Best way to add external dacs

[rhdf]

And a year later..
I put this on hold for a while but are back on track now.

Looking at possible candidates for a 8 ch SPI dac I've found 2

TLV5630 from TI, in tsop20 or soic20 (nice for prototype)
http://www.mouser.se/Search/ProductDetail.aspx?qs=7KMwW2o1%252bmQiAwmvIPv%2fNg%3d%3d

and MAX5725BAUP+
http://www.mouser.se/Search/ProductDetail.aspx?qs=0JU57JYmZjtBqXkYujZL9A%3d%3d

the max-part is half the price, and I cant find any big differences (maybe I don't now what to look (out) for)

The TI dac is used by in the Midibox "Aout-NG" for more or less the same purpose as I plan to use it for
http://www.midibox.org/dokuwiki/aout_ng

[dmills]

IMHO go with the TI unless you are only building one unit....

The Maxim part you will be able to get a few of now, but you just try getting a few hundred in a year or so, there is a reason folks are reluctant to design their stuff in unless you are buying many wafers worth on 6 months lead.

I have been burned far too often by muppets designing in Maxim, yes, I know they have some unique and interesting parts, just say no!

I will make a partial exception for the jellybean RS-232/485 stuff providing there is a pin compatible second source.

It is a pity, but the business model seems to be to occasionally run a wafer of the obscure stuff to provide ready sample availability and then only run production quantities if someone places an order large enough to warrant it.

I suspect that anyone who has been around a few years has probably been bitten.

Regards, Dan.

[David Hess]

There is a big price premium going from 8 to 10 or 12 bits for multichannel DACs.  If 8 bits is enough, then separate DAC channels are the way to go.  Above 8 bits, multiplexers and track and holds with one DAC is competitive in price but not in layout space.

This gets tricky if simultaneous updating is absolutely required.  If that is required with a multiplexor and track and holds, then another switch and track and hold stage is required for each channel and offhand I do not know of any designs which went to that much effort.

Tektronix had good results with a 12 bit DAC, multiplexor, and 8 to 16 track and holds in their early designs but they did not require simultaneous updating.

[NorthGuy]

PIC16F1773 (or PIC16F1776) has 3 10-bit DACs and costs $2. You can use 2 of them to get 6 channels for $4.

Since they're MCUs it'll be very easy to communicate and synchronize. And they have plenty of pins for that. You can control them from your MCU, or you can remove your MCU and use PICs themselves for control.

You can run them at 3.3 or 5V (or anywhere in between). You can use DIP for prototyping/breadboarding, then switch to QFN for production.

[David Hess]

PIC16F1773 (or PIC16F1776) has 3 10-bit DACs and costs $2. You can use 2 of them to get 6 channels for $4.

These have 10 bits of resolution but they have more like 8 bits of guaranteed accuracy (2 LSB INL!) which is common for microcontroller and cheap DACs; check the specifications which do not even include drift with temperature.  For some applications this is tolerable but these parts really should be compared with good 8 bit DACs and not good 10 bit DACs.

[NorthGuy]

These have 10 bits of resolution but they have more like 8 bits of guaranteed accuracy (2 LSB INL!) which is common for microcontroller and cheap DACs; check the specifications which do not even include drift with temperature.  For some applications this is tolerable but these parts really should be compared with good 8 bit DACs and not good 10 bit DACs.

The only important thing is if the specs meet the OP's requirements or not.

[JPortici]

- Never use maxim parts unless you can't find any alternative. Reasons have been already said.
- I like spi. Try and see if you can find daisy-chainable DACs (that has an SDO output) so you can use a sigle CS pin, then DMA triggered by a pwm channel is your friend (the pwm channels generates the CS signal AND the DMA trigger)
- I also like PWM, if ripple/settling time (i would use this instead of rise time) is acceptable for the application. just use a bigger chip if you fear of running out of pins, those ARM like to come in big packages.
- I don't like I2C, i find it harder to automate

[dmills]

Concur, SPI is usually the way to go.

I2C is IMHO far more software pain then saving a few pins for slave selects usually justifies, it is easy to get it to 'work' but getting it to work with industrial grade reliability is IME a much tougher proposition, and it is painfully slow.

73 Dan.

[rhdf]

For what I'm building now  I might get away with using the maxim-part since its more or less a one-off

basicly its a small board with  MCU,  audio-codec and a DAC + the needed passives.
The purpouse is some kind of test-rig/prototype to wich i can hook up the analog stuff.

(since my synthproject never will  come near a production-line I can probably buy all the Dac:s in mousers stock and have supply for looong time )

[danadak]

See attached, 16 16 bit PWMs on one PSOC chip. Looking
at remaining resources probably could do another 8 16
bit PWMs.

And I did not do this but probably could add 4 8 bit analog DACs
with OpAmp buffered outputs.

There is also a wavedac component that can gen sine, tri, ramp, square
wave outputs. Not sure that may be limited to either 2 or 4 channels.


Regards, Dana.

[danadak]

I was able to add 4 Wave DACs and the Digital Filter 2 channel, IIR or FIR or BiQuads.....

See attached. Note you would use 2 of the WaveDacs as ordinary DACs for the filter
to drive 2 filtered channels back into time domain signals. Also you would use the
SAR or DelSig onboard to feed samples to the digital filter. And the DMA to automate
it.

One chip.


Regards, Dana.