Favorite Buck Regulators

Yup. In that kind of situation, you really want some significant margin on whatever circuit you use to allow for the Transzorbs etc. some room to do their clamping. There are a couple of chips that can take 80-100V input, and they would be easy to protect, but it's also possible to just add a regulator and use an external switch as in the off-line (and many telecom 48V input) switchers.

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Okay, what is it this time that's not "exactly in line with what the regulator was designed for" ?

This time, nothing. That time, I wanted to be able to adjust the regulator output from a DAC, and I wanted to verify that it didn't have any nasty transients.

:)

The 24V is coming from a switching regulator about two inches away from the board, in a quiet environment. So I would expect that it's pretty clean.

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Seems straightforward with something like

Mostly I'm thinking of how they allowed their LMX23xx line of PLL chips to be steamrolled by Analog Devices. There may be some other categories where NatSemi doesn't hold the #1 position in chip performance, but that's the one that came to mind first.

They do have some great RF ADCs but it's not easy to point at one ADC and say it's uniformly "better" than another. There are too many different parameters and too many different applications... and sometimes the most important attributes aren't mentioned on the data sheet.

-- john

Be happy that it only went "blurp". I had a LDO from them, client insisted on using it against my advice. Long story short it had an undocumented flaw. I gradually raised the source impedance during testing ... *KABLAM* ... a capacitor vaporized. Turns out it burst into oscillation when you got above a certain limit. The datasheet was completely silent about this.

And they haven't fixed it in roughly 10 years. We had an undocumented problem as well. Not exactly the same as yours, but caused us to eliminate the Simple Switcher as a contender. We never looked back.

Somebody quoted a saying, maybe in this group. It went something like this: When you are about to get hit by a steamroller you can either become part of the steamroller or become part of the road :-)

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That one is a voltage mode control which is always risky. I still find your story hard to believe. Now if you experienced it with the evaluation board, I'd say NS had a problem, but if not, it was most likely something you overlooked.

If you want low phase noise PLLs, you don't go to NS or AD. You go to Peregrine and Hittite.

Come on. You have your sampling frequency, RF or IF frequency and the available SFDR. That pretty much sorts it out. It's fun enough to team drivers of company A with ADCs from B. And if your sample clock generator is not good enough, you won't see the difference at all.

regards, Gerhard

Hittite's HBT parts are great in certain respects but they bring a different set of compromises, compared to the CMOS parts from AD and NS. They have historically needed much more power, for instance.

Either way, the availability of "better" chips from Hittite and Peregrine would move National down the leader board to #3 or #4 in the PLL performance category, knocking them out of the second-place slot beneath the ADF4xxx parts.

True enough for a lot of applications. Others, like phase comparators, are affected by some of the more obscure specs. Thermal stability is important, as are certain under-documented properties of the sample/hold front end. Even the effect of clock noise on jitter performance is one of those things that isn't quite as simple as the data sheets make it look.

-- john

That *was* a good datasheet. I wonder if the writers went off to work at LT?

Tim

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I am finishing a desing with LM2574 wich is a 40 V in, 3.3 V (LM2574-3.3) x 0.5 A out, SMD and DIP-8 packages are available. I have seen it in other commercial designs as well. Hope it helps!

Gentlemen. Could we please have some part numbers? They are printed on the bodies of the parts in question.

I dispise gossip, but dislike buggy parts a lot worse.

RL

Sorry I don't have a part number. As I said, that was 10 years ago. I just remember that it was a three-terminal plastic package similar to a to-220 and was called Simple Switcher.

It's been very long ago but IIRC mine was the LM2931. Another part where I have experienced unexpected pathologies not so long ago (in 2006) was the TPS71550, also related to input impedance issues. Considering that this thing is advertized for ultra low power that is a rather sad state of affairs.

Long story short I despise LDOs and advise clients not to use LDOs. Occasionally I am overruled but then at least I've told them :-)

"Leakage Null Control Circuit" ?? Bwahahahahahaha!

...Jim Thompson