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LMK04808: Problems occur at low temperatures

Charles Jeon
Expert 2975 points

Part Number: LMK04808
Other Parts Discussed in Thread: TPS7A7300

Hi team

My client configured the system with the following blocks.

LMK04808 does not work properly when testing -5 ° operation to chamber.

Normally, PLL2 should operate in cascade after PLL1 of LMK04808 operates.

The problem is that PLL1 operates normally at low temperature, but PLL2 does not work.

Please confirm that there is no problem using LMK04808 as above.

  • 0
    TI__Mastermind 28590 points
    Hello Charles,

    I confirmed the dropout voltage of TPS7A7300 is acceptable for 3.8 V to 3.3 V. I didn't check the entire chain, but don't think that is likely your issue. Have you noticed any supply abnormality at the LMK04808 at room or cold condition? If necessary I could check more into the power path but don't think it is the problem unless there is some reason for concern.

    Can you elaborate more on what you mean by PLL2 not working? Here are some items that will help me better understand your issue:
    - Is PLL2 digital lock detect low?
    - Is PLL2 on or off frequency? Meaning are any clocks active and on off frequency?
    - What is the voltage at CPout2 at room temperature? At -5 deg C?
    - Finally, excellent for debugging PLL issues. If you configure the Status_LD for PLL2 R/2 output (LD_MUX = 0x12) and Status_Holdover = PLL2 N/2 output (HOLDOVER_MUX = 0x0E). Do you see both clock phases? What are there frequencies? In a locked condition, they will be stable and phase locked with respect to each other. Be sure to set LD_TYPE & HOLDOVER_TYPE to an appropriate output setting like output push-pull (0x03).

    One more item, can you confirm the programming procedure on page 48, 8.5.2 Recommended Programming Sequence is being used. Basically to do a software reset and then write all registers from R0 to R31?

    73,
    Timothy