LM399/ADR1399

[miro123]

I added isolation transformer manly to filter medium frequency conducted EMI from the  grid. The HF is filtered from the common mode filter.
There are plenty of noise nowadays.
  - automatic street lighting systems - very dominant here
  - powerline communication.
  - all my home appliance  - Yest I already "upgraded" my home with class A++ BLDC refrigerator and washing machine
  - solar inverters - haply I'm the only one in the neighbor who has PV system

What are the problems if i connect many devices behind single insulation transformer?  I only know that inrush current & THD of consumers can be an issue. I can easily check this with power analyzer.




 

[miro123]

Almost finishing the electrical part of breadboard.
Connection seems to work
6xLM399 -> ADS1256 -> STM32H753 ->ISO_UART-> rapsperry PI

The good news is that 6 LM399s are within 20mV range.  It is nice feeling to see ADS1256 entering areas  where is designed for - measuring small differential DC signals!
My knowledge and expertise lays in digital processing and embedded software. Still a lot of thinks ToDