Shunt Reference Problems

On 17/02/2020 16:43, Phil Hobbs wrote:
On 2020-02-17 04:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and
isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B
references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.




IIRC datasheet temperature coefficient isn't dV/dT, it's Delta V (max
P-P deviation over the specified temperature range)/Delta T.

dV/dT is allowed to be much larger in smaller ranges.  (Offset drift of
amplifiers is specified the same way.)

Cheers

Phil Hobbs
Click to expand...
That's an interesting point - you can read the data sheet that way but
it's not crystal clear.
From the perfectly linear tracking observed so far I don't think the
parts will do any better over a wider range but the cycler can do it so
I'll run the next test over the full -40 to 85 range.

MK
 
On Mon, 17 Feb 2020 11:43:06 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-17 04:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.




IIRC datasheet temperature coefficient isn't dV/dT, it's Delta V (max
P-P deviation over the specified temperature range)/Delta T.

dV/dT is allowed to be much larger in smaller ranges. (Offset drift of
amplifiers is specified the same way.)

Cheers

Phil Hobbs
Click to expand...

Yes. The typical graph on the ADI data sheet has flat parts and steep
parts.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On 2020-02-17 10:31, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 11:12:05 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 09:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK


Be careful about EMI. We are in a high EMI location, and we see all
sorts of strange rectifying effects.

I do wonder how they can guarantee tempco by design not testing, but
sell different tempco grades. Maybe they assume that voltage accuracy
implies tempco. Or maybe all the parts are the same but just the
prices are different.
Click to expand...

Could be. The old National LM121 precision preamp was like that (before
they recycled the part number as a single version of the LM124, the
dogs). When you zeroed out the offset, you also zeroed the drift.
Pretty slick for its day.

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 2/17/20 4:32 AM, Michael Kellett wrote:
On 16/02/2020 21:42, boB wrote:


If slow-ish sample rate, you could use that Microchip 16 bit
differential input A/D  that does a zero offset between every sample.
Higher sample rates at lower resolution I think.  Works really well
for my current sense applications.  It is also I2C though which may or
may not be an issue for you.




Thanks for the suggestion but it isn't the ADC that is the problem -
it's the ADR530B voltage reference - see my reply to JL below.

I have had to fit the entire isolated voltage reference and ADC onto a
tiny board that replaces an 8 pin SOIC part. If I respin the whole board
other solutions are possible - but currently I'm more bothered by the
implications of the ADR530B not meeting pec.

MK
Click to expand...

I see, I skimmed too quickly sorry about that...
 
On Mon, 17 Feb 2020 12:46:20 -0500, bitrex <user@example.net> wrote:

On 2/17/20 4:32 AM, Michael Kellett wrote:
On 16/02/2020 21:42, boB wrote:


If slow-ish sample rate, you could use that Microchip 16 bit
differential input A/D  that does a zero offset between every sample.
Higher sample rates at lower resolution I think.  Works really well
for my current sense applications.  It is also I2C though which may or
may not be an issue for you.




Thanks for the suggestion but it isn't the ADC that is the problem -
it's the ADR530B voltage reference - see my reply to JL below.

I have had to fit the entire isolated voltage reference and ADC onto a
tiny board that replaces an 8 pin SOIC part. If I respin the whole board
other solutions are possible - but currently I'm more bothered by the
implications of the ADR530B not meeting pec.

MK

I see, I skimmed too quickly sorry about that...
Click to expand...

Right. Well, that I2C A/D also has a voltage reference.
I'm not sure how great it is but it seems to be good.

Carry on....
 
On Monday, February 17, 2020 at 6:12:12 AM UTC-5, Michael Kellett wrote:
On 17/02/2020 09:41, jlarkin@.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK
Click to expand...

MK, who is part vendor for these? One of the major U.S.s/UK, I hope.
There is always a concern about mislabeled and falsified parts.
You might think low-cost parts would not be profitable to fake. I'm
not a conspiracy buff, but messing up our supply of reference devices
would be a devious way to mess with manufacturing quality.. ;-)
Cheers, Rich S.
 
On Mon, 17 Feb 2020 12:50:31 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-17 10:31, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 11:12:05 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 09:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK


Be careful about EMI. We are in a high EMI location, and we see all
sorts of strange rectifying effects.

I do wonder how they can guarantee tempco by design not testing, but
sell different tempco grades. Maybe they assume that voltage accuracy
implies tempco. Or maybe all the parts are the same but just the
prices are different.

Could be. The old National LM121 precision preamp was like that (before
they recycled the part number as a single version of the LM124, the
dogs). When you zeroed out the offset, you also zeroed the drift.
Pretty slick for its day.

Cheers

Phil Hobbs
Click to expand...

I once bought a Motorola reference zener that came in a plastic tube
with a signed certificate and a plot of voltage measured over 30 days.
I don't expect that many modern parts are actually temperature tested
on a production basis. They just fly through a test machine.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 2/17/20 1:48 PM, John Larkin wrote:
On Mon, 17 Feb 2020 12:50:31 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-17 10:31, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 11:12:05 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 09:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK


Be careful about EMI. We are in a high EMI location, and we see all
sorts of strange rectifying effects.

I do wonder how they can guarantee tempco by design not testing, but
sell different tempco grades. Maybe they assume that voltage accuracy
implies tempco. Or maybe all the parts are the same but just the
prices are different.

Could be. The old National LM121 precision preamp was like that (before
they recycled the part number as a single version of the LM124, the
dogs). When you zeroed out the offset, you also zeroed the drift.
Pretty slick for its day.

Cheers

Phil Hobbs

I once bought a Motorola reference zener that came in a plastic tube
with a signed certificate and a plot of voltage measured over 30 days.
I don't expect that many modern parts are actually temperature tested
on a production basis. They just fly through a test machine.
Click to expand...

Statistical sampling? Like how they check that (almost all) pills coming
off the assembly line at 1000 units/min have the proper amount of
medication in them from the medicine-injector machine or (almost all)
donut holes are the right diameter, test every Nth unit for sufficiently
large N to apply the CLT and infer the population mean and standard
deviation to some confidence.
 
On Mon, 17 Feb 2020 15:33:27 -0500, bitrex <user@example.net> wrote:

On 2/17/20 1:48 PM, John Larkin wrote:
On Mon, 17 Feb 2020 12:50:31 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-17 10:31, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 11:12:05 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 09:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK


Be careful about EMI. We are in a high EMI location, and we see all
sorts of strange rectifying effects.

I do wonder how they can guarantee tempco by design not testing, but
sell different tempco grades. Maybe they assume that voltage accuracy
implies tempco. Or maybe all the parts are the same but just the
prices are different.

Could be. The old National LM121 precision preamp was like that (before
they recycled the part number as a single version of the LM124, the
dogs). When you zeroed out the offset, you also zeroed the drift.
Pretty slick for its day.

Cheers

Phil Hobbs

I once bought a Motorola reference zener that came in a plastic tube
with a signed certificate and a plot of voltage measured over 30 days.
I don't expect that many modern parts are actually temperature tested
on a production basis. They just fly through a test machine.



Statistical sampling? Like how they check that (almost all) pills coming
off the assembly line at 1000 units/min have the proper amount of
medication in them from the medicine-injector machine or (almost all)
donut holes are the right diameter, test every Nth unit for sufficiently
large N to apply the CLT and infer the population mean and standard
deviation to some confidence.
Click to expand...

Buy 100 small bags of potato chips, and note the labeled weight of the
contents. Then actually weigh the chips. I've done it. None will be
below the advertised weight, but none will be over by more than a
fraction of the weight of the average chip.

After the bags are filled to a fraction-of-a-chip accuracy, and
sealed, every bag is check weighed. I'd expect every pill to be
inspected and weighed too.






--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 2020-02-17, John Larkin <jlarkin@highland_atwork_technology.com> wrote:
On Mon, 17 Feb 2020 15:33:27 -0500, bitrex <user@example.net> wrote:

On 2/17/20 1:48 PM, John Larkin wrote:
On Mon, 17 Feb 2020 12:50:31 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-17 10:31, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 11:12:05 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 09:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK


Be careful about EMI. We are in a high EMI location, and we see all
sorts of strange rectifying effects.

