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DAC38RF83: JESD Alarms and VCO range value

Daniel Malouin
Prodigy 20 points
Part Number: DAC38RF83

Tool/software:

Is it normal that I have to modify for each of the cards that we have with a DAC38RF83, a different VCO range value (page 4, register 0x33: PLL Configuration 2 register)? I use the value 0x5128 for one DAC (PLL_VCO = 0x51, PLL_CP_ADJ = 10) and for another 0x4A18 (PLL_VCO = 0x4A, PLL_CP_ADJ = 3). For this second DAC, reducing the VCO frequency range was not enough, I also had to reduce the charge pump current so as not to trigger JESD alarms. Is this variability normal or is it a not so good hardware design? I need to change these values ​​to set the PLL_LFVOLT field value (register 0x06) between 3 and 4 before starting the SYSREF generation as mentionned in the Startup sequence of the datasheet. Thank you!

  • 0
    TI__Guru 71429 points

    Hi Daniel,

    Yes, there will be variations amongst the DAC38RF83 devices. We recommend to change only the VCO code. You should not need to change the PLL charge pump setting

  • 0 in reply to Kang Hsia
    Prodigy 20 points

    Hi Kang,

    Let's say the temperature increases significantly during signal generation from the DAC and the VCO value no longer matches with the temperature range on the table, should I dynamically change the VCO value or is it just useful to do so during the startup sequence?