The LTC datasheet "crows" about low current in dropout. Yeah, it's worth
crowing about since not all chip use what is called a "sat catcher"
circuit. High current in dropout with PNP pass devices can be a problem.
I've seen Micrel regulators that are horrible in dropout. The sat
catcher is yet another feedback loop, so it is best to stay out of low
dropout if possible.
Generally when I buy a LDO, I use the type with a P-fet rather than PNP.
I'm not sure if any of these exist with low noise. [I'm usually more
concerned with stability.] TI makes good ones. The P-fet pass device
doesn't need a sat catcher, so there is one less loop to worry about.
Having designed both types, I find the P-fet pass much easier to
stabilize. Bipolar devices don't isolated as well as MOS.
I'm not familiar with rubycon caps. The low ESR large value caps are
"organic semiconductor." OSCON is a common brand from Sanyo. Finding the
ultimate cap is nearly as much fun as finding the ultimate LDO. Check
out Nichicon. Or you can stick with the Rubycon. Glancing at their
website, they seem to copy the Nichicon product line.
On 11/24/2011 1:37 PM, Tim wrote:
Hi All
,
I find it interesting that this subject came up just as I was looking
into cleaning up some of my supplies that power my RB's.
Anyway....
I just bought two of these to play with
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=130605436528
and they're based on this device...
http://www.linear.com/product/LT1764
regards
Tim
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