Re: What is the jelly bean DAC du jour?

Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

Hello Spehro,


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.


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.


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


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.


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.

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

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
.

Relevant Pages

  • Re: What is the jelly bean DAC du jour?
    ... 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? ... 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. ...
    (sci.electronics.design)
  • Re: What is the jelly bean DAC du jour?
    ... 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? ...
    (sci.electronics.design)
  • Re: What is the jelly bean DAC du jour?
    ... 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? ...
    (sci.electronics.design)
  • Re: What is the jelly bean DAC du jour?
    ... 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? ...
    (sci.electronics.design)
  • Re: What is the jelly bean DAC du jour?
    ... Haven't used DACs in a while, did it with PWM all the time. ... 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? ...
    (sci.electronics.design)
Quantcast