From: "Bill sloman"
Subject: Re: LTC1298 voltage reference question
Date: Wed, 25 Sep 2002 00:34:57 +0200
Organization: Planet Internet
NNTP-Posting-Date: 24 Sep 2002 22:34:57 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Tom Faloon" wrote in message
> Ripple + Noise.
> The output should be fairly quiet. The 7805 will reject any ripple on the
> V supply by more than 60dB, and add very little noise of it's own.
Most three-terminal regulators are pretty noisy, particularly when compared
with voltage references.
The data sheets generally give typical noise levels.
The main problem is the band-gap reference - if you've got a 12V supply you
can use a 5V output voltage reference based on a buried zener reference,
which can be much quieter.
> If there is a lot of high frequency noise on the 12V supply, you could fit
> an RC filter at the regulator input. Anyway, I don't think this will be a
RLC filters are even better, but you have to make sure that there is at
least enough R to critically damp the resonance of the L and the C. I have
used the ESR of an electrolytic capacitor for the damping resistance, but it
isn't that well defined, and you run the risk that some "value engineer"
will replace you nice lossy tantalum chip with a big ceramic that isn't
nearly lossy enough.
Bill Sloman, Nijmegen