Re: Current source design (tricky?)

From: Fred Bloggs (nospam_at_nospam.com)
Date: 03/12/05 

Date: Sat, 12 Mar 2005 12:25:46 GMT

Larry Brasfield wrote:
> "Terry Given" <my_name@ieee.org> wrote in message
> news:qypYd.8841$1S4.942601@news.xtra.co.nz...
>
>>Larry Brasfield wrote:
>
> ...
>
>>>A number of op-amps on the market today are
>>>very tolerant of capacitive loading because they
>>>have a feature whereby that loading causes the
>>>gain-bandwidth of the part to drop, almost in
>>>proportion to the loading, such that the extra
>>>pole remains far enough above the unity gain
>>>crossover frequency that stability is preserved.
>>>The LM8261 suggested by Mr. Hill is a good
>>>example of this class.
>>
>>I have been bitten quite badly by a similar "feature" in
>>the LM6134 (its a slew-rate modification).
>
>
> The feature I mentioned above works by causing the
> effective value of an internal capacitance to increase.
> So it changes both the linear small-signal response
> (less GBW) and the slew limiting (slower).

Nah- you're full-o-shyte! The capacitive loading decreases the effective
internal capacitance due to Miller effects because it reduces the gain.
Even a moron like you should realize that less gain means less Miller
effect. You are a pretentious little piss-ant bs mouthpiece who has
never built anything in his life.

>
> The adaptive slewing feature that National (sort
> of) describes in the LM6134 data*** is not the
> same thing at all. It operates by increasing the
> amount of current available for slewing under
> certain large signal input conditions.

Really- S.R. drops to 0V/us at 10n- and settling time goes to hell-
someplace you should consider going too, permanently.

>
> As for the problem you had with it, I would not
> deem it a biting feature so much as a reason to
> not use it without understanding it better. I will
> say, however, that mode changing circuitry for
> the alleged benefit of large signal conditions is
> something that usually gives me the willys.
>

What a crock of pretentious PISS....