[time-nuts] "Audio" DAC for GPSDO?

Bob Stewart bob at evoria.net
Mon Jun 2 19:22:45 EDT 2014


Hi Poul,

I've been reviewing microchips literature and the way I read it is that the DAC isn't sensitive to staying at a fixed value.  If it's on, the FIFO is fed to the DAC.  If the FIFO is drained, then the user-settable default value is fed to the DAC.  When the output amp is turned off, it goes to a high impedance output.  I also noticed that Finput can vary from 0-45 khz.  I'm not certain what a 61db SNR would mean at DC values.  I see that the specifications are for a 15 uA load.  I assume that's not hard to meet with a typical op-amp.

It's interesting that in one paragraph they call the DAC default register a safety feature for industrial control applications, and then a few inches later a black box warns that it's not recommended for control type applications.  


Bob



________________________________
 From: Poul-Henning Kamp <phk at phk.freebsd.dk>
To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Monday, June 2, 2014 4:08 PM
Subject: Re: [time-nuts] "Audio" DAC for GPSDO?
 

In message <1401742940.44103.YahooMailNeo at web142705.mail.bf1.yahoo.com>, Bob Stewart writ
es:

>Could someone explain to me how such an audio DAC differs from a non
>-audio DAC and why it's not suitable for this application?=A0 Is this just 

>a disclaimer from microchip to avoid liability or is there some practical
>reason to go with a traditional DAC?

A lot of them have DC protections, so you can't leave them at a particular
input value for very long before they go into safety mode and clamp the
output to zero.

Your speakers love them for this, your OCXO not so much.


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