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I'm using TI's REF200 as a 200uA current source but need something cheaper with similar precision (temperature stability, accuracy, etc). I'm using this in conjunction with an INA337 Inst. Amplifier, giving me great accuracy but too expensive.

This is to read an RTD so the current must be low to prevent self-heating but accurate enough to calculate 0.1 Degree C variations.

cdsiado
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  • This forum does not work well with shopping advice. If you are trying to find another way to accomplish a technical task that is one thing, but just wanting a cheaper part is not a functional solution. We have no details for what variation from spec are acceptable, we could write a new question for every single part in existence and write another set for every single situation for layouts, and then we could ask again in 6 months when prices change. – Kortuk Nov 08 '11 at 02:19
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    I learned a lot from the short time spent looking at that requirement. I now have a substantially better idea of what is available in that area for what $ and what the tradeoffs are. Such knowledge is probably best kept from the masses. Quite what the problem is in 'cluttering up the site' with specialistish answers if they are well tagged and indexed I know not, but it's increasingly obvious that I march to the beat of a different drum than is largely heard here :-). The subset of useful knowledge that is desired seems "a bit of a shame" . Whatever. – Russell McMahon Nov 08 '11 at 02:48

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A link to a data sheet and some idea of your key target parameters is always useful when asking questions such as this. It saves N people looking up the same data and ensures we are looking at what you really want to replace and not something only similar.
REF200 datasheet

I tried searching Digikey for "current source" and ordering results by price.

This seems much cheaper than the TI part and at 1st glance has similar spec - plus its MUCH more flexible I think.
If this is no good then working up Dikgikey offerings in ascending price order or specing tightly and sorting by price shoud produce something suitable.

NXP pssi12021.

$us0.66/1. $us0.26/1000
15 uA TO 50 mA programmable 0.5%
0.15%/K <- much worse than yours :-( Vsupply <= 75V !!!

ADDED

The 0.25% spec seems to leave only the REF200 and this IC from Digikey.
The PSIxxx has a far worse temperature spec (0.15%/K = 1500 ppm compared to 10 ppm for REF 200.

Temperature change of 1K is about 0.3% absolute so temperature stability is about 50% of temperature reading per K. Sounds wrong. The ratio of 1500ppm/10ppm = 150 :1./ The PSixxx is specified over a -55C to +150C range (!!!) so it's is just possible [tm] albeit unlikely that 0.15% is change over whole range. Unlikely! :-).

Roll your own should be cheaper than TI and as good or better, but more work.
How many do you need, what do you want to pay, what will you pay me ? :-)

Russell McMahon
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    Thank you Russell. I'm sorry my question did not fit the forum's rules. I figured I'd ask what I needed rather than ask several general questions to get to the same point. Point Taken. Love this forum and hope I can contribute my own 2 cents. – cdsiado Nov 08 '11 at 19:37