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DAC3482 lost clock

Michael Koelbl
Intellectual 290 points

Hi,

I've the problem that we see alarm_dataclk_gone (Bit 9) and alarm_dacclk_gone (Bit 10 in config5) among other alarms but I think as long as the DAC sees/accepts no clocks the other alarms are aftereffects.

I'm sure that both dacclk and dataclk are applied: dacclk is ac-coupled and both lines have the common-mode voltage of 0.2 V which indicates that the dac internally bias the two lines, levels are OK. For dataclk I can measure the 110 Ohm dac internal termination, level is OK and as written later the dac responds to the application of dataclk as then dacclk alarm comes.

First I had both dacclk and dataclk always running and I got both clock-lost alarms. As there is mentioned in the data sheet that dataclk shall be applied later in the start-up sequence I gated the clock and now, as long as only dacclock is applied I get only dataclock loss alarm but as soon as I enable dataclock I get both alarms.

I have 5 boards (own design) and all are showing the same behavior.

Has anyone an idea?

dacclk frequency:13.75 MHz

dataclk frequency: 55 MHz (at this time for better measuring, later 220 MHz)

We're using only FRAME signal, SYNC and OSTR are not connected.

  • 0
    TI__Guru* 78324 points

    Michael,

    You may check out the following document on the clock alarms.

    http://www.ti.com/lit/an/slaa585/slaa585.pdf

    Basically, the clock alarms are a set of counters. The counter located on the DATACLK side counts the number of DACCLK cycles and triggers alarm if the number of cycles is not within expectation. The same applies to the DACCLK side.

    You may want to check the accuracy of the two sets of clock to make sure they are the right ratio. Also, since DACCLK is slower than DATACLK, I am assuming on-chip PLL is used. Please double check your PLL setting and PLL lock status as well.

    The following forum may help as well.

    http://e2e.ti.com/support/data_converters/high_speed_data_converters/f/68/p/151038/548084.aspx#548084

    -Kang

  • 0 in reply to Kang Hsia
    Intellectual 290 points

    Hi,

    I solved the problem. Problem was an incorrect start-up procedure. I added toggling the reset pin and switched off DATACLK  during first part of startup and then it worked.

    Thank's,

    Michael