Author Topic: CurrentRanger with LTC2400 (ADC 24 bit)  (Read 262 times)

alexsh1

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CurrentRanger with LTC2400 (ADC 24 bit)
« on: November 21, 2018, 12:58:58 PM »
Hi Felix,

Did you consider using a higher resolution ADC for the CR?
I am currently working on a MilliVolt Meter based on LTC2400, voltage reference LT1019.
The resolution of this ADC is enough to make 6.5 digit meter.


Regards
Alex

Felix

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Re: CurrentRanger with LTC2400 (ADC 24 bit)
« Reply #1 on: November 23, 2018, 11:21:48 AM »
Yes, sort of, but not quite 24bit, that much resolution does not buy you much, unless you have very special other components to reduce noise by 1 to 2 orders of magnitude.
One of my prototypes used an external SPI DAC but it was too:
- costly
- noisy
- slow
- lots of code, separate library

So in the end I decided to compromise with the SAMD21 DAC, which works just fine.

alexsh1

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Re: CurrentRanger with LTC2400 (ADC 24 bit)
« Reply #2 on: November 23, 2018, 02:08:19 PM »
Yeah, resolution is one thing and another thing is that as you rightly pointed out the analogue section must be supporting it. Otherwise, it will be super noisy. I suppose at the end of the day, it all comes to costs. Your time is a cost element too.

Felix

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Re: CurrentRanger with LTC2400 (ADC 24 bit)
« Reply #3 on: November 26, 2018, 10:18:39 AM »
In my experiments, having an external high resolution ADC, vs the benefits, there is no real advantage.
Once I decided to use the SAMD21, which has a pretty decent and usable 12bit ADC, there was no incentive to add another part and supporting circuitry to the BOM.
Plus, even a good 16bit ADC is pretty expensive.
People may not realize but any extra parts (even passives) add up not just a multiplier component cost, but also other complications, all the way from sourcing, to assembly - extra room in pick and place, to testing etc.