MIC5270 negative LDO misbehaving...

[legg]

On Wed, 7 Oct 2020 15:42:01 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

So I have this little power supply board, which is sort of a collection
of our previous solutions to weird power supply needs, mainly needing
very quiet supplies.

It uses an LMR23630 sync buck at 2.1 MHz to make +12 from +24, which is
good for a couple of amps. Its output feeds a 450-kHz AOZ1282CI async
buck making -16.

There are linears and cap multipliers to make +15, -12, quiet +-15,
quiet +-5, and one or two others.

It all works very nicely except that the Micrel MIC5270YM5 LDO making
-12V produces an irregular sawtooth about a volt p-p which nothing seems
to fix.

Hanging a 300-ohm load on it makes the sawtooth speed up. That\'s
expected, because once the pass transistor kicks it out of regulation,
the capacitor has to bleed down until it happens again, and that happens
much faster with a load.

1 nF and 10 nF caps from output to FB don\'t help.

I thought it might be the switching spikes on the input confusing it. A
330-ohm high current bead (BLMAG331SN1) and a 1-uF bypass on the input
knocked the spikes down pretty well but didn\'t help the oscillation.

The part is specified for ceramic output caps of at least 1 uF, and the
datasheet claims that the value can be increased without limit. I tried
4.7 uF and 1 uF, both with good C(V) curves so that the actual
capacitance was reasonably well known. Didn\'t help.

I tried changing chips, but that made no difference.

Micrel brags about how stable and quiet the chip is, so presumably it
works in some regimes--in fact we use it in another gizmo to make -4
from -5 to -6, and it works fine. Apparently this lulled me into a
false sense of security.

Razza frazza $#@*!!!

Cheers

Phil Hobbs

What\'s the input? You have a couple of negative rails
mentioned, that could be candidates.

This chip DOES have a thermal limiter; though I doubt it\'s
very fast, there\'s no reason for IT to be stable - not in
IT\'s job description.

Rated at ~160mW with Tlead ~ 85C.

RL

 

[server]

On Thu, 8 Oct 2020 09:38:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-10-08 09:23, John Doe wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> 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.

ADC inputs are also outputs

What does that look like?

Nasty nanosecond spikes of up to tens of picocoulombs. The internal
sampling cap of the ADC gets switched onto the input terminal, so it
charges up in a hurry. The capacitance is often 10-40 pF, so this is
not an inconsiderable amount of current.

With those RRIO amps JL was talking about, the big current pulse can
cause them to lose control of their outputs and dump a bunch of charge
into their internal compensation caps, so that they\'re confused for
microseconds.

Cheers

Phil Hobbs

Not just RRIOs. Classic amps with buried compensation nodes would go
bonkers when hit with a charge spike from an ADC.

You can add an R-C after the opamp, if you don\'t mind what it does.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Thu, 8 Oct 2020 12:35:16 -0000 (UTC), John Doe
<always.look@message.header> wrote:

Piotr Wyderski <peter.pan@neverland.mil> 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.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[legg]

On Wed, 7 Oct 2020 15:42:01 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

So I have this little power supply board, which is sort of a collection
of our previous solutions to weird power supply needs, mainly needing
very quiet supplies.

It uses an LMR23630 sync buck at 2.1 MHz to make +12 from +24, which is
good for a couple of amps. Its output feeds a 450-kHz AOZ1282CI async
buck making -16.

There are linears and cap multipliers to make +15, -12, quiet +-15,
quiet +-5, and one or two others.

It all works very nicely except that the Micrel MIC5270YM5 LDO making
-12V produces an irregular sawtooth about a volt p-p which nothing seems
to fix.

Hanging a 300-ohm load on it makes the sawtooth speed up. That\'s
expected, because once the pass transistor kicks it out of regulation,
the capacitor has to bleed down until it happens again, and that happens
much faster with a load.

1 nF and 10 nF caps from output to FB don\'t help.

I thought it might be the switching spikes on the input confusing it. A
330-ohm high current bead (BLMAG331SN1) and a 1-uF bypass on the input
knocked the spikes down pretty well but didn\'t help the oscillation.

