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AM263P4: Using EXT_REFCLK0 as the Main Clock Source Instead of XTAL_IN/XTAL_OUT on AM263P4

DongHoon Lee
Prodigy 25 points
Part Number: AM263P4
Other Parts Discussed in Thread: SN74LV1T34

Tool/software:

Hello, This is DongHoon.

I designed a custom board using the AM263P4 and set the SOP to UART boot mode to check if the ROM code operates correctly.

However, I am not seeing the 'C' character output via XMODEM on the UART0 channel. I can't see any signals on the UART0_TXD(A6).

I suspect the clock source may be the issue.

I did not design the board with a quartz crystal for XTAL_IN(T1) and XTAL_OUT(R1), leaving them floating, and instead applied a 25MHz clock oscillator to EXT_REFCLK0(P2).

Based on my understanding of "5.6 PLL Configuration" and "6.4.1.2.1 PLL Module" in the SPRUJ55B, there should be no issue supplying the clock through EXT_REFCLK0 instead of XTAL.

However, in the note of "5.6 PLL Configuration," it states that an XTAL clock source is required.

Could this be causing the issue?

  • +1
    TI__Genius 10504 points

    Hi DongHoon,

    Even though you are using a 25MHz clock oscillator, you still need to have it connected to the XTAL_IN pin on the AM263P4. See section 3.1 in the AM26x Hardware Design Guidelines document and let me know if you have any further questions.

    Applying a clock signal to EXT_REFCLK0 will not supply the main clock input to the AM263P4 SoC, but can be used as a clock input for the device module clocks only.

    Regards,

    Brennan

  • 0 in reply to Brennan Hartigan
    Prodigy 25 points

    Hi Brennan,

    Thank you for the prompt response, which has helped me gain clarity.

    I am considering applying a CMOS oscillator.

    Similar to the AM263P4 ControlCARD using VDDS18_LDO as the power source for the Clock Buffer(SN74LV1T34), I am planning to use VDDS18_LDO as the power source for the CMOS oscillator. The oscillator output will be connected to XTAL_IN (T1), and XTAL_OUT (R1) will be left floating.

    I intend to use the "ECS-2016MV-250-CN," which is expected to consume a maximum current of 3mA.

    In section "6.8.6 Power Management Unit (PMU)" in the SPRSP81C, I confirmed that the load current supplied by the "1.8V LDO" is a maximum of 60mA. However, I could not verify the maximum output current that the "1.8V LDO" can provide. so I am unsure if there could be any power issues.

    Could you confirm if applying the "ECS-2016MV-250-CN" would be acceptable?

    Thanks.

  • +1 in reply to DongHoon Lee
    TI__Genius 10504 points

    DongHoon,

    If your maximum current consumption from the CMOS oscillator is 3mA that is ok. ECS-2016MV-250-CN is acceptable.

    If you are concerned, you can always use an external 1.8V regulator.

    Regards,

    Brennan