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Original question:

LMX2594EVM: Problems with Digital Interface / Set a Frequency

LMX2594EVM: Programming Digital Interface (SPI) failes

Marcus Meierbeck
Prodigy 100 points
Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

Hi,

the last problem i mentioned in my "LMX2594EVM: Problems with Digital Interface / Set a Frequency" thread is still existing. please read for details.

problem: i want to control the LMX2594 with my raspberry pi 3 b+ over the SPI interface. This actually works fine, when the raspberry pi works as controller and as power supply for the LMX2594EVM at the same time. Since i can't use the raspberry pi as power supply, because the integrated 3,3V voltage controller will not provide enough current in some cases, i had and still have problems - seemingly with the communication - when i change the power supply. In this case i conncect a power supply at the Vcc SMA connector. For SPI communication the raspberry pi is connected to CSB_TP, SDI_TP, SCK_TP and GND_TP.

what i do: my controller runs "Recommended Initial Power-Up Sequence" (datasheet 7.5.1) OR Recommended Sequence for Changing Frequencies (datasheet 7.5.2)

error: for some attempts (about 3/10) the requested frequency is not visible with the spectrum analyser conntected to RFOUTAP (e.g. 3 times wrong frequencies, 7 times correct frequencies). A readback with Ticspro shows that some register have wrong values. There is no correlation between requested frequencies and errors.

While using the raspberry as controller and power supply at the same time i have zero errors running the sequences for about 2000 executions.

Do you have any ideas where there could be a problem or possibilties for solving? Thank you very much.

Regards,

Marcus

  • 0
    TI__Mastermind 28001 points

    Marcus,

    Sounds very resourceful using Raspberry Pi to program our PLLs.

    If I get what you are saying, using Raspberry PI to program and as a power supply works, but it does not work with a separate power supply.   Perhaps this could be some kind of grounding issue.

    Also, realize this device has a power on reset.  So if you read back regsiters that look like they have not been programmed at all, then the registers are being reset.  You can see what the power on reset state of the registers is by toggling the RESET bit from 1 to 0 and then reading back the registers.

    Regards,
    Dean