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DAC38RF82: 81180 9G mode cannot output

Kailyn Chen
Genius 9560 points
Part Number: DAC38RF82

Hello,

 Our customer used DAC38RF82  for his application, when  configuring DAC38RF82 81180 mode, 8G sample rate can be output, but 9G cannot output. 

DAC38RF82 81180 9G mode does not output. Using internal PLL, input clock 281.25MHz, N=1, M=8, VCO=9000MHz

DAC38RF82 81180 8G mode but normal output, internal PLL, input clock 250MHz, N=1, M=8, VCO=8000MHz

And he did some test:

 He  found that the DAC internal phase-locked ring did have a problem with 9G sample rate and then confirm that the reference clock of the external input is stable and the error is reasonable. Since 8G sample rate can be played properly, the input power should be fine.

The related several registers are configured as follows:

0x31: 0x0400

0x32: 0x0708

0x33: 0x8A14

 Because the 8G sample rate plays well, a lock exception occurs when the DAC clock is changed to the 9G sample rate for this input only.

He also read  the JESD_ALM registers （addrss：0x64~0x6B），he read 0xA, does it affect the DAC output? 

PS：JESD Alarms for Lane 0~7 Register[3:0] ，ALM_FIFO0_FLAGS Field。

Best regards

kailyn

  • 0
    TI__Genius 9560 points

    HI,

    During test,  if modified the parameters of the PLL_VCO word and could obtain a correct 9G output.

    To gain a deeper understanding of this issue, could you please provide me with more detailed information about the PLL_VCO word if possible?

    Best regards

    kailyn

  • 0 in reply to Kailyn Chen
    TI__Mastermind 22030 points

    Kailyn,

    The PLL_VCO field is used to tune the VCO. When the on-chip PLL is used, then this will need to be swept while reading back the value of PLL_LFVOLT. When PLL_LFVOLT reads back between 3 and 5, then the PLL is locked.

    See an example of this in python below:

    for i in range(128): # start index is 0, ending index is 127

    dac.write(0x06, i)

    pll_lf_volt_readback = dac.read(0x06) & 0x00E0 # only look at bits 7:5

    if 3 <= pll_lf_volt_readback <= 5:

    print('PLL is locked')

    break

    Regards, Chase