SV: Re: [sdiy] 16bit DC, DAC, SPI!

[Eric Brombaugh]

Adam Schabtach wrote:

> I've been looking for essentially the same thing that Karl is looking for.
> Another candidate is the LTC1655. Its specs say it is quite accurate and it
> has a serial interface. It also comes in DIP and SOIC packages which may be
> a little easier for DIY than the MSOP package that the AD5663R comes in.
> (SMT is no problem for me in general, but those MSOP packages look teeny! I
> haven't tried to work with one yet.) Unfortunately they're not dirt cheap.
> They're around US$17 from Digi-Key.

What are the general criteria for these applications? I'm inferring the 
following:

* Large packages for easier DIY
* SPI interface
* resolution >= 16 bits
* Gain & offset accuracy > ?
* Small qty cost < $10
* Sample rate ?
* Conversion type != sigma-delta (charge transfer or resistor ladder?)
* Supply voltage (3.3V, 5V, +/-15V)?

I went through a similar search a while back and found that cheap SPI 
DACs in the 16-bit range are pretty scarce, mostly because none of the 
usual suspects stock them. The ones that are cheap+available have poor 
linearity that degrades their accuracy despite the high resolution.

The LTC1655 looks pretty nice. I've also got an application that uses 
the LTC26x4 quad SPI DAC. They're around $5-$10 (non-stock @ Digi-Key 
however) depending on resolution (12, 14, or 16). Small package, but the 
SPI clock rate is 50MHz so you can use them for fast sample rates. Plus 
the DNL is better than 0.2LSB on the 16-bit part!

Not sure how good LTC is with samples, but if you register with a 
company email you might get lucky. ADI and Microchip are famously 
generous with this (more companies should be - I'd guess it's a really 
effective way of getting good buzz).

Eric