the internal working circuitry. Changing the frequency will change the time period of the clock pulses and thus chip will start malfunctioning which includes destroying data communication by sending garbage (specifically at higher speeds) as well as any timing functions performed inside the chip. I would strictly recommend you to use 25MHz oscillator.

\$\endgroup\$
1
\$\begingroup\$

It depends why the crystal is being used. Does the application merely require a stable frequency, or does it require a stable and accurate frequency.

If you were clocking a random MCU that had to blink LEDs, then pretty much any frequency up to its maximum would do.

If you are clocking something that has to work with other equipment at a specific speed, then you need the right frequency. As your application is ethernet, you need the right frequency.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.