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LM15851: initialization sequence

vic zap
Intellectual 740 points

Part Number: LM15851

Hi!

I have some questions regarding LM15851 initialization.

1. Does SPI_RES (POR register) supersede SWRST (CFGA register). I.e. SPI_RES resets the whole chip (including internal state machines, etc.), and SWRST resets register's content only. Is it correct?

2. Should I give the chip some time after issuing the SPI_RES command to get the chip reset before I could issue another command or could the next command be issued immediately after the reset?

3. In JESD204 Startup Sequence (8.3.1, p. 75), when programming JESD_EN = 0, then CAL_SFT = 1, and then JESD_EN = 1, should some delays be inserted between these commands to give them time to be executed, or could the commands be issued side by side without any delay?

Please, describe the initialization process in some more details then it described in the datasheet.

Best regards,
Victor.

  • 0
    TI__Guru* 91947 points

    Victor,

    SPI_RES resets digital logic like state machines and SSRST resets only registers. The registers are reset automatically during power up so you should need to issue the SWRST.

    You can issue other commands immediately after sending the SPI_RES command.

    I am looking into the last question.

    Regards,

    Jim

  • 0 in reply to jim s
    TI__Guru* 91947 points

    Victor,

    No delay is required because the ADC clock (DEVCLK) is so much faster than the SPI clock.

     

    The maximum SPI clock frequency is 24MHz, and it takes 24 SPI clock cycles for each transaction. So each transaction takes at least 1us.

     

    The minimum ADC clock frequency is 1GHz (1ns), so there are at least 1000 ADC clock cycles per SPI transaction.

     

    It takes about 320 ADC clocks to process “CAL_SFT=1” before the part would be ready for “JESD_EN=1”.

     

    So even if the SPI is running at the maximum rate, and the ADC is running at the minimum rate, the ADC still gets plenty of time to process the “CAL_SFT=1” event before the “JESD_EN=1” event occurs.

    Regards,

    Jim

  • 0 in reply to jim s
    Intellectual 740 points

    Jim,

    thanks a lot for the replies.

    I just want to get a little clarification. Does SPI_RES reset registers as well?

    Regards,

    Victor.

  • 0 in reply to vic zap
    TI__Guru* 91947 points

    Victor,

    I worded my earlier response incorrectly. This should have said "The registers are reset automatically during power up so you should not need to issue the SWRST".

    SPI_RES does not reset the registers.

    Regards,

    Jim

  • 0 in reply to jim s
    Intellectual 740 points

    Thanks a lot, Jim, for the fast replies.

    Now it's all clear to me.

    Best regards,
    Victor