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LMK04828: Start-up

Nicolas Oria
Prodigy 120 points
Part Number: LMK04828

HI

I am trying to bring to life the LMK04828 without success.

I have few questions:

1) Is the SPI operational even if the PLL are not locked/running? Even if neither the VCXO nor the CLKin for PLL1 is running?

I issued SPI write accesses but when trying to read the line is stuck to 0[V¨].

2) IS it mandatory to provide the CLKin to get the LMK started? I know I have to provide the CLKIN but for the moment I am just trying to get the device moving.

One stuff I measured is that my VCXO does not output any clock. I checked its config and it seems all good. Only the VC pins i.e. CP1 is at 0[V]. I do not get why it is like this

Thanks

Nicolas

  • 0
    TI__Mastermind 33770 points

    Hi Nicolas,

    SPI is operational even if the PLLs are not locked or running, and even if there is no clock input on CLKin pins or OSCin. There are a few things to consider with SPI transactions:

    • By default, LMK04828 starts in 3-wire SPI mode, so readback data will come out of the SDIO pin. See the datasheet description for Register R0 for more information.
    • There are three registers at the end of the addressable space (0x1FFD, 0x1FFE, 0x1FFF) which are used to lock the SPI bus. If the SPI bus is locked, no writes will take effect. See the datasheet section 9.7.9.10 for more information.

    Here is an example SPI transaction with the SPI bus unlocked in 3-wire mode:

    Is CPout1 at 0V when there is no CLKin signal? By default, POR should enable holdover and program the CPout1 voltage to about midrange (on my EVM I see 2.12V by default). This could suggest that the VCC pins are not adequately soldered, or that VCC is not being delivered to the supplies.

    Regards,