What is the jelly bean DAC du jour?

LTC1090. 2 wire I2C bus, 8 ch.

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

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

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.

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

Best regards, 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

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.

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:

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

Worked for me.

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.

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

Hello Arlet,

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

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.

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

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

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

Depends on the drive loads.

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

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 :-)))

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

CPLDs are not.

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.