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Old 4th May 2011, 07:52 PM   #11
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Very intriguing IC, more expensive, but looks to be worth the difference.

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Originally Posted by agdr View Post
A few things to look out for vs. the LM317:
* There is a minimum output cap requirement of 2.2uF for stability since it is an LDO.
I wonder if/how larger Cout values positively affect the performance? Looks like I'll be rooting through the site for references tonight...

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Originally Posted by agdr View Post
* Has a minimum load requirement of 0.5mA, so you would want to throw something like an 20k resistor on the output.
I was planning on a LED power indicator for each voltage, so that should suffice (as long as the LED doesn't somehow prevent the load from being sensed at power up)

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Originally Posted by agdr View Post
* 1.1A vs 1.5A for the LM317, but can be paralleled
I only need 500 mA, so this should work just fine.

Looks like I have to add a few on my next parts order
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Old 4th May 2011, 08:21 PM   #12
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The LT3080 is definitely more pricey! You could get a whole handful of LM317s for the cost of two 3080s.

If the amp you are powering has the typical 0.1uF (ceramic or film, HF bypass) + 10-20uF electro caps (reservoir) on the various chips rail-to-rail or rail-to-ground, you may already be over that 2.2uF on the output. If it were me I would go ahead and add the 2.2uF anyway, just to be sure, since it would be in parallel with the load bypass caps.

The LED-for-load is a great idea.
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Old 4th May 2011, 08:28 PM   #13
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Quote:
A few things to look out for vs. the LM317:
* Has a minimum load requirement of 0.5mA, so you would want to throw something like an 20k resistor on the output.
Just a polite FYI... the LM317 has a minimum load of 5mA, which I always assumed was why the datasheets use a 240 ohm resistor from output to adjust. Of course if your load is always pulling current of >5mA (a la the LED idea) it's of little consequence.
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Old 4th May 2011, 08:47 PM   #14
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Quote:
Originally Posted by agdr View Post
The LED-for-load is a great idea.
It was inspired by your avatar
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Old 4th May 2011, 11:16 PM   #15
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lol!

sofaspud: That is a good point about the LM317 - I had missed that - another 5x - 10X improvement over the LM317. 0.5mA - 1mA for the LT3080 vs. 5mA for the LM317.

Last edited by agdr; 4th May 2011 at 11:23 PM.
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Old 5th May 2011, 01:43 AM   #16
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I'm not totally sold on the LT3080 for this application. I'm not very familiar with the part though. I generally only use LDOs where the circuit demands it (or perhaps more truthfully, when I'm opposed to changing the ps enough to not demand it). I'd give it's use a twice-over, not a once-over, to ensure there are no thermal issues at 500mA.
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Old 5th May 2011, 03:15 AM   #17
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the LT3080 certainly looks interesting, seems it has very low noise (wish I had an apples with apples comparison of the noise specs between the LM317 and this)!

Ripple rejection doesn't appear to be quite as good as the LM317 but if the noise is indeed lower it would probably not be an issue. The datasheet claims the chip doesn't need a heatsink, so 500ma (1/2 rated capacity) shouldn't be an issue you would think....

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Old 5th May 2011, 03:38 AM   #18
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Default LM317 experiments and measurements

They say it doesn't need a heatsink, but they also tout the ability to parallel chips for increased current and "heat spread". At ~$4.50 a pop, that gets ridiculous real quick. From what I gathered, the Pd is <2W. Compared to the 20W claimed for the LM317. Maybe I just got the SMT versions' power spec.
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Old 5th May 2011, 02:31 PM   #19
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They imply that by saying that it can be used in "many applications requiring high current, adjustability to zero and no heat sink". They also tout the 350 mV drop, but that's in a configuration that uses a reference voltage, otherwise it's 1.35 V. I don't plan on using the reference voltage config, so that increased power dissipation is certainly going to generate additional heat.

Also, at the price, I think it's prudent to use heat sinks anyway. It can't hurt, it might help, and it looks cooler.
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Old 5th May 2011, 07:54 PM   #20
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Good point about the power dissipation specs - or lack of them! From this article the 1W - 2W appears to be the surface mount version, with the TO-220 package providing "higher power dissipation", but I have yet to find a spec for it in any of the LT literature. That is a little spooky.

Linear PR: LT3080 - Surface Mount 1.1A LDO is Easily Paralleled for High I(OUT) without Hot Spots

Given that, maybe the good old LM317 is the safest way to go, especially if you have a couple in the parts box right now.
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