I do wonder how they can guarantee tempco by design not testing, but
sell different tempco grades. Maybe they assume that voltage accuracy
implies tempco. Or maybe all the parts are the same but just the
prices are different.

Could be. The old National LM121 precision preamp was like that (before
they recycled the part number as a single version of the LM124, the
dogs). When you zeroed out the offset, you also zeroed the drift.
Pretty slick for its day.

Cheers

Phil Hobbs

I once bought a Motorola reference zener that came in a plastic tube
with a signed certificate and a plot of voltage measured over 30 days.
I don't expect that many modern parts are actually temperature tested
on a production basis. They just fly through a test machine.



Statistical sampling? Like how they check that (almost all) pills coming
off the assembly line at 1000 units/min have the proper amount of
medication in them from the medicine-injector machine or (almost all)
donut holes are the right diameter, test every Nth unit for sufficiently
large N to apply the CLT and infer the population mean and standard
deviation to some confidence.

Buy 100 small bags of potato chips, and note the labeled weight of the
contents. Then actually weigh the chips. I've done it. None will be
below the advertised weight, but none will be over by more than a
fraction of the weight of the average chip.
Click to expand...

Bags are weighed and fragments added to meet the threshold.

After the bags are filled to a fraction-of-a-chip accuracy, and
sealed, every bag is check weighed. I'd expect every pill to be
inspected and weighed too.
Click to expand...

Pringles aren't done that way they meet the label spec by design
and I expect pills are too.




--
Jasen.
 
On Tue, 18 Feb 2020 04:08:29 -0000 (UTC), Jasen Betts
<jasen@xnet.co.nz> wrote:

On 2020-02-17, John Larkin <jlarkin@highland_atwork_technology.com> wrote:
On Mon, 17 Feb 2020 15:33:27 -0500, bitrex <user@example.net> wrote:

On 2/17/20 1:48 PM, John Larkin wrote:
On Mon, 17 Feb 2020 12:50:31 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-17 10:31, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 11:12:05 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 09:41, jlarkin@highlandsniptechnology.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@highlandsniptechnology.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I?m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK


Be careful about EMI. We are in a high EMI location, and we see all
sorts of strange rectifying effects.

I do wonder how they can guarantee tempco by design not testing, but
sell different tempco grades. Maybe they assume that voltage accuracy
implies tempco. Or maybe all the parts are the same but just the
prices are different.

Could be. The old National LM121 precision preamp was like that (before
they recycled the part number as a single version of the LM124, the
dogs). When you zeroed out the offset, you also zeroed the drift.
Pretty slick for its day.

Cheers

Phil Hobbs

I once bought a Motorola reference zener that came in a plastic tube
with a signed certificate and a plot of voltage measured over 30 days.
I don't expect that many modern parts are actually temperature tested
on a production basis. They just fly through a test machine.



Statistical sampling? Like how they check that (almost all) pills coming
off the assembly line at 1000 units/min have the proper amount of
medication in them from the medicine-injector machine or (almost all)
donut holes are the right diameter, test every Nth unit for sufficiently
large N to apply the CLT and infer the population mean and standard
deviation to some confidence.

Buy 100 small bags of potato chips, and note the labeled weight of the
contents. Then actually weigh the chips. I've done it. None will be
below the advertised weight, but none will be over by more than a
fraction of the weight of the average chip.

Bags are weighed and fragments added to meet the threshold.
Click to expand...

No.

https://en.wikipedia.org/wiki/Multihead_weigher

aka Partial Product Weighing Machine.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On 17/02/2020 18:06, boB wrote:
On Mon, 17 Feb 2020 12:46:20 -0500, bitrex <user@example.net> wrote:

On 2/17/20 4:32 AM, Michael Kellett wrote:
On 16/02/2020 21:42, boB wrote:


If slow-ish sample rate, you could use that Microchip 16 bit
differential input A/D  that does a zero offset between every sample.
Higher sample rates at lower resolution I think.  Works really well
for my current sense applications.  It is also I2C though which may or
may not be an issue for you.




