Is anyone familiar with Maxim's MAX5318 18-bit DAC please? I hardly ever se e it used but it's significantly cheaper than competing chips from Texas In struments or Analog Devices.
Judging from its datasheet alone it's not quite as good; but, it seems to m e, not by enough to account for the price difference. I'm wondering if ther e's some other issue with the MAX5318 which I should be wary of. I'd especi ally like to hear from anyone who's applied its digital gain and offset: di d they cause any linearity problems?
(Please save the "Never buy Maxim" meme for some other thread. Here I'm int erested only in technical details. Thanks.)
see it used but it's significantly cheaper than competing chips from Texas Instruments or Analog Devices.
me, not by enough to account for the price difference. I'm wondering if th ere's some other issue with the MAX5318 which I should be wary of. I'd espe cially like to hear from anyone who's applied its digital gain and offset: did they cause any linearity problems?
nterested only in technical details. Thanks.)
The AD5780 has significantly better noise spectral density (8 vs 24 nv/root hz) and differential nonlinearity error (1 vs 2 lsb) than the MAX5318 but is similar in other respects.
Thanks, yes the AD5780's a nice chip all right. I've looked hard at it but this application's a bit too cost-sensitive. I have another in mind for the future which will need that extra performance - perhaps then.
Not really relevant to this thread TBH John but thanks for your interest. E ighteen bits is a sweet spot: the controlled element can't resolve to 20 bi ts so the extra resolution would be wasted anyway. It's for precise control of a DC signal, with a very long interval between updates. Main considerat ions are linearity, stability, temperature drift and, unfortunately, cost. The MAX5318 appears to be the best all-around candidate; I just didn't want to choose it then find that the reason it's cheaper yet not widely used is some awful technical shortcoming known to everyone but me :-D
Spooky - we may be on parallel tracks :-) I'd left space on the board for a higher-resolution ADC in case the results justify reading the DAC, to dis cipline it as you suggest. I'm confident though that an R-2R on its own, li ke the ones discussed so far, is the right starting point. After all, for p recision work at DC the likes of TI and AD suggest only those, strings or M DACs. I'd use an MDAC here, just as I'd use a better-quality R-2R - the lin earity of an 18-bit string DAC isn't good enough - but cost is the issue.
r a higher-resolution ADC in case the results justify reading the DAC, to d iscipline it as you suggest. I'm confident though that an R-2R on its own, like the ones discussed so far, is the right starting point. After all, for precision work at DC the likes of TI and AD suggest only those, strings or MDACs. I'd use an MDAC here, just as I'd use a better-quality R-2R - the l inearity of an 18-bit string DAC isn't good enough - but cost is the issue.
It seems like you are paying for a fast settling time (usec) when you don't need it. As John suggests, you could servo control a cheap DAC to get the resolution and linearity you need.
't need it. As John suggests, you could servo control a cheap DAC to get th e resolution and linearity you need.
In true newsgroup fashion, this thread hasn't seen an answer to its topic a nd is instead being dragged further and further away, by posts based on une ducated guesses about the OP's needs and goals. So this is it from me.
Sure I'm getting a faster settling time than I need - so what? Settling tim e's your consideration not mine; it's nothing I've decided to pay for. I'm also getting a better noise figure than I need - and I'm no more interested in that than in settling time. They come with the package, that's all, lik e an unnecessary paint job on a decent car.
Good luck with servoing a cheap - or, for that matter, expensive - DAC to g et better resolution, no matter how tight the resolution of the ADC you mon itor it with. If your hi-res ADC tells you your 18-bit DAC needs adjusting, you get to adjust it by one LSB out of 18 bits and no better. Anything els e is a Cloud Cuckoo Land attempt to create DAC bits out of thin air. What y ou gain from servoing is the ability to measure what the DAC's really doing and correct it. You need a better ADC so your measurements aren't meaningl ess, not because it can magically impart its higher resolution to the DAC.
What that costs you is expense and complexity (both of which may be worth p aying) and, in this application, one or two other performance factors which are more important and which I've said before I'm not going into. If makin g a poor, cheap DAC adequately mimic an expensive precision one were as sim ple in every application as adding a cheap ADC, the combination would long ago have killed the market for standalone precision DACs. For some reason A D, TI, Maxim and others still think they have a point and sell millions of them to suckers like me. But hey, warn them that you know better; maybe the y'll pay you a fortune not to blow the lid on their nice little earner.
onsdag den 4. november 2020 kl. 21.36.06 UTC+1 skrev jla...@highlandsniptec hnology.com:
don't need it. As John suggests, you could servo control a cheap DAC to get the resolution and linearity you need.
c and is instead being dragged further and further away, by posts based on uneducated guesses about the OP's needs and goals. So this is it from me.
time's your consideration not mine; it's nothing I've decided to pay for. I 'm also getting a better noise figure than I need - and I'm no more interes ted in that than in settling time. They come with the package, that's all, like an unnecessary paint job on a decent car.
o get better resolution, no matter how tight the resolution of the ADC you monitor it with. If your hi-res ADC tells you your 18-bit DAC needs adjusti ng, you get to adjust it by one LSB out of 18 bits and no better. Anything else is a Cloud Cuckoo Land attempt to create DAC bits out of thin air. Wha t you gain from servoing is the ability to measure what the DAC's really do ing and correct it. You need a better ADC so your measurements aren't meani ngless, not because it can magically impart its higher resolution to the DA C.
and they usually work by delta-sigma modulating only a few discrete levels
on't need it. As John suggests, you could servo control a cheap DAC to get the resolution and linearity you need.
and is instead being dragged further and further away, by posts based on u neducated guesses about the OP's needs and goals. So this is it from me.
ime's your consideration not mine; it's nothing I've decided to pay for. I' m also getting a better noise figure than I need - and I'm no more interest ed in that than in settling time. They come with the package, that's all, l ike an unnecessary paint job on a decent car.
get better resolution, no matter how tight the resolution of the ADC you m onitor it with. If your hi-res ADC tells you your 18-bit DAC needs adjustin g, you get to adjust it by one LSB out of 18 bits and no better. Anything e lse is a Cloud Cuckoo Land attempt to create DAC bits out of thin air. What you gain from servoing is the ability to measure what the DAC's really doi ng and correct it. You need a better ADC so your measurements aren't meanin gless, not because it can magically impart its higher resolution to the DAC .
paying) and, in this application, one or two other performance factors whi ch are more important and which I've said before I'm not going into. If mak ing a poor, cheap DAC adequately mimic an expensive precision one were as s imple in every application as adding a cheap ADC, the combination would lon g ago have killed the market for standalone precision DACs. For some reason AD, TI, Maxim and others still think they have a point and sell millions o f them to suckers like me. But hey, warn them that you know better; maybe t hey'll pay you a fortune not to blow the lid on their nice little earner.
I am sorry for having wasted my time answering a question for such an ungra teful asshole such as yourself - it WON'T happen again!
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