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PCM1754 Settling Time and Conversion Speed Numbers?

W
Prodigy 30 points
Other Parts Discussed in Thread: PCM1754

Looking for some concrete numbers regarding settling time and conversion speed for the PCM1754 audio DAC.  I have some system requirements constraints and need to be sure I'm meeting them.

Does TI have a number for the full scale settling time of this chip?  Since it's not in the datasheet, I am trying to derive it based on system clock specs, serial data setup and hold time, oversampling considerations, etc.  But it would be nice to have a real number from TI on this.  Based on 200 kHz max sample rate, one could say settling time is less than 5 usec, but it should be much faster than that.

  • 0
    TI__Guru**** 189401 points

    Hi,

    Unfortunately, we do not have data on this parameter.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 30 points

    Could I please get an estimate of settling time, or could TI help verify my general settling time estimation approach? 

    There is information in the datasheet that states "The PCM1754 automatically controls the oversampling rate of the delta-sigma D/A converters with the systemclock rate. The oversampling rate is set to 64× oversampling with every system clock and sampling frequency." (pg 16)

    And also, "The combined oversampling rate of the delta-sigma modulator and the interpolation filter is 64 Fs." (pg 28)

    If Fs is 192 kHz, can I interpret the above statements to mean that the D/A is over-sampling at 12.288 MHz, indicating a probable settling time of 81 ns or less?

  • 0 in reply to W
    TI__Mastermind 27980 points

    Hi W,

    The DAC in the PCM1754 is a Delta Sigma DAC and therefore the group delay/delay time will be the measurement that will tell you how long from a signal being input to the part until it will produce a valid output for the input. This is specified on page 4 of the PCM1754 the data sheet it specifies the delay time is 18/Fs. So if you are running at 192k sampling, the delay will be ~94 usec.

    Justin

  • 0 in reply to Justin Bohr
    Prodigy 30 points

    Justin Bohr said:

    Hi W,

    The DAC in the PCM1754 is a Delta Sigma DAC and therefore the group delay/delay time will be the measurement that will tell you how long from a signal being input to the part until it will produce a valid output for the input. This is specified on page 4 of the PCM1754 the data sheet it specifies the delay time is 18/Fs. So if you are running at 192k sampling, the delay will be ~94 usec.

    Justin

    Thank you for the response, but based on your numbers the PCM1754 cannot perform conversions faster than ~11 kHz.......  I doubt this is true since it is an audio DAC specified for almost 100 kHz input.

    You were looking at the delay time of the internal filter, which oversamples as much as 8x.  This means the delay time of the filter is actually (18/Fs) /8.  That works out to ~1.2 usec.  The settling time of the DAC should be even faster than this.  Can you verify or correct my earlier calculation based on datasheet info that resulted in an 81 ns settling time? 

  • 0 in reply to W
    TI__Mastermind 27980 points

    Hi W,

    We do not have an exact measurement of the DAC block settling time as it is more than sufficient for the Audio band which this part is designed, we can tell you the delay it takes to get from the input to the output of the interpolation block at 192 kHz which is 94 usec, and when at 192 KHz the oversampling is 2x not 8x as this block runs at 384 KHz. The DAC block and the modulator block are both running at 6.144 MHz.

    Justin