Second source horror stories

P

Phil Hobbs

Guest
Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
<sniiiip>
WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the part
virtually useless.

Or not. Of course, one must fully evaluate a
second-source manufacturer's parts, before
committing it to manufacturing.
Click to expand...

Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431. The Diodes Inc version is
super well behaved and stable, as shown in the stability plot on P.7 of
<https://www.diodes.com/assets/Datasheets/TLV431.pdf>.

Ooooonnn the other hand, see ON Semi's (in)stability plot at Figure 18 of
<https://www.onsemi.com/pub/Collateral/TLV431A-D.PDF>

and TI's not-quite-as-bad-but-still-pretty-awful TI version, Figure 18 of
<http://www.ti.com/lit/ds/symlink/tlv431b.pdf>.

The Diodes part is stable for all load capacitances and all output
voltages, provided the anode current is over a milliamp or so.

The other two have horribly complicated behaviour, with the ON Semi part
taking the biscuit with four separate regions of instability.

What are your horror stories?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Phil Hobbs wrote...
Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the part
virtually useless.

Or not. Of course, one must fully evaluate a
second-source manufacturer's parts, before
committing it to manufacturing.

Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

Ooooonnn the other hand, see ON Semi's (in)stability plot ...

and TI's not-quite-as-bad-but-still-pretty-awful version ...
Click to expand...

Wasn't TI the TLV431 originator? I have a 1996 datasheet.


--
Thanks,
- Win
 
On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.
Click to expand...

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 6 Aug 2019 08:51:08 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the part
virtually useless.

Or not. Of course, one must fully evaluate a
second-source manufacturer's parts, before
committing it to manufacturing.


Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431. The Diodes Inc version is
super well behaved and stable, as shown in the stability plot on P.7 of
https://www.diodes.com/assets/Datasheets/TLV431.pdf>.

Ooooonnn the other hand, see ON Semi's (in)stability plot at Figure 18 of
https://www.onsemi.com/pub/Collateral/TLV431A-D.PDF
Click to expand...

I think you win the campfire horror story contest with that one.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...
Click to expand...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John
 
On 8/6/19 9:50 AM, Winfield Hill wrote:
Phil Hobbs wrote...

Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the part
virtually useless.

Or not. Of course, one must fully evaluate a
second-source manufacturer's parts, before
committing it to manufacturing.

Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

Ooooonnn the other hand, see ON Semi's (in)stability plot ...

and TI's not-quite-as-bad-but-still-pretty-awful version ...

Wasn't TI the TLV431 originator? I have a 1996 datasheet.
Click to expand...
I think so--it's sort of the low power version of their hoary old TL431,
the one JT used to use for everything. ;)

The TI one has a nasty stripe of instability right in the range of
capacitors you might want to use.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 6 Aug 2019 11:58:37 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:53 AM, John Larkin wrote:
On Tue, 6 Aug 2019 11:22:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.

Cheers

Phil Hobbs

Having some 22 or 47 uF ceramics in stock is handy lately. Some
switchers want 100 uF or even more.

I often use one of those in parallel with, like, 150 uF AlPo with some
acceptable minimum ESR. You get the lead-lag effect that way.

Since my latest laser board design uses 2.14 MHz switchers without any
spurs being detectable above shot noise even at a 10-Hz IF bandwidth,
I'll probably start using those a lot more. (The spec had a noise limit
from 30 Hz to 2 MHz, so 2.14 was a good number just in case.)

Cheers

Phil Hobbs
Click to expand...

If you are concerned about frequency-domain noise (but not real noise)
the spread-spectrum switchers, like TPS54302, are great.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 8/6/19 8:51 AM, Phil Hobbs wrote:
Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
    WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the
part
virtually useless.

   Or not.  Of course, one must fully evaluate a
   second-source manufacturer's parts, before
   committing it to manufacturing.


Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431.  The Diodes Inc version is
super well behaved and stable, as shown in the stability plot on P.7 of
https://www.diodes.com/assets/Datasheets/TLV431.pdf>.

Ooooonnn the other hand, see ON Semi's (in)stability plot at Figure 18 of
https://www.onsemi.com/pub/Collateral/TLV431A-D.PDF

and TI's not-quite-as-bad-but-still-pretty-awful TI version, Figure 18 of
http://www.ti.com/lit/ds/symlink/tlv431b.pdf>.

The Diodes part is stable for all load capacitances and all output
voltages, provided the anode current is over a milliamp or so.

The other two have horribly complicated behaviour, with the ON Semi part
taking the biscuit with four separate regions of instability.

What are your horror stories?

Cheers

Phil Hobbs
Click to expand...

As an aside, most adjustable shunt regulators, including the TLV431,
work like NPN V_BE multipliers--the cathode current is whatever it takes
to make the FB-anode voltage 1.23 V. Thus to make a 1.23V reference,
you attach FB to cathode.

A couple, the LM4041-ADJ and the LM385, are like PNPs--they keep the
FB-cathode voltage constant. Having both helps a lot with stuff like
floating current limiters.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 8/6/19 11:53 AM, John Larkin wrote:
On Tue, 6 Aug 2019 11:22:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.

Cheers

Phil Hobbs

Having some 22 or 47 uF ceramics in stock is handy lately. Some
switchers want 100 uF or even more.
Click to expand...

I often use one of those in parallel with, like, 150 uF AlPo with some
acceptable minimum ESR. You get the lead-lag effect that way.

Since my latest laser board design uses 2.14 MHz switchers without any
spurs being detectable above shot noise even at a 10-Hz IF bandwidth,
I'll probably start using those a lot more. (The spec had a noise limit
from 30 Hz to 2 MHz, so 2.14 was a good number just in case.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 6 Aug 2019 11:22:58 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.

Cheers

Phil Hobbs
Click to expand...

Having some 22 or 47 uF ceramics in stock is handy lately. Some
switchers want 100 uF or even more.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tue, 6 Aug 2019 11:22:58 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.

Cheers

Phil Hobbs
Click to expand...

180 uF polymer, just to be safe.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
My sister told me about her terrible trip to Hawaii,
Oh wait, different kind of second source!

Mikek
 
On 8/6/19 11:09 AM, Phil Hobbs wrote:
On 8/6/19 9:50 AM, Winfield Hill wrote:
Phil Hobbs wrote...

Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
    WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find
that
those particular specs may be WIDELY different - enough to make the
part
virtually useless.

   Or not.  Of course, one must fully evaluate a
   second-source manufacturer's parts, before
   committing it to manufacturing.

Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431.  The Diodes
Inc version is super well behaved and stable ...

Ooooonnn the other hand, see ON Semi's (in)stability plot ...

and TI's not-quite-as-bad-but-still-pretty-awful version ...

  Wasn't TI the TLV431 originator?  I have a 1996 datasheet.


I think so--it's sort of the low power version of their hoary old TL431,
the one JT used to use for everything. ;)

The TI one has a nasty stripe of instability right in the range of
capacitors you might want to use.

Cheers

Phil Hobbs
Click to expand...

The BJT-based TL431 does seem pretty consistent, even when bought in
bags of 50 no-name from dubious eBay supplier.

The issue with the CMOS ones probably consequence of the cheaper ones
being fabbed with the well-regarded "eh, whatever"-micron process to
exacting tolerances of, ah, y'know. whatever they are.

but if you need 1.2 volts reference instead of 2.5 and lower cathode
current than the 1mA the hoary TL341 likes to have then that's where
you're at I guess
 
On 8/6/19 12:36 PM, John Larkin wrote:
On Tue, 6 Aug 2019 11:58:37 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:53 AM, John Larkin wrote:
On Tue, 6 Aug 2019 11:22:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.

Cheers

Phil Hobbs

Having some 22 or 47 uF ceramics in stock is handy lately. Some
switchers want 100 uF or even more.

I often use one of those in parallel with, like, 150 uF AlPo with some
acceptable minimum ESR. You get the lead-lag effect that way.

Since my latest laser board design uses 2.14 MHz switchers without any
spurs being detectable above shot noise even at a 10-Hz IF bandwidth,
I'll probably start using those a lot more. (The spec had a noise limit
from 30 Hz to 2 MHz, so 2.14 was a good number just in case.)

Cheers

Phil Hobbs

If you are concerned about frequency-domain noise (but not real noise)
the spread-spectrum switchers, like TPS54302, are great.
Click to expand...
Is the spread-spectrum optional? Because it's super useful to be able
to concentrate all the spur power in one spot so I can see it.
Sometimes I do things that require knowing the amplitude statistics of
the noise pretty accurately, and being able to estimate the switcher's
contribution is super helpful.

There are other ways to do that, of course, e.g. trigger a scope off the
switcher and average like mad.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 8/6/19 11:02 AM, John Larkin wrote:
On Tue, 6 Aug 2019 08:51:08 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the part
virtually useless.

Or not. Of course, one must fully evaluate a
second-source manufacturer's parts, before
committing it to manufacturing.


Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431. The Diodes Inc version is
super well behaved and stable, as shown in the stability plot on P.7 of
https://www.diodes.com/assets/Datasheets/TLV431.pdf>.

Ooooonnn the other hand, see ON Semi's (in)stability plot at Figure 18 of
https://www.onsemi.com/pub/Collateral/TLV431A-D.PDF


I think you win the campfire horror story contest with that one.
Click to expand...

For fairness, the original TI TLV271 is a great deal quieter than the
Diodes version, especially in the 1/f region.

Then there's the original LM324 with the single bias network for four
sections (fixed in the Fairchild LM324 and the NS LM324A but not the
Motorola one). Having the bias collapse for all sections when one
rails is not nice, but the independently-biased ones are fine, for very
price-sensitive values of 'fine'. ;)

In my business, the Osram BPW34 photodiode is several times faster (as
well as quieter) than the Vishay one. You wouldn't learn that from their
datasheets.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

In my business, the Osram BPW34 photodiode is several times faster (as
well as quieter) than the Vishay one. You wouldn't learn that from their
datasheets.

Cheers

Phil Hobbs
Click to expand...

Curiuos - how do you measure the noise in a photodiode? This would seem to be
a problem with the op amp and feedback resistor as part of the picture.
 
On 2019/08/06 4:42 p.m., Phil Hobbs wrote:
On 8/6/19 11:02 AM, John Larkin wrote:
On Tue, 6 Aug 2019 08:51:08 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
    WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find
that
those particular specs may be WIDELY different - enough to make the
part
virtually useless.

   Or not.  Of course, one must fully evaluate a
   second-source manufacturer's parts, before
   committing it to manufacturing.


Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431.  The Diodes Inc version is
super well behaved and stable, as shown in the stability plot on P.7 of
https://www.diodes.com/assets/Datasheets/TLV431.pdf>.

Ooooonnn the other hand, see ON Semi's (in)stability plot at Figure
18 of
https://www.onsemi.com/pub/Collateral/TLV431A-D.PDF


I think you win the campfire horror story contest with that one.




For fairness, the original TI TLV271 is a great deal quieter than the
Diodes version, especially in the 1/f region.

Then there's the original LM324 with the single bias network for four
sections (fixed in the Fairchild LM324 and the NS LM324A but not the
Motorola one).   Having the bias collapse for all sections when one
rails is not nice, but the independently-biased ones are fine, for very
price-sensitive values of 'fine'. ;)

In my business, the Osram BPW34 photodiode is several times faster (as
well as quieter) than the Vishay one. You wouldn't learn that from their
datasheets.

Cheers

Phil Hobbs
Click to expand...

TTL had the same problems. Some repair specs required one to use a
particular manufacturers 74(LS)XXX part (TI in most cases) due to 2nd
source irregularities from the original specs.

And I too have seen op-amp circuits that were very fussy about the
manufacturer. TL081 rings a bell for fussy - had to try several (8 to
10) from 2nd source to get one where the circuit would work properly.

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
On 8/6/19 8:27 PM, Steve Wilson wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

In my business, the Osram BPW34 photodiode is several times faster (as
well as quieter) than the Vishay one. You wouldn't learn that from their
datasheets.

Cheers

Phil Hobbs

Curiuos - how do you measure the noise in a photodiode? This would seem to be
a problem with the op amp and feedback resistor as part of the picture.
Click to expand...

There's a bunch of series resistance in the very thin epi layer, like
50-200 ohms. Osram seems to dope theirs more, which helps. With a
really good bootstrap (see e.g. <https://hobbs-eo.com>, the additive
Johnson noise dominates the dark noise. That's the main reason the
QL01B is quieter than the QL01A.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Tue, 6 Aug 2019 19:42:18 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:02 AM, John Larkin wrote:
On Tue, 6 Aug 2019 08:51:08 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Way down the 2SK3018 thread,

On 8/6/19 5:24 AM, Winfield Hill wrote:> Robert Baer wrote...
sniiiip
WARNING. Be advised that every manufacturer of a given part (the
2SK3018 in this case) runs their fab differently, and you may find that
those particular specs may be WIDELY different - enough to make the part
virtually useless.

Or not. Of course, one must fully evaluate a
second-source manufacturer's parts, before
committing it to manufacturing.


Too right--and worth a separate thread of its own, I think.

My favourite horrible example is the TLV431. The Diodes Inc version is
super well behaved and stable, as shown in the stability plot on P.7 of
https://www.diodes.com/assets/Datasheets/TLV431.pdf>.

Ooooonnn the other hand, see ON Semi's (in)stability plot at Figure 18 of
https://www.onsemi.com/pub/Collateral/TLV431A-D.PDF


I think you win the campfire horror story contest with that one.




For fairness, the original TI TLV271 is a great deal quieter than the
Diodes version, especially in the 1/f region.

Then there's the original LM324 with the single bias network for four
sections (fixed in the Fairchild LM324 and the NS LM324A but not the
Motorola one). Having the bias collapse for all sections when one
rails is not nice, but the independently-biased ones are fine, for very
price-sensitive values of 'fine'. ;)
Click to expand...

The original National data sheet had a footnote in 2-point type that
warned against pulling any input below ground. It should have been
more obvious.
 
On Tue, 6 Aug 2019 18:12:06 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 12:36 PM, John Larkin wrote:
On Tue, 6 Aug 2019 11:58:37 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:53 AM, John Larkin wrote:
On Tue, 6 Aug 2019 11:22:58 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 8/6/19 11:07 AM, jrwalliker@gmail.com wrote:
On Tuesday, 6 August 2019 14:51:01 UTC+1, Winfield Hill wrote:
Phil Hobbs wrote...

My favourite horrible example is the TLV431. The Diodes
Inc version is super well behaved and stable ...

It is just about possible to pick shunt capacitor values that ensure
stability of all makes of TLV431 (and Tl431).

John

Sure, assuming that your circuit is okay with 10 uF.

Cheers

Phil Hobbs

Having some 22 or 47 uF ceramics in stock is handy lately. Some
switchers want 100 uF or even more.

I often use one of those in parallel with, like, 150 uF AlPo with some
acceptable minimum ESR. You get the lead-lag effect that way.

Since my latest laser board design uses 2.14 MHz switchers without any
spurs being detectable above shot noise even at a 10-Hz IF bandwidth,
I'll probably start using those a lot more. (The spec had a noise limit
from 30 Hz to 2 MHz, so 2.14 was a good number just in case.)

Cheers

Phil Hobbs

If you are concerned about frequency-domain noise (but not real noise)
the spread-spectrum switchers, like TPS54302, are great.


Is the spread-spectrum optional? Because it's super useful to be able
to concentrate all the spur power in one spot so I can see it.
Sometimes I do things that require knowing the amplitude statistics of
the noise pretty accurately, and being able to estimate the switcher's
contribution is super helpful.

There are other ways to do that, of course, e.g. trigger a scope off the
switcher and average like mad.

Cheers

Phil Hobbs
Click to expand...

It's only a SOT-23/6, so it doesn't have a lot of options. Fixed freq,
always ss.

https://www.dropbox.com/s/d4882nhmihwqw4c/TPS54302b.jpg?raw=1


But it's very nice.
 
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