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Looking for a 20 Bit DAC for Industrial Control

Discussion in 'Electronic Design' started by Chris Smolinski, Feb 27, 2007.

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  1. I'm revising a circuit for a client, and am looking for a 20 bit D/A.
    The present circuit uses the TI PCM1702, which is recently gone to "not
    recommended for new design" status. The DAC is used to produce a control
    voltage for a PWM circuit. It seems that most, if not all, of the 20+
    bit DACs out there now are delta-sigma type. I've never used one of
    these in such a circuit, they all seem to be for digital audio. I'm not
    concerned about any DC errors, as the DAC is in a feedback loop and they
    will be taken care of. I am concerned about noise in the DAC output
    causing jitter in the PWM signal, though appropriate filtering should
    take care of that. The DAC output only needs to update at about a 1kHz
    rate.

    That brings up the other problem - do these audio DACs need to be
    updated at a 44.1 kHz rate? Or can they just be updated at an arbitrary
    rate? Also, how critical is the clock used to drive the modulator? I'm
    not likely to have the necessary clock on the board already, although I
    could add it if necessary (I like to keep the number of clocks to an
    absolute minimum).

    Thanks for any insights.
     
  2. MK

    MK Guest

    Hello Chris,

    I have used DAC1220 (Burr Brown from TI) (a pair simulating a load cell in a
    functional tester). No huge issues. They are sigma delta but not audio -
    they quote settling time as 2mS so your 1kHz may be a little high.

    Michael Kellett

    www.mkesc.co.uk
     

  3. Hi Michael,

    Thanks for the info.

    I see they quote a settling time of 10 msec for 20 bit mode, and 2 msec
    for 16 bit mode. Have you found it to really be 2 msec for 20 bit mode?
    I see the settling time is for large signal changes, most likely I will
    be making small changes in normal operation.
     
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