how to choose a precision ADC for a DIY power supply? - Page 1
Forum section: electronics / projects

author: exe
author_rank: Unknown
timestamp: February 17, 2020, 08:10:07 pm
content: Hello!I'm trying to find a ADC for my project (a lab power supply). The problem I have is that there are simply too many ADCs to choose from. I'm lost. May someone could suggest a a good ADC or confirm my choice? So far I settled on ADS131A04 (TI) . I only considered TI parts, but I don't really care about the manufacturer, it just stars alligned this way, any other vendor is fine.To narrow-down a little bit, I defined the following requirements. They are somewhat arbitrary, but I had to provide at least some specifications, otherwise I'd need to choose from too many parts.resolution: 16bit or more because why not. I want to have 20000 count measurements, though not sure if I have skills for that (noise, offset, drift, etc problems)architecture: sigma-delta because presumably it gives better linearity comparing to SAR, but I'm noob herenumber of channels: 4+ differential channelsinterface: SPI because it's simple and robustextra features: external reference, I want to attach MAX6226 in ceramic package, this should presumably improve long-term drift.*price: preferably below $10, but since it's a one-off build I'm fine going a bit above if needed, but I'd like to avoid too-advanced parts that are hard to use (i.e. too many settings).package: everything but BGAinput impedance: presumably doesn't matter, I'll have an input bufferfreshness: among many available designs, I picked the freshest one. There are 10-20y.o. parts from Burr-Brown, etc, may be they are as good as modern or better, but I hoped that modern parts should be superior or at least better spec'd. Obviously I cannot prove that, if I had so much experience with ADCs I wouldn't ask this question.* I know that friends don't let friends buy Maxim parts, but I don't see any other 2.5V refs in hermetic packages on Mouser for a reasonable price.EDIT: typos

author: David Hess
author_rank: Super Contributor
timestamp: February 18, 2020, 05:29:28 am
content: Quote from: exe on February 17, 2020, 08:10:07 pmPick a resolution commensurate with your linearity requirement and pick a linearity requirement commensurate with your display counts. This means treat a 16 bit converter with only 14 bits of linearity as a 14 bit converter. But see immediately below.QuoteEither would be appropriate but an SAR will require extra processing to remove excess noise. Delta-sigma will be a better choice if lower sample rates are acceptable which is likely the case for a visual readout. Performance above 16-bits will require careful attention to noise and drift outside of the ADC.QuoteIt is often the case that more modern analog parts are not any better than older ones going back a couple decades. I would be more interested in availability and packaging.

author: exe
author_rank: Unknown
timestamp: February 18, 2020, 12:15:10 pm
content: Thank you very much, I think I'll stick with my pick as it looks to be reasonable. I'd say it well the specs well exceed my needs, but it's good to have some headroom. I also don't fully trust datasheets, I think they are often written to give a better impression of the parts than they really are.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 18, 2020, 04:14:19 pm
content: The choice looks Ok, though I don't know why one would need 4 channels and simultaneous sampling. Chances are this converter is originally made for something like power metering. This group of ADC is OK: better DC performance and gain stability than the audio converters and often cheap.What else except voltage and current would one want to measure ?For a multiple channel supply the channels are usually isolated and thus separate ADCs.

author: exe
author_rank: Unknown
timestamp: February 18, 2020, 04:37:18 pm
content: What I plan to measure. Besides current and voltage, I wanted to measure temperature, and I might have a separate current shunt for current sink. If I manage to use the same shunt for bidirectional current sensing, then I can live with a two-channel ADC (temperature can be measured by the ADC in MCU as precision is not needed, but this means writing more code, so I'd prefer not to do that).I want to build a two- or four-channel power supply, each channel is a separate and isolated board.

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 18, 2020, 04:40:46 pm
content: For a PS application, I used this one: LTC2460https://www.analog.com/en/products/ltc2460.html#product-overviewTicked all my boxes and fair pricing.