I thought I found an ideal micro power OpAmp for another low power LDO
I'm building in the LMV641. Small offset, RR output, 10MHz GBW, 2.6
V/us and still pretty good drive capability +/- 20mA.

http://www.national.com/ds/LM/LMV641.pdf

There's one thing I'm concerned about it specs a max differential
input of +/- 0.3V. Under normal operation this shouldn't be a problem
but at start up and shutdown this may be exceeded. Is this likely to
hurt the reliability of OpAmp?  Should I place current limiting
resistors on both opamp's inputs?

Schematic

http://i38.tinypic.com/108643d.png

On Tue, 14 Oct 2008 13:58:52 -0400, Hammy <s...@hotmail.com> wrote:

>I thought I found an ideal micro power OpAmp for another low power LDO
>I'm building in the LMV641. Small offset, RR output, 10MHz GBW, 2.6
>V/us and still pretty good drive capability +/- 20mA.
>
>http://www.national.com/ds/LM/LMV641.pdf
>
>There's one thing I'm concerned about it specs a max differential
>input of +/- 0.3V. Under normal operation this shouldn't be a problem
>but at start up and shutdown this may be exceeded. Is this likely to
>hurt the reliability of OpAmp?  Should I place current limiting
>resistors on both opamp's inputs?
>
>Schematic
>
>http://i38.tinypic.com/108643d.png


Many opamps have clamp diodes between their inputs. A few mA of
transient current won't do any harm. Your circuit looks OK as-is.

Incidentally, your circuit is backwards. Convention is input on the
left, output on the right. 


John

On Tue, 14 Oct 2008 12:32:33 -0700, John Larkin
<j...@highNOTlandTHIStechnologyPART.com> wrote:


>Many opamps have clamp diodes between their inputs. A few mA of
>transient current won't do any harm. Your circuit looks OK as-is.

Thanks John.

This is the first LDO I've built that actual performs identically to
the spice simulation.

>Incidentally, your circuit is backwards. Convention is input on the
>left, output on the right. 

Guilty as charged. I don't know why I do that sometimes. If you look
in the bottom right corner you'll see I stuck with convention for my
1/Beta schematic. Input to the left.;)
>
>John