Thanks for the suggestion but it isn't the ADC that is the problem -
it's the ADR530B voltage reference - see my reply to JL below.

I have had to fit the entire isolated voltage reference and ADC onto a
tiny board that replaces an 8 pin SOIC part. If I respin the whole board
other solutions are possible - but currently I'm more bothered by the
implications of the ADR530B not meeting pec.

MK

I see, I skimmed too quickly sorry about that...


Right. Well, that I2C A/D also has a voltage reference.
I'm not sure how great it is but it seems to be good.

Carry on....
Click to expand...
Eventually, when I re-spin the pcb for this power supply I may replace
the reference chip and using the processor's ADC with one of these:
TI ADS122U04,

24 bit ADC with built in 5ppm (actually 30ppm worst case) voltage
reference with typical 110ppm long term drift over 1000 hours and an on
chip temperature sensor. Possible to calibrate over temperature by
simple temperature sweep.
Not sure about the drift - perhaps it'll have to demand re-cal.

MK
 
On 17/02/2020 18:30, Rich S wrote:
On Monday, February 17, 2020 at 6:12:12 AM UTC-5, Michael Kellett wrote:
On 17/02/2020 09:41, jlarkin@.com wrote:
On Mon, 17 Feb 2020 09:27:59 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 16/02/2020 20:37, jlarkin@.com wrote:
On Sun, 16 Feb 2020 14:51:21 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

Does that mean that you are using the ADC in the micro with the ADR as
its reference? Those kinds of ADCs aren't especially accurate, no
matter how good the reference.



Actually the ADC is pretty good, the problem is the ADR530B, as is
proved by measuring it directly both in the complete PSU and on a test
board. Of 6 tested none meet the specified 40ppm/C mac tempco.

MK

I don't think ADI is shipping bad parts. Sounds like some kind of
setup problem.



I wouldn't expect ADI to ship bad parts either - which is why I raise
the subject at all.

The test board setup is so simple that it's rather hard to imagine what
might be wrong with it. Yet the ADR530B parts had beattifully linear but
out of spec temperaure coefficients. And the Microchip LM4040 parts had
rather quirky (but in spec) behaviour.

I had hoped that someone on SED might have experience of good or bad
behaviour of similar shunt references.

I've ordered some ADR250B parts and I'll add them to the same test and
repeat.

MK

MK, who is part vendor for these? One of the major U.S.s/UK, I hope.
There is always a concern about mislabeled and falsified parts.
You might think low-cost parts would not be profitable to fake. I'm
not a conspiracy buff, but messing up our supply of reference devices
would be a devious way to mess with manufacturing quality.. ;-)
Cheers, Rich S.
Click to expand...
They came from RS Components in the UK - if I get to the stage of having
evidence that will convince SED I'll take it up with RS - who probably
have a better hotline to ADI than I do.

MK
 
That's an interesting point - you can read the data sheet that way but
it's not crystal clear.
Click to expand...

The other thing that can cause this is die stress. SC70-package references are fairly famous for that. Routing a U around the reference is a good solution, but of course takes a hit in area and routability.

Cheers

Phil Hobbs
 
On 2/17/20 11:08 PM, Jasen Betts wrote:

Buy 100 small bags of potato chips, and note the labeled weight of the
contents. Then actually weigh the chips. I've done it. None will be
below the advertised weight, but none will be over by more than a
fraction of the weight of the average chip.

Bags are weighed and fragments added to meet the threshold.

After the bags are filled to a fraction-of-a-chip accuracy, and
sealed, every bag is check weighed. I'd expect every pill to be
inspected and weighed too.

Pringles aren't done that way they meet the label spec by design
and I expect pills are too.
Click to expand...

You can design any assembly-line process you like as best you can to
meet the label spec "by design" and I would hope one would, but you
gotta regularly verify that your process is, in fact, meeting the spec!

Neither the pills nor the assembly line is going to tell you if you just
ask them like "hey can I ask you a personal question are all your
parameters within tolerance today?"

