Forums

nice little opamp

Started by John Larkin October 15, 2016

http://www.onsemi.com/PowerSolutions/product.do?id=NCS2005

This is rrio, 8 MHz, 32 volts max supply.

It seems to be c-load stable at 1 uF and up, ceramic or tantalum,
which means it can drive bypassed reference rails and low-current
power rails.

It rails clean, so will work as a comparator, but above 20 volt supply
the positive clamp gets a little strange.

40 cents each by the reel.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

45 nV typical 1-Hz noise, though, yikes!

A fave of mine in the low cost/good performance regime is the MC33078, which is a dual with vaguely similar specs. It doesn't work well below 10V total supply, and has a lot of input bias current, but its 1-Hz noise is an order of magnitude less and it's cheaper: under 30 cents for the 8-VSSOP in reels from Digikey.

Cheers

Phil Hobbs
On Sat, 15 Oct 2016 13:24:58 -0700 (PDT), Phil Hobbs
<pcdhobbs@gmail.com> wrote:

>45 nV typical 1-Hz noise, though, yikes!
Noise doesn't matter much in the thing I'm doing now. 47 uF from the output to ground helps, too.
> >A fave of mine in the low cost/good performance regime is the MC33078, which is a dual with vaguely similar specs. It doesn't work well below 10V total supply, and has a lot of input bias current, but its 1-Hz noise is an order of magnitude less and it's cheaper: under 30 cents for the 8-VSSOP in reels from Digikey.
I'll regularly be using these from 3.3 to 24 volts. It's a faster, c-loadable, cheaper version of LM7301, which we have used 46,000 of so far. Threw away maybe $25K. After I finish the design, maybe 34 sheets of schematic, we can review it and maybe replace some single SOT23's with cheap duals. Gotta consider pcb placement and pick-and-place feeders as well as the electricals. Using "universal" c-load high voltage single rrio's is easy. Looks like the cheapest opamp that we have in stock is an LM358, 10 cents for the dual. Horrible amp. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Phil Hobbs wrote...
> > 45 nV typical 1-Hz noise, though, yikes! > > A fave of mine in the low cost/good performance > regime is the MC33078 ... its 1-Hz noise is an > order of magnitude less and it's cheaper: under > 30 cents for the 8-VSSOP in reels from Digikey.
I'm a big fan of SOT-23 op-amps. It's too bad nobody ever adds that package for older dies. -- Thanks, - Win
>I'm a big fan of SOT-23 op-amps. &nbsp;It's too bad
&nbsp;nobody ever adds
>that package for older dies.
ISTM that the popular parts among old cheap designs are usually duals or quads, which took advantage of all the real estate DIP packages afford. (What's the single version of the 324/358?) Cheers Phil Hobbs
On 15 Oct 2016 14:32:25 -0700, Winfield Hill
<hill@rowland.harvard.edu> wrote:

>Phil Hobbs wrote... >> >> 45 nV typical 1-Hz noise, though, yikes! >> >> A fave of mine in the low cost/good performance >> regime is the MC33078 ... its 1-Hz noise is an >> order of magnitude less and it's cheaper: under >> 30 cents for the 8-VSSOP in reels from Digikey. > > I'm a big fan of SOT-23 op-amps. It's too bad > nobody ever adds that package for older dies.
The cheapest single opamp that Mouser shows is 16 cents at 1K. The cheapest dual is 10 cents! -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 15 Oct 2016 14:32:25 -0700, Winfield Hill
<hill@rowland.harvard.edu> wrote:

>Phil Hobbs wrote... >> >> 45 nV typical 1-Hz noise, though, yikes! >> >> A fave of mine in the low cost/good performance >> regime is the MC33078 ... its 1-Hz noise is an >> order of magnitude less and it's cheaper: under >> 30 cents for the 8-VSSOP in reels from Digikey. > > I'm a big fan of SOT-23 op-amps. It's too bad > nobody ever adds that package for older dies.
I've been using the MicroChip MCP629x (x=1-4), which comes in a SOT-23, SO-8, SO-14, and TSSOP-14. Good price, if you can use a million a year. ;-)
On Sat, 15 Oct 2016 12:19:02 -0700, John Larkin wrote:

> http://www.onsemi.com/PowerSolutions/product.do?id=NCS2005 > > This is rrio, 8 MHz, 32 volts max supply. > > It seems to be c-load stable at 1 uF and up, ceramic or tantalum, which > means it can drive bypassed reference rails and low-current power rails. > > It rails clean, so will work as a comparator, but above 20 volt supply > the positive clamp gets a little strange. > > 40 cents each by the reel.
Maybe my PDF reader is altering things, but I see only stability at 1nF load (in both data sheet and cover - feature list). Transient responses are shown with only ~25pF load. The voltage drift is rendering in uV/C, so the "micro" character seems ok. {This is with both xpdf and evince on a linux system). Perhaps you have some information from a source other than your link?
On Sun, 16 Oct 2016 04:36:08 -0000 (UTC), Frank Miles
<fpm@u.washington.edu> wrote:

>On Sat, 15 Oct 2016 12:19:02 -0700, John Larkin wrote: > >> http://www.onsemi.com/PowerSolutions/product.do?id=NCS2005 >> >> This is rrio, 8 MHz, 32 volts max supply. >> >> It seems to be c-load stable at 1 uF and up, ceramic or tantalum, which >> means it can drive bypassed reference rails and low-current power rails. >> >> It rails clean, so will work as a comparator, but above 20 volt supply >> the positive clamp gets a little strange. >> >> 40 cents each by the reel. > >Maybe my PDF reader is altering things, but I see only stability at 1nF >load (in both data sheet and cover - feature list). Transient responses >are shown with only ~25pF load. The voltage drift is rendering in uV/C, >so the "micro" character seems ok. {This is with both xpdf and evince on >a linux system). > >Perhaps you have some information from a source other than your link? >
I experimented with one. It gets a little fuzzy with 10 nF loads, but stabilizes nicely with microfarads. Opamps are fairly unpredictable as regards their c-load behavior. RRO parts are often capacitance tolerant, but it depends on how they do the internal rolloff. Data sheets used to have internal schematics, which is getting rare these days. My ideal opamp is single SOT23, rrio, low noise, low offset, low bias current, fairly fast, c-load tolerant, 3 to 30 volt supply, and cheap. OPA197 is a candidate, but I haven't tested it yet. It's 67 cents in reel quantity. The EMI filtering is nice. It works down to 4.5 volts and can output +-40 mA, so it might be worth another 30 cents. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Sun, 16 Oct 2016 09:49:26 -0700, John Larkin wrote:

> On Sun, 16 Oct 2016 04:36:08 -0000 (UTC), Frank Miles > <fpm@u.washington.edu> wrote: > >>On Sat, 15 Oct 2016 12:19:02 -0700, John Larkin wrote: >> >>> http://www.onsemi.com/PowerSolutions/product.do?id=NCS2005 >>> >>> This is rrio, 8 MHz, 32 volts max supply. >>> >>> It seems to be c-load stable at 1 uF and up, ceramic or tantalum, >>> which means it can drive bypassed reference rails and low-current >>> power rails. >>> >>> It rails clean, so will work as a comparator, but above 20 volt supply >>> the positive clamp gets a little strange. >>> >>> 40 cents each by the reel. >> >>Maybe my PDF reader is altering things, but I see only stability at 1nF >>load (in both data sheet and cover - feature list). Transient responses >>are shown with only ~25pF load. The voltage drift is rendering in uV/C, >>so the "micro" character seems ok. {This is with both xpdf and evince >>on a linux system). >> >>Perhaps you have some information from a source other than your link? >> >> > I experimented with one. It gets a little fuzzy with 10 nF loads, but > stabilizes nicely with microfarads.
Ah, from testing. Seems similar to some of the TLx431 family loading zones. Hopefully OnSemi won't change their process on you mid-production, continuing to meet their specs but not your expectations.
> Opamps are fairly unpredictable as regards their c-load behavior. RRO > parts are often capacitance tolerant, but it depends on how they do the > internal rolloff. Data sheets used to have internal schematics, which is > getting rare these days.
Sad. But as long as we buy the devices, the manufacturers will continue to do this (and probably continue making data sheets less comprehensive).
> My ideal opamp is single SOT23, rrio, low noise, low offset, low bias > current, fairly fast, c-load tolerant, 3 to 30 volt supply, and cheap.
And low power consumption, and guaranteed availability for ____ time. Please let us all know when you find this part!
> OPA197 is a candidate, but I haven't tested it yet. It's 67 cents in > reel quantity. The EMI filtering is nice. It works down to 4.5 volts and > can output +-40 mA, so it might be worth another 30 cents.
At least this data sheet shows more information regarding C-load behavior. Thanks, Frank