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What is the jelly bean DAC du jour?

Hello Folks,

Haven't used DACs in a while, did it with PWM all the time. Now I need to design something that requires lots of low noise DC levels to be set.

What is the common jelly-bean 8-bit multi-DAC with a serial bus these days?

The requirements would be the usual. Multi-sourced if possible, lots of channels, under 50c/channel or at least under $1/channel, 8 bits or more, serial bus with two or at the most three wires, speed can be in the low kHz range. A chip select would be nice but that could also be handled by gating logic.

I have seen some nice octal 8-bitters like the TLC5628 which unfortunately needs an extra load command line (but that would be ok). Don't know whether that one is a mainstream part and I want to avoid settling for a boutique part, which is why I am asking.

Then there'll be the challenge to bus the data to several dozen modules with the DACs on them but that's a whole 'nother matter. Got to wait until the guys tell me what the bus is going to be. Hopefully nothing that needs lots of arbitration.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg
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LTC1090. 2 wire I2C bus, 8 ch.

Reply to
sdeyoreo

Wow, those are $12-$25 each from Digikey.

Reply to
mrdarrett

Thanks. It is a bit on the pricey side, probably because it's 10-bit.

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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Hello Spehro,

Good point. I am even pondering the use of a uC, cramming numerous PWM in there. Some will have to be SW because there are only so many CCR and only one long timer, usually. That way I'd have a neat little UART at my disposal that could take care of the host communication.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

You might do better price-wise with a digital pot than a conventional DAC.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
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Reply to
Spehro Pefhany

Hi, Joerg,

Take a look at AD8801. Octal 8-bit, $3.83 at 100. Has the standard nonstandard ghastly serial command set, of course.

John

Reply to
John Larkin

Hello John,

Thanks. That is a nice chip and AD has so far never let me down in terms of obsoleting stuff out of the blue. The street price seems to be around $5 at 100 but that would be fine in this application.

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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

I don't know how it compares, but I was looking for a cheap DAC a while ago and settled on the former Burr Brown 7611:

formatting link

Was one of the cheaper ones in the Digikey catalog when I was looking.

Worked for me.

Reply to
xray

Will a fast delta-sigma modulator on a CPLD or small FPGA be able to match your requirements ? You can fairly easily roll your own, and get plenty of channels out of a single part. You'll have to see whether you can run it fast enough to get the noise level at an acceptable level, though, but it's easy to outperform a MCU solution.

To improve noise, you could even combine 2 output pins through resistors.

Reply to
Arlet

Thanks. However, that's only one per package so it'll be around $3/ch.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Hello Arlet,

Yes, that is certainly an alternative. FPGAs are quite expensive though, and often power-hungry.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Hello Spehro,

Currently I am looking at the MSP430. There is only one timer on most of these, with 2-3 CCRs. If it doesn't have to do anything else I could add more in assembler. The need to listen to some kind of bus for value changes throws that a curve though. Plus in this case I'd have to filter them LC because the wee corners of an RC need to be muffled. Has to be whisper quiet.

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

There are a fair number of micros around with multiple hardware PWMs, often aimed at motor control. Philips LPC 8051 series come to mind as a low-cost alternative, but there are many others including PICs and MSP430s.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

The MSP430F149 has 7 or 8 PWM outputs from one timer.

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Reply to nico@nctdevpuntnl (punt=.)
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Reply to
Nico Coesel

CPLD are cheap. You can use micro for computations and CPLD for outputs. For example: a cheap ARM (qty 1: $3 to $4) and XC9572XL (qty

1: $2 to $3) can give you either 4 channels of 8 bits or 3 channels of 10 bits. You can build cascaded chips of CPLDs as cost of less than $1 per channel. It could even meet your 50 cents per channel at higher volume.

Depends on the drive loads.

Reply to
linnix

Hello Nico,

That would work. I hadn't looked at their big flagships yet, mostly the F2xx family because they finally managed to design good BOR capabilities into those, plus internal oscillators with a decent accuracy.

Do you think the F149 will stick around for a while? One version of the

427 was designed for electricity meters so hopefully that one will have good longevity. 
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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

Hello Linnix,

That's another idea although I can get octal DACs for around $4-$5. That would be a better deal then. Long term DAC availability is another matter but that can also become a real problem with programmable logic where the fashion changes much faster.

The FPGA I saw where pretty much always hungry. But so am I :-)))

--
Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

But the basic functions never change. I can implement the same shift registers using PLA equations as well as VHDL. In fact, I almost always use the same serial (micro side) / parallel (i/o side) shift registers for CPLD. CPLD would get cheaper with higher volume. Below $1 for the XC9572XL might be possible. I would rather overstock on CPLD then custom DACs.

If you really need the low power (more expensive), cool runner II need

12uA @1.8V for standy You can run at very low frequency and the only power would be driving the op-amp integrators. I don't think custom DACs would be any better.

CPLDs are not.

Reply to
linnix

days?

As far as I know the F149 is among the biggest in both flash, ram and I/O and most 'small quantity sellers' like RS-components and Farnell seem to keep it in stock for next-day delivery even if you order 15 pieces at a once. So it seems popular enough to keep around for a while.

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Reply to nico@nctdevpuntnl (punt=.)
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Reply to
Nico Coesel

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