Just weighing the pill doesn't give you the whole picture, part of the
drug is medication and part of the pill is binder/other stuff, the
weight could be right but the proportion could be off. The only way to
verify that's right in the case of medication tablets is "destructively
testing" i.e. a chemical analysis and you cant destructively test all
your pills or you got no pills to sell.
 
On Tuesday, February 18, 2020 at 4:07:35 AM UTC-5, Michael Kellett wrote:
On 17/02/2020 18:06, boB wrote:
On Mon, 17 Feb 2020 12:46:20 -0500, bitrex <user@example.net> wrote:

On 2/17/20 4:32 AM, Michael Kellett wrote:
On 16/02/2020 21:42, boB wrote:


If slow-ish sample rate, you could use that Microchip 16 bit
differential input A/D  that does a zero offset between every sample.
Higher sample rates at lower resolution I think.  Works really well
for my current sense applications.  It is also I2C though which may or
may not be an issue for you.




Thanks for the suggestion but it isn't the ADC that is the problem -
it's the ADR530B voltage reference - see my reply to JL below.

I have had to fit the entire isolated voltage reference and ADC onto a
tiny board that replaces an 8 pin SOIC part. If I respin the whole board
other solutions are possible - but currently I'm more bothered by the
implications of the ADR530B not meeting pec.

MK

I see, I skimmed too quickly sorry about that...


Right. Well, that I2C A/D also has a voltage reference.
I'm not sure how great it is but it seems to be good.

Carry on....

Eventually, when I re-spin the pcb for this power supply I may replace
the reference chip and using the processor's ADC with one of these:
TI ADS122U04,

24 bit ADC with built in 5ppm (actually 30ppm worst case) voltage
reference with typical 110ppm long term drift over 1000 hours and an on
chip temperature sensor. Possible to calibrate over temperature by
simple temperature sweep.
Not sure about the drift - perhaps it'll have to demand re-cal.

MK
Click to expand...

Hey just sorta 1/2 lurking on this thread, but did anyone mention
thermal stresses in the pcb... if it's held onto some piece of metal hard
it could be stressed with temperature.

George H.
 
On Mon, 17 Feb 2020 11:19:43 +0000, Michael Kellett <mk@mkesc.co.uk>
wrote:

On 17/02/2020 11:04, speff wrote:
On Sunday, 16 February 2020 09:51:24 UTC-5, Michael Kellett wrote:
I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

The ADR530B Temp Coefficient is specified as 15ppm typical and 40ppm
max. There is a note saying “Guaranteed by design, but not production
tested “ .

When I ran it though a temperature cycle, I was a bit disappointed to
get the results in psu_plot_1.jpg.

https://www.dropbox.com/sh/8f6b34u58gg400r/AABcRqFMQ-Q0JAVOAzFRcxJra?dl=0

For the temperature tests the power supply runs off the mains, its on
board processor reports results to a PC outside the test chamber. The 4
PSU outputs are also monitored by a Keysight 34972A outside the chamber.
I’m not bothered by the actual output voltages – these are dependent on
the cheap and cheerful LM4040s and within spec (although I don’t like
the steps on the blue 15V channel).

The 15 and 5 V measurement errors plots come from comparing the measured
(by 34972A) outputs with the self-reported output based on the ADR530B
references and the temperature drift is much higher than 40ppm.

My first thought was that external parts, probably voltage divider
resistors or maybe even the tiny processor ADC was causing the problem,
so I replaced the resistors with expensive ones and added another 4 x
34972A channels to monitor the ADR530Bs directly.

This got me psu_plot_refs_ltcrs_1.jpg.

There’s still some bad stuff going on with the blue 15V channel – but I
don’t care about that yet – concentrate on the last plot – that’s the 4
ADR530B chips monitored directly, the temperature coefficients over the
5- 60C range work out at:

65, 56, 53, 53 ppm/C.

Well, it could still be my ADC or some other thing I’ve missed in my
design, so I built a little test board with 2 x Microchip LM4040 and 2 x
Analog ADR530B, there’s a picture of it set up in the temperature cycler.

Each ref chip is connected to a common 10V supply by a 2k2 resistor.
Each ref chip is shunted with a 470nF cap.
The results are shown in ref_chips_1.jpg

The temperature coefficients over the 5- 60C range work out at:

-27, 46, 50, 54 ppm/C.

The Microchip parts are within spec but the one with the blue trace has
a seriously odd behaviour (this is NOT the same channel on the 34972A as
the previous “bumpy” LM4040).

The real problem is the ADR530B parts – perfectly linear and smooth
tracking of temperature, and out of spec.

I’ll be following this up with AD (of course) but I’d be interested in
any comments.

MK

In your tests to attempt to isolate the reference- did you have nothing else in the environmental chamber? If the power supply was there, as it appeared to be in the photo, was it operating during the test?

Best regards,
Spehro Pefhany

Good point, thanks - it was there but not plugged in - if you look very
carefully you can see the unnconected IEC mains connector at the bottom
left (and it was unconnected during the test - I checked the testfile
and all the PSU signals are at zero).


I've ordered some similar ADI parts (ADR525B) and I'll add those to the
test board, and maybe a few others - the 34972A has lots of channels !

MK
Click to expand...

Watch the 34972A; You need slow/long measurement period and should
avoid large voltage differences between subsequent measurements.

It pumps current into the measurement nodes at the time of switching
and may also introduce CM loops, though 'isolated' from the internal
meter.

RL
 
On Tuesday, 18 February 2020 17:40:11 UTC, bitrex wrote:

You can design any assembly-line process you like as best you can to
meet the label spec "by design" and I would hope one would, but you
gotta regularly verify that your process is, in fact, meeting the spec!

Neither the pills nor the assembly line is going to tell you if you just
ask them like "hey can I ask you a personal question are all your
parameters within tolerance today?"

Just weighing the pill doesn't give you the whole picture, part of the
drug is medication and part of the pill is binder/other stuff, the
weight could be right but the proportion could be off. The only way to
verify that's right in the case of medication tablets is "destructively
testing" i.e. a chemical analysis and you cant destructively test all
your pills or you got no pills to sell.
Click to expand...

glue em back together. After unreacting them :)


NT
 
On 18/02/2020 21:20, George Herold wrote:
On Tuesday, February 18, 2020 at 4:07:35 AM UTC-5, Michael Kellett wrote:
On 17/02/2020 18:06, boB wrote:
On Mon, 17 Feb 2020 12:46:20 -0500, bitrex <user@example.net> wrote:

On 2/17/20 4:32 AM, Michael Kellett wrote:
On 16/02/2020 21:42, boB wrote:


If slow-ish sample rate, you could use that Microchip 16 bit
differential input A/D  that does a zero offset between every sample.
Higher sample rates at lower resolution I think.  Works really well
for my current sense applications.  It is also I2C though which may or
may not be an issue for you.




Thanks for the suggestion but it isn't the ADC that is the problem -
it's the ADR530B voltage reference - see my reply to JL below.

I have had to fit the entire isolated voltage reference and ADC onto a
tiny board that replaces an 8 pin SOIC part. If I respin the whole board
other solutions are possible - but currently I'm more bothered by the
implications of the ADR530B not meeting pec.

MK

I see, I skimmed too quickly sorry about that...


Right. Well, that I2C A/D also has a voltage reference.
I'm not sure how great it is but it seems to be good.

Carry on....

Eventually, when I re-spin the pcb for this power supply I may replace
the reference chip and using the processor's ADC with one of these:
TI ADS122U04,

24 bit ADC with built in 5ppm (actually 30ppm worst case) voltage
reference with typical 110ppm long term drift over 1000 hours and an on
chip temperature sensor. Possible to calibrate over temperature by
simple temperature sweep.
Not sure about the drift - perhaps it'll have to demand re-cal.

MK

Hey just sorta 1/2 lurking on this thread, but did anyone mention
thermal stresses in the pcb... if it's held onto some piece of metal hard
it could be stressed with temperature.

George H.
Click to expand...
Thanks. Phill Hobbs mentioned that possibility. It would certainly
explain the very odd "jumpy" behaviour of the Microchip LM4040 parts.
I shall run a new test soon with a larger set of parts and over a wider
temperature range.

MK
 
On 19/02/2020 00:59, legg wrote:
On Mon, 17 Feb 2020 11:19:43 +0000, Michael Kellett <mk@mkesc.co.uk
wrote:

On 17/02/2020 11:04, speff wrote:
On Sunday, 16 February 2020 09:51:24 UTC-5, Michael Kellett wrote:
I’m working on a power supply design. It has 4 independent and isolated
channels which use Microchip LM4040 2.5V references. It also has opto
isolated readback for each channel which uses Analog ADR530B references
and a tiny ST micro.

The ADR530B Temp Coefficient is specified as 15ppm typical and 40ppm
max. There is a note saying “Guaranteed by design, but not production
tested “ .

When I ran it though a temperature cycle, I was a bit disappointed to
get the results in psu_plot_1.jpg.

https://www.dropbox.com/sh/8f6b34u58gg400r/AABcRqFMQ-Q0JAVOAzFRcxJra?dl=0

For the temperature tests the power supply runs off the mains, its on
board processor reports results to a PC outside the test chamber. The 4
PSU outputs are also monitored by a Keysight 34972A outside the chamber.
I’m not bothered by the actual output voltages – these are dependent on
the cheap and cheerful LM4040s and within spec (although I don’t like
the steps on the blue 15V channel).

The 15 and 5 V measurement errors plots come from comparing the measured
(by 34972A) outputs with the self-reported output based on the ADR530B
references and the temperature drift is much higher than 40ppm.

My first thought was that external parts, probably voltage divider
resistors or maybe even the tiny processor ADC was causing the problem,
so I replaced the resistors with expensive ones and added another 4 x
34972A channels to monitor the ADR530Bs directly.

This got me psu_plot_refs_ltcrs_1.jpg.

There’s still some bad stuff going on with the blue 15V channel – but I
don’t care about that yet – concentrate on the last plot – that’s the 4
ADR530B chips monitored directly, the temperature coefficients over the
5- 60C range work out at:

65, 56, 53, 53 ppm/C.

Well, it could still be my ADC or some other thing I’ve missed in my
design, so I built a little test board with 2 x Microchip LM4040 and 2 x
Analog ADR530B, there’s a picture of it set up in the temperature cycler.

Each ref chip is connected to a common 10V supply by a 2k2 resistor.
Each ref chip is shunted with a 470nF cap.
The results are shown in ref_chips_1.jpg

The temperature coefficients over the 5- 60C range work out at:

-27, 46, 50, 54 ppm/C.

The Microchip parts are within spec but the one with the blue trace has
a seriously odd behaviour (this is NOT the same channel on the 34972A as
the previous “bumpy” LM4040).

The real problem is the ADR530B parts – perfectly linear and smooth
tracking of temperature, and out of spec.

I’ll be following this up with AD (of course) but I’d be interested in
any comments.

MK

In your tests to attempt to isolate the reference- did you have nothing else in the environmental chamber? If the power supply was there, as it appeared to be in the photo, was it operating during the test?

Best regards,
Spehro Pefhany

Good point, thanks - it was there but not plugged in - if you look very
carefully you can see the unnconected IEC mains connector at the bottom
left (and it was unconnected during the test - I checked the testfile
and all the PSU signals are at zero).


I've ordered some similar ADI parts (ADR525B) and I'll add those to the
test board, and maybe a few others - the 34972A has lots of channels !

MK

Watch the 34972A; You need slow/long measurement period and should
avoid large voltage differences between subsequent measurements.

It pumps current into the measurement nodes at the time of switching
and may also introduce CM loops, though 'isolated' from the internal
meter.

RL
Click to expand...
It's set up sensibly enough and the data doesn't look very symptomatic
of the kind of problems you suggest. At some stage I can try using a DMM
directly connected but that will limit me to testing less than 1 part
per day !

MK
 
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