The part is specified for ceramic output caps of at least 1 uF, and the
datasheet claims that the value can be increased without limit. I tried
4.7 uF and 1 uF, both with good C(V) curves so that the actual
capacitance was reasonably well known. Didn\'t help.

I tried changing chips, but that made no difference.

Micrel brags about how stable and quiet the chip is, so presumably it
works in some regimes--in fact we use it in another gizmo to make -4
from -5 to -6, and it works fine. Apparently this lulled me into a
false sense of security.

Razza frazza $#@*!!!

Cheers

Phil Hobbs

Just looking at the data sheet for this thing - it
describes a non-existed enable line. The unused
pins are supposed to be NC.

I\'d look for similar parts that DO have an enable
line, identify the pin (only pin1 is left in the
adjustible version), and treat it as such on
this part, wiring it \'on\' (even if it doesn\'t have
one). Somebody may be cutting down on binning costs.

Three terminal regulators have also demonstrated
sensitivity to the value of resistors in the
feedback string. Micrel/Microchip doesn\'t specify
a prefered value on specs, but you might see what
an order of magnitude does.

RL

 

[server]

On Thu, 8 Oct 2020 04:59:42 -0500, \"Tim Williams\"
<tiwill@seventransistorlabs.com> wrote:

\"Phil Hobbs\" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
news:193da1c7-de94-c7c3-43db-d8680951a4fd@electrooptical.net...
Loop instability usually leads to oscillation at some frequency near the
unity gain cross, with a fairly well-defined period and a distorted
sinusoidal waveform.

This one is a sawtooth whose frequency depends very strongly on the load,
and whose waveform is very far from periodic. That\'s why I was looking
for some interaction with the (much faster) switching junk on the LDO\'s
input.

Often when this happens, it\'s because the crossover is much higher (low
MHz?), and the poles are so far right that it overshoots deep into cutoff.
So you end up with a relaxation oscillator. You have to load it hard enough
(whether by brute-force load current to get it back to threshold sooner, or
with a big enough cap (give or take ESR?) to absorb the huge output current
peak) that that nonlinearity goes away and the actual loop response becomes
apparent.

That\'s the usual thing with LDOs (sometimes it\'s even in the datasheet, you
often see a sawtooth bounce on the light-load transient plot), and a lot of
other regulators (I\'ve seen it plenty of times with TL431 regulated
flybacks). But if you can\'t load it (or unload it, for that matter) enough
to get into the near-linear range, that\'s a bit of a problem...

Also, it seems to be bipolar, so RF rectification isn\'t a bad guess.

On an only somewhat related note, I\'ve see integrated switching regs that
went cuckoo under induced noise. Specifically, a few kV of 1.5/50us surge,
in a wiring harness an inch above the board. Those were some oddball
regulator from Intel (via acquisition from a brand I don\'t remember), high
frequency, integrated inductor, tiny. Best I can tell, the ADJ pin (which
was hardly exposed on the board, maybe 0.01pF to the offending wire?) was
sensitive to that tiniest bit of overvoltage and shut itself down. Symptom
was, CPU resetting erratically. Great, huh?...

Tim

Didn\'t Intel once try putting switching regs on their CPU chips? I
vaguely remember something like that.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Phil Hobbs]

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.

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

 

[Phil Hobbs]

On 2020-10-08 10:57, jlarkin@highlandsniptechnology.com wrote:

On Thu, 8 Oct 2020 08:43:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-10-07 16:40, John Larkin wrote:
On Wed, 7 Oct 2020 15:42:01 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

So I have this little power supply board, which is sort of a collection
of our previous solutions to weird power supply needs, mainly needing
very quiet supplies.

It uses an LMR23630 sync buck at 2.1 MHz to make +12 from +24, which is
good for a couple of amps. Its output feeds a 450-kHz AOZ1282CI async
buck making -16.

There are linears and cap multipliers to make +15, -12, quiet +-15,
quiet +-5, and one or two others.

It all works very nicely except that the Micrel MIC5270YM5 LDO making
-12V produces an irregular sawtooth about a volt p-p which nothing seems
to fix.

We\'ve seen that, a linear reg making sawtooths. I think we used some
other Micrel reg that was bad news.

Maybe the current limiter circuit is less well-designed than the main
loop?


Hanging a 300-ohm load on it makes the sawtooth speed up. That\'s
expected, because once the pass transistor kicks it out of regulation,
the capacitor has to bleed down until it happens again, and that happens
much faster with a load.

1 nF and 10 nF caps from output to FB don\'t help.

I thought it might be the switching spikes on the input confusing it. A
330-ohm high current bead (BLMAG331SN1) and a 1-uF bypass on the input
knocked the spikes down pretty well but didn\'t help the oscillation.

The part is specified for ceramic output caps of at least 1 uF, and the
datasheet claims that the value can be increased without limit. I tried
4.7 uF and 1 uF, both with good C(V) curves so that the actual
capacitance was reasonably well known. Didn\'t help.

I tried changing chips, but that made no difference.

Micrel brags about how stable and quiet the chip is, so presumably it
works in some regimes--in fact we use it in another gizmo to make -4
from -5 to -6, and it works fine. Apparently this lulled me into a
false sense of security.

Razza frazza $#@*!!!


Did you try the Williams stabilization technique, namely using a huge
aluminum lytic?

The board is only 35 mm square and needs to be heatsinked via a gap pad,
so there\'s not a lot of space for BFCs, more\'s the pity.


Here\'s my latest idea about supplies for my DDG rev C.

https://www.dropbox.com/s/gu9fsljyju558w4/P505C_Regs_1.jpg?raw=1

Nice.

There are a few half-erased areas, which I also used to suffer from. I
swear by my Staedtler plug-in electric eraser--$15 on eBay some years
back, and an excellent investment. If you haven\'t used one, it\'ll
change your life. The little battery-powered ones are useless by
comparison.


Oh, I have an AC-powered electric eraser and an electric pencil
sharpener. That sketch would make a superb blue-line copy, but it\'s a
lot easier to photograph with a cell phone camera, drawing lying on
the floor. We\'re still working mostly by email.

I have a long USB cable on my phone that lets me shoot drawings and my
whiteboard without disconnecting from my PC. It won\'t quite reach my
scopes.

I like to draw on vellum, at my drafting table in the big window. It\'s
functional enough.

I\'m going to re-do a lot of that later this morning. Too many
possibilities. Someone pointed out the the optional OCXO can pull a
full amp during warmup. Fixing that of course cascades in all
directions. We have a lot of switched +5 available, so I guess I\'ll do
a home-made LDO to make 3.3Q, the quiet 3.3 supply.


Designing this is like solving a 7-sided Rubics cube in the dark. I\'ll
have 17 regulator chips, four of them duals, and a couple of
references.

The big Zynq is rude and crude and draws nasty current bursts as code
executes. The +1 volt switcher was oscillating at 80 KHz and made the
Arms intermittent. The trigger FPGA is super sensitive to supply
noise. Both have sequencing rules. There are thermal issues. The
pick-and-place machine has run out of feeder slots, so I can\'t just
add a lot of parts.

A couple of places, we are using a 56uF polymer cap in series with a 1
ohm resistor, as a damper. That\'s crazy but works.

I\'ve done that sort of thing too. The problem usually is finding a
resistor which has an adequate pulse rating, in case somebody shorts the
output or connects the box to a car battery.


Switchers driving switchers have fun negative-resistance issues.

My LTM8078 positive to dual negative switcher idea has occasional
hangup issues too. Not in Spice of course. Hence the 79M05 and the
question mark.

Not complaining, of course.

Naturally not. Building gizmos is such fun that it\'s fairly easy to
take difficulties in stride.

Power supplies are pretty close to grunt work, with hazards. There\'s
no eureka-mode upside to getting them right.

Tell me about it.

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 Doe]

jlarkin@highlandsniptechnology.com wrote:

John Doe <always.look@message.header> wrote:
Piotr Wyderski <peter.pan@neverland.mil> 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).

 

[Phil Hobbs]

On 2020-10-08 10:21, 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.

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

 

[Lasse Langwadt Christensen]

torsdag den 8. oktober 2020 kl. 20.13.02 UTC+2 skrev John Doe:

jlarkin@highlandsniptechnology.com wrote:

John Doe <always.look@message.header> wrote:
Piotr Wyderski <peter.pan@neverland.mil> 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 ...

 

[John Doe]

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.

 

[John Doe]

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\".

 

[Piotr Wyderski]

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\".

Dude, get a life...

Piotr

 

[Lasse Langwadt Christensen]

torsdag den 8. oktober 2020 kl. 21.02.15 UTC+2 skrev John Doe:

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\".

are you serious?

 

[John Doe]

What an incredibly useless reply...

--
Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

X-Received: by 2002:ac8:f5c:: with SMTP id l28mr9700860qtk.98.1602184127057; Thu, 08 Oct 2020 12:08:47 -0700 (PDT)
X-Received: by 2002:a37:e43:: with SMTP id 64mr8052254qko.466.1602184126836; Thu, 08 Oct 2020 12:08:46 -0700 (PDT)
Path: eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!news.uzoreto.com!tr1.eu1.usenetexpress.com!feeder.usenetexpress.com!tr3.iad1.usenetexpress.com!border1.nntp.dca1.giganews.com!nntp.giganews.com!news-out.google.com!nntp.google.com!postnews.google.com!google-groups.googlegroups.com!not-for-mail
Newsgroups: sci.electronics.design
Date: Thu, 8 Oct 2020 12:08:46 -0700 (PDT)
In-Reply-To: <rlnnnf$pb1$6@dont-email.me
Complaints-To: groups-abuse@google.com
Injection-Info: google-groups.googlegroups.com; posting-host=77.213.96.51; posting-account=mW5JKwkAAAAMyuWOVeLp8yffyAkVx0g7
NNTP-Posting-Host: 77.213.96.51
References: <0cb9954e-68a9-b76f-5cb9-066776ee665f@electrooptical.net> <rlle6t$187ol$1@portraits.wsisiz.edu.pl> <rlmc1j$6qb$1@dont-email.me> <rlmfq2$qlj$1@dont-email.me> <rlmgiu$1q9aq$1@portraits.wsisiz.edu.pl> <rlmp40$jt2$1@dont-email.me> <rlmvst$1r26a$1@portraits.wsisiz.edu.pl> <rln123$7j8$1@dont-email.me> <m3funfpcphv1sanpnvgtj60tumhts95kr4@4ax.com> <rlnkr4$pb1$1@dont-email.me> <d0570da8-ab04-4462-b249-4ac43ce5fc36o@googlegroups.com> <rlnnnf$pb1$6@dont-email.me
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <224d1306-8502-4cf7-84df-f9dfd9f4350ao@googlegroups.com
Subject: Re: MIC5270 negative LDO misbehaving
From: Lasse Langwadt Christensen <langwadt@fonz.dk
Injection-Date: Thu, 08 Oct 2020 19:08:47 +0000
Content-Type: text/plain; charset=\"UTF-8\"
Lines: 42
Xref: reader02.eternal-september.org sci.electronics.design:610007

torsdag den 8. oktober 2020 kl. 21.02.15 UTC+2 skrev John Doe:
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\".

are you serious?

 

[John Doe]

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

--
Piotr Wyderski <peter.pan@neverland.mil> wrote:

Path: eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!goblin3!goblin.stu.neva.ru!wsisiz.edu.pl!.POSTED.h82-143-146-166-static.e-wro.net.pl!not-for-mail
From: Piotr Wyderski <peter.pan@neverland.mil
Newsgroups: sci.electronics.design
Subject: Re: MIC5270 negative LDO misbehaving
Date: Thu, 8 Oct 2020 21:05:13 +0200
Organization: http://www.wit.edu.pl
Message-ID: <rlnntb$1s30s$1@portraits.wsisiz.edu.pl
References: <0cb9954e-68a9-b76f-5cb9-066776ee665f@electrooptical.net> <rlle6t$187ol$1@portraits.wsisiz.edu.pl> <rlmc1j$6qb$1@dont-email.me> <rlmfq2$qlj$1@dont-email.me> <rlmgiu$1q9aq$1@portraits.wsisiz.edu.pl> <rlmp40$jt2$1@dont-email.me> <rlmvst$1r26a$1@portraits.wsisiz.edu.pl> <rln123$7j8$1@dont-email.me> <m3funfpcphv1sanpnvgtj60tumhts95kr4@4ax.com> <rlnkr4$pb1$1@dont-email.me> <d0570da8-ab04-4462-b249-4ac43ce5fc36o@googlegroups.com> <rlnnnf$pb1$6@dont-email.me
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Thu, 8 Oct 2020 19:05:15 -0000 (UTC)
Injection-Info: portraits.wsisiz.edu.pl; posting-host=\"h82-143-146-166-static.e-wro.net.pl:82.143.146.166\"; logging-data=\"1969180\"; mail-complaints-to=\"abuse@wsisiz.edu.pl\"
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1
In-Reply-To: <rlnnnf$pb1$6@dont-email.me
Content-Language: en-US
Xref: reader02.eternal-september.org sci.electronics.design:610006

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\".

Dude, get a life...

Piotr

 

[legg]

On Thu, 8 Oct 2020 12:08:46 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

torsdag den 8. oktober 2020 kl. 21.02.15 UTC+2 skrev John Doe:
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\".

are you serious?

With JD blocked, I miss these amusing tid-bits.

RL

 

[John Doe]

Here we have a half witted troll (unable to ignore a thread branch,
therefore it stumbles over replies to people it allegedly ignores) saying
it is amused by a three-word practically meaningless, unhelpful, retort...

--
legg <legg@nospam.magma.ca> wrote:

Path: eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: legg <legg@nospam.magma.ca
Newsgroups: sci.electronics.design
Subject: Re: MIC5270 negative LDO misbehaving
Date: Thu, 08 Oct 2020 16:22:21 -0400
Organization: A noiseless patient Spider
Lines: 50
Message-ID: <e6tunf5qrlguk8dh1fmc0reitqoou0evtt@4ax.com
References: <rlle6t$187ol$1@portraits.wsisiz.edu.pl> <rlmc1j$6qb$1@dont-email.me> <rlmfq2$qlj$1@dont-email.me> <rlmgiu$1q9aq$1@portraits.wsisiz.edu.pl> <rlmp40$jt2$1@dont-email.me> <rlmvst$1r26a$1@portraits.wsisiz.edu.pl> <rln123$7j8$1@dont-email.me> <m3funfpcphv1sanpnvgtj60tumhts95kr4@4ax.com> <rlnkr4$pb1$1@dont-email.me> <d0570da8-ab04-4462-b249-4ac43ce5fc36o@googlegroups.com> <rlnnnf$pb1$6@dont-email.me> <224d1306-8502-4cf7-84df-f9dfd9f4350ao@googlegroups.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Injection-Info: reader02.eternal-september.org; posting-host=\"008aa8abe7cfcb79c3852a9c2c89aa67\"; logging-data=\"14580\"; mail-complaints-to=\"abuse@eternal-september.org\"; posting-account=\"U2FsdGVkX18GG23w99Wy9cxm4FiTzGCs\"
Cancel-Lock: sha1:vD1erBdqxzm9HH/gkoMEhCNfA8U=
X-Newsreader: Forte Agent 4.2/32.1118
Xref: reader02.eternal-september.org sci.electronics.design:610014

On Thu, 8 Oct 2020 12:08:46 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

torsdag den 8. oktober 2020 kl. 21.02.15 UTC+2 skrev John Doe:
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\".

are you serious?

With JD blocked, I miss these amusing tid-bits.

RL

 

[John Larkin]

On Thu, 8 Oct 2020 19:02:07 -0000 (UTC), 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\".

If an opamp has PNP transistors first, which many do, its input pins
source current out to the world.

I think the reference was to the opamp injecting current into the
external circuit.

People get so worked up about words, and often don\'t understand the
physics.

 

[John Larkin]

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.