MIC5270 negative LDO misbehaving...

[Jeroen Belleman]

On 2020-10-08 22:31, John Larkin wrote:

On Thu, 8 Oct 2020 08:56:45 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-10-08 08:15, Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red pill, Neo.




All opamps do that, but in this case the current is exceptionally high
(by the standards I am used to). In the case of, say, LT6242 it is 1pA,
while the LT8262 has 2700000pA -- value high enough to visibly distort
the circuit driving it.

ADC inputs are also outputs--they kick out enough charge to seriously
discombobulate some op amps. That RC on the input is not an optional extra.

I have a fairly swoopy Krohn-Hite tunable filter box with plugins that
I\'d use a lot more if its kickout weren\'t so hideous. Over the years
I\'ve learned to connect the inputs of any new instrument to a scope to
spot problems like that.

Cheers

Phil Hobbs

Zero-offset chopamps often shoot nasty spikes out of their input pins.
The result can be a huge (compared to the specs) DC offset that is a
function of the capacitance that the pins see. That can ruin your
afternoon.

The HP 34401A DVM had ghastly kickout from the VF display. They fixed
it by carefully adjusting the specs and zeroing displayed AC
measurements below some threshold.

Some fix! I suppose H and P were retired by that time.

Jeroen Belleman

 

[John Doe]

1. Piotr Wyderski hijacked the thread from Phil Hobbs.

2. I followed up to Piglet with what is probably a very simple question.

3. Piotr Wyderski trashed that simple question.

 

[George Herold]

On Thursday, October 8, 2020 at 1:56:18 PM UTC-4, Phil Hobbs wrote:

On 2020-10-08 10:39, jlarkin@highlandsniptechnology.com wrote:
On Thu, 8 Oct 2020 09:42:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-10-07 23:30, Steve Wilson wrote:
jlarkin@highlandsniptechnology.com wrote:

On Wed, 7 Oct 2020 20:04:47 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Thanks. The sawtooth happens even at very light loads.

Cheers

Phil Hobbs

I wonder if one edge is an internal RF oscillation, and the other edge
is recovery.

Squegging?

Nah, doesn\'t have a grid leak.

Cheers

Phil Hobbs

The input bypassing would affect that sort of oscillation.




Turned out to be the spikies on the input after all. A 1-ohm resistor
and a 4.7 uF cap fixed it right up. Since the spikes are
nearly-symmetric damped 100 MHz with about 4 cycles visible, I don\'t
know why the 330 ohm bead/1uF cap didn\'t do an even better job, but
apparently it didn\'t

No ringing in RC
GH

Thanks to all for the help.

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

 

[John Larkin]

On Thu, 8 Oct 2020 20:56:56 -0000 (UTC), John Doe
<always.look@message.header> wrote:

1. Piotr Wyderski hijacked the thread from Phil Hobbs.

2. I followed up to Piglet with what is probably a very simple question.

3. Piotr Wyderski trashed that simple question.

Take it to Twitter or Facebook. This is an electronics design forum.

 

[Phil Hobbs]

On 2020-10-08 14:55, John Doe wrote:

Phil Hobbs wrote:

John Doe wrote:
Phil Hobbs wrote:
John Doe wrote:
Phil Hobbs wrote:
Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red
pill, Neo.



As if political zealotry injecting itself into an argument is
cute.

That isn\'t politics, silly--Piotr\'s just teasing you. (Very
gently, I might add.)

You\'ve been labouring under the delusion that just because
something is called an \'input\', all it does is sit there. The
reality is often far different, hence the Matrix reference.

I didn\'t know the \"red pill\" thing came from The Matrix (1999).
Wasn\'t much into it. No time to derive clear meaning from everything
people say on the Internet. Now I know.

Well, you did have time to get ticked off about nothing.

Not having a clear meaning doesn\'t mean no response.

So we gather.

You did seem to be making some progress, but oh well. You join a very
select group (like 3 people) in my killfile.

Cheers

Phil Hobbs

 

[Phil Hobbs]

On 2020-10-08 16:31, John Larkin wrote:

On Thu, 8 Oct 2020 08:56:45 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-10-08 08:15, Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red pill, Neo.




All opamps do that, but in this case the current is exceptionally high
(by the standards I am used to). In the case of, say, LT6242 it is 1pA,
while the LT8262 has 2700000pA -- value high enough to visibly distort
the circuit driving it.

ADC inputs are also outputs--they kick out enough charge to seriously
discombobulate some op amps. That RC on the input is not an optional extra.

I have a fairly swoopy Krohn-Hite tunable filter box with plugins that
I\'d use a lot more if its kickout weren\'t so hideous. Over the years
I\'ve learned to connect the inputs of any new instrument to a scope to
spot problems like that.

Cheers

Phil Hobbs

Zero-offset chopamps often shoot nasty spikes out of their input pins.
The result can be a huge (compared to the specs) DC offset that is a
function of the capacitance that the pins see. That can ruin your
afternoon.

Yup. One reason that I\'m fond of the OPA2188 is that TI opened the
kimono unusually wide. See the TI presentation at
<https://www.electrooptical.net/News/random-resources-from-my-sed-posts/>

My other fave chopamp is the OPA378. At 35 nV, it isn\'t the quietest
thing in the flatband, but it really doesn\'t have any 1/f noise, down to
the 10-microhertz level.

The HP 34401A DVM had ghastly kickout from the VF display. They fixed
it by carefully adjusting the specs and zeroing displayed AC
measurements below some threshold.

Yikes. Some proto-Fiorina, obviously.

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

 

[server]

On Thu, 8 Oct 2020 15:09:24 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Thursday, October 8, 2020 at 1:56:18 PM UTC-4, Phil Hobbs wrote:
On 2020-10-08 10:39, jlarkin@highlandsniptechnology.com wrote:
On Thu, 8 Oct 2020 09:42:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-10-07 23:30, Steve Wilson wrote:
jlarkin@highlandsniptechnology.com wrote:

On Wed, 7 Oct 2020 20:04:47 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Thanks. The sawtooth happens even at very light loads.

Cheers

Phil Hobbs

I wonder if one edge is an internal RF oscillation, and the other edge
is recovery.

Squegging?

Nah, doesn\'t have a grid leak.

Cheers

Phil Hobbs

The input bypassing would affect that sort of oscillation.




Turned out to be the spikies on the input after all. A 1-ohm resistor
and a 4.7 uF cap fixed it right up. Since the spikes are
nearly-symmetric damped 100 MHz with about 4 cycles visible, I don\'t
know why the 330 ohm bead/1uF cap didn\'t do an even better job, but
apparently it didn\'t
No ringing in RC

Exactly. Ferrite beads are tricky. An RC at the input of a regulator
is a reliable lowpass filter. Sometimes you can size the resistor to
absorb some of the power dissipation too.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[John Doe]

This is what I get for asking a simple question...

--
John Larkin <jlarkin@highland_atwork_technology.com> wrote:

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NNTP-Posting-Date: Thu, 08 Oct 2020 19:08:57 -0500
From: John Larkin <jlarkin@highland_atwork_technology.com
Newsgroups: sci.electronics.design
Subject: Re: MIC5270 negative LDO misbehaving
Date: Thu, 08 Oct 2020 17:08:57 -0700
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On Thu, 8 Oct 2020 20:56:56 -0000 (UTC), John Doe
always.look@message.header> wrote:

1. Piotr Wyderski hijacked the thread from Phil Hobbs.

2. I followed up to Piglet with what is probably a very simple question.

3. Piotr Wyderski trashed that simple question.





Take it to Twitter or Facebook. This is an electronics design forum.

 

[John Doe]

Oh joy, now I get to hear about (allegedly) being in Phil Hobbs\' kill file
every time he stumbles over a reply to my post, him (like most people who
publicize their alleged kill files) being technically incapable of
ignoring thread branches...

--
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Path: eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net
Newsgroups: sci.electronics.design
Subject: Re: MIC5270 negative LDO misbehaving
Date: Thu, 8 Oct 2020 20:59:33 -0400
Organization: A noiseless patient Spider
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On 2020-10-08 14:55, John Doe wrote:
Phil Hobbs wrote:

John Doe wrote:
Phil Hobbs wrote:
John Doe wrote:
Phil Hobbs wrote:
Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red
pill, Neo.



As if political zealotry injecting itself into an argument is
cute.

That isn\'t politics, silly--Piotr\'s just teasing you. (Very
gently, I might add.)

You\'ve been labouring under the delusion that just because
something is called an \'input\', all it does is sit there. The
reality is often far different, hence the Matrix reference.

I didn\'t know the \"red pill\" thing came from The Matrix (1999).
Wasn\'t much into it. No time to derive clear meaning from everything
people say on the Internet. Now I know.

Well, you did have time to get ticked off about nothing.

Not having a clear meaning doesn\'t mean no response.


So we gather.

You did seem to be making some progress, but oh well. You join a very
select group (like 3 people) in my killfile.

Cheers

Phil Hobbs

 

[Jasen Betts]

On 2020-10-08, John Doe <always.look@message.header> wrote:

Lasse wrote:

skrev John Doe:
jlarkin wrote:
John Doe wrote:
Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red pill,
Neo.

You need a better translator. I have no idea what \"red pill\" and
\"Neo\" refer to.

All opamps do that, but in this case the current is exceptionally
high (by the standards I am used to). In the case of, say, LT6242
it is 1pA, while the LT8262 has 2700000pA -- value high enough to
visibly distort the circuit driving it.

Looks like another translation problem. How does an input inject
current?

Grab any opamp data sheet and look for the input bias current spec.

Injected into the input? Seems that\'s not what\'s being talked about.

Seems I\'m being told that current is EJECTED from an input, that
current being injected back into an op amp output (that normally drives
the input).

the current can be positive or negative, imagine a large resistor
connected to either supply or ground ...

What current???

I believe what\'s being talked about is an input that normally sucks
current. It doesn\'t output current for any good reason. Probably why it\'s
called an \"input\".

Electron current or conventional current?

To a large extent it the direction depends on what type of silicon the
input is connected to. (or more specifically which terminal of what
type of transistor)

The input accepts signals, the output emits amplified signals. current
flow is not relevant ot those definitions.

--
Jasen.

 

[Jasen Betts]

On 2020-10-08, John Doe <always.look@message.header> wrote:

This troll asks lots of questions, but almost never answers anybody else...

signature content ignored.

untrue, you answer frequently, but the answers rarely have any useful
content.

--
Jasen.

 

[John Doe]

A factless troll...

--
Jasen Betts <usenet@revmaps.no-ip.org> wrote:

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On 2020-10-08, John Doe <always.look@message.header> wrote:
This troll asks lots of questions, but almost never answers anybody else...

signature content ignored.

untrue, you answer frequently, but the answers rarely have any useful
content.

--
Jasen.

 

[John Doe]

Jasen Betts wrote:

John Doe wrote:

I believe what\'s being talked about is an input that normally sucks
current. It doesn\'t output current for any good reason. Probably why it\'s
called an \"input\".

Electron current or conventional current?

To a large extent it the direction depends on what type of silicon the
input is connected to. (or more specifically which terminal of what
type of transistor)

The input accepts signals, the output emits amplified signals. current
flow is not relevant ot those definitions.

I asked a simple, ordinary question about input bias current...

That means the maximum current required at the input is 2700 nano
amps?

The apparently irrelevant convoluted reply was...

It means that this \"infinite impedance non-inverting opamp input\" is
injecting 2.7uA into the circuit connected to it.

The text in quotes is a unique expression, never before used. The word
\"injecting\" is probably also unique in this context. I\'m trying to make sense
of the \"answer\" to my simple, ordinary question.

Do you enjoy being an asshole?

 

[server]

On Fri, 9 Oct 2020 03:05:01 -0000 (UTC), John Doe
<always.look@message.header> wrote:

>This is what I get for asking a simple question...

Ask a question, simple or not, in a thoughtful and polite way, and
people will answer in kind.

Try it.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Fri, 9 Oct 2020 03:21:36 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

On 2020-10-08, John Doe <always.look@message.header> wrote:
Lasse wrote:

skrev John Doe:
jlarkin wrote:
John Doe wrote:
Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red pill,
Neo.

You need a better translator. I have no idea what \"red pill\" and
\"Neo\" refer to.

All opamps do that, but in this case the current is exceptionally
high (by the standards I am used to). In the case of, say, LT6242
it is 1pA, while the LT8262 has 2700000pA -- value high enough to
visibly distort the circuit driving it.

Looks like another translation problem. How does an input inject
current?

Grab any opamp data sheet and look for the input bias current spec.

Injected into the input? Seems that\'s not what\'s being talked about.

Seems I\'m being told that current is EJECTED from an input, that
current being injected back into an op amp output (that normally drives
the input).

the current can be positive or negative, imagine a large resistor
connected to either supply or ground ...

What current???

I believe what\'s being talked about is an input that normally sucks
current. It doesn\'t output current for any good reason. Probably why it\'s
called an \"input\".

Electron current or conventional current?

To a large extent it the direction depends on what type of silicon the
input is connected to. (or more specifically which terminal of what
type of transistor)

The input accepts signals, the output emits amplified signals. current
flow is not relevant ot those definitions.

We need to keep our polarities clear. We use conventional current.

When we say 40 nA flows into pin 12 of U6, we know exactly what is
meant.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Jasen Betts]

On 2020-10-09, John Doe <always.look@message.header> wrote:

Jasen Betts wrote:

John Doe wrote:

I believe what\'s being talked about is an input that normally sucks
current. It doesn\'t output current for any good reason. Probably why it\'s
called an \"input\".

Electron current or conventional current?

To a large extent it the direction depends on what type of silicon the
input is connected to. (or more specifically which terminal of what
type of transistor)

The input accepts signals, the output emits amplified signals. current
flow is not relevant ot those definitions.

I asked a simple, ordinary question about input bias current...

That means the maximum current required at the input is 2700 nano
amps?

The maximum, but the minimum is typically in that ballpark too.

The apparently irrelevant convoluted reply was...

It means that this \"infinite impedance non-inverting opamp input\" is
injecting 2.7uA into the circuit connected to it.

The text in quotes is a unique expression, never before used.

A unique expression. This is how language makes humankind great, it
gives the capability to transfer ideas that that were invented after
the language.

To me it seems that he\'s describing the input of an ideal op-amp.
the quotes are perhaps scare qutes because he knows that he has a real
op-amp, and therefore it\'s not ideal.

The word
\"injecting\" is probably also unique in this context. I\'m trying to make sense
of the \"answer\" to my simple, ordinary question.

I can\'t think of a better word to use, sourcing or supplying are weak
synonyms and don\'t carry the implication that this current is
significanlty changing the behaviour of the circuit (from what it was
designed to do).

> Do you enjoy being an asshole?

Given enough provocation I sometimes do, what\'s your excuse?

--
Jasen.

 

[Jasen Betts]

On 2020-10-09, jlarkin@highlandsniptechnology.com <jlarkin@highlandsniptechnology.com> wrote:

On Fri, 9 Oct 2020 03:21:36 -0000 (UTC), Jasen Betts
usenet@revmaps.no-ip.org> wrote:

On 2020-10-08, John Doe <always.look@message.header> wrote:
Lasse wrote:

skrev John Doe:
jlarkin wrote:
John Doe wrote:
Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red pill,
Neo.

You need a better translator. I have no idea what \"red pill\" and
\"Neo\" refer to.

All opamps do that, but in this case the current is exceptionally
high (by the standards I am used to). In the case of, say, LT6242
it is 1pA, while the LT8262 has 2700000pA -- value high enough to
visibly distort the circuit driving it.

Looks like another translation problem. How does an input inject
current?

Grab any opamp data sheet and look for the input bias current spec.

Injected into the input? Seems that\'s not what\'s being talked about.

Seems I\'m being told that current is EJECTED from an input, that
current being injected back into an op amp output (that normally drives
the input).

the current can be positive or negative, imagine a large resistor
connected to either supply or ground ...

What current???

I believe what\'s being talked about is an input that normally sucks
current. It doesn\'t output current for any good reason. Probably why it\'s
called an \"input\".

Electron current or conventional current?

To a large extent it the direction depends on what type of silicon the
input is connected to. (or more specifically which terminal of what
type of transistor)

The input accepts signals, the output emits amplified signals. current
flow is not relevant ot those definitions.

We need to keep our polarities clear. We use conventional current.

When we say 40 nA flows into pin 12 of U6, we know exactly what is
meant.

That seemed unlikely to be what was meant by \"input that normally
sucks current...\" given how many op-amps source current at their
inputs, including the one under discussion.

When I see some unusual claim on unsenet my thoughts are \"How
copuld the possibly be true?\" Sometimes there is an answer.

--
Jasen.

 

[John Doe]

jlarkin@highlandsniptechnology.com wrote:

John Doe wrote:

This is what I get for asking a simple question...

Ask a question, simple or not, in a thoughtful and polite way, and
people will answer in kind.

Try it.

I did. Scroll up. The response was a wisecrack that completely ignored my
question. When I ask a question, I respect your right to remain silent...

 

[server]

On Fri, 9 Oct 2020 05:43:51 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

On 2020-10-09, jlarkin@highlandsniptechnology.com <jlarkin@highlandsniptechnology.com> wrote:
On Fri, 9 Oct 2020 03:21:36 -0000 (UTC), Jasen Betts
usenet@revmaps.no-ip.org> wrote:

On 2020-10-08, John Doe <always.look@message.header> wrote:
Lasse wrote:

skrev John Doe:
jlarkin wrote:
John Doe wrote:
Piotr Wyderski wrote:
John Doe wrote:

How can an input inject current into a circuit?

Asking this question implies that you have selected the red pill,
Neo.

You need a better translator. I have no idea what \"red pill\" and
\"Neo\" refer to.

All opamps do that, but in this case the current is exceptionally
high (by the standards I am used to). In the case of, say, LT6242
it is 1pA, while the LT8262 has 2700000pA -- value high enough to
visibly distort the circuit driving it.

Looks like another translation problem. How does an input inject
current?

Grab any opamp data sheet and look for the input bias current spec.

Injected into the input? Seems that\'s not what\'s being talked about.

Seems I\'m being told that current is EJECTED from an input, that
current being injected back into an op amp output (that normally drives
the input).

the current can be positive or negative, imagine a large resistor
connected to either supply or ground ...

What current???

I believe what\'s being talked about is an input that normally sucks
current. It doesn\'t output current for any good reason. Probably why it\'s
called an \"input\".

Electron current or conventional current?

To a large extent it the direction depends on what type of silicon the
input is connected to. (or more specifically which terminal of what
type of transistor)

The input accepts signals, the output emits amplified signals. current
flow is not relevant ot those definitions.

We need to keep our polarities clear. We use conventional current.

When we say 40 nA flows into pin 12 of U6, we know exactly what is
meant.

That seemed unlikely to be what was meant by \"input that normally
sucks current...\" given how many op-amps source current at their
inputs, including the one under discussion.

When I see some unusual claim on unsenet my thoughts are \"How
copuld the possibly be true?\" Sometimes there is an answer.

We don\'t say \"sucks current\" for several reasons.

We do say that a device sources or sinks current, when the context is
clear. \"The nfet sinks 3 amps\" is clear, looking at the schematic.

In verbal communications, we need to clearly agree on meaning. Of
directions, polarities, causalities, and time. We use classic English,
what they forced us to learn in grammar school.

\"By 2PM, the transformer had been heating for four hours\" is clear.
It\'s enough to sketch a crude graph.

Sometimes people brought up speaking other languages have problems
expressing or understanding some such English expressions, so it\'s
tricky to talk to them about exactly what happened when, and in what
sequence. Best to draw a diagram to be sure.

Maybe some other languages are more precise about this sort of thing.
I know that some versions of Black English have entirely different
ways of phrasing time sequences. My only Black engineer gets the
standard English version precisely correct. A couple of Latin(x)
engineers sometimes don\'t.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Fri, 9 Oct 2020 06:27:57 -0000 (UTC), John Doe
<always.look@message.header> wrote:

jlarkin@highlandsniptechnology.com wrote:

John Doe wrote:

This is what I get for asking a simple question...

Ask a question, simple or not, in a thoughtful and polite way, and
people will answer in kind.

Try it.

I did. Scroll up. The response was a wisecrack that completely ignored my
question. When I ask a question, I respect your right to remain silent...

There are certainly jerks who post here. When people respond by
escalating, we get another idiotic flame thread.

Such content-free, childish insult fests are easy to spot. They are
usually the same people.

The most powerful and constructive thing you can do is ignore the
jerks. Don\'t play their ugly game.

If you want to talk about real-life opamps, we can do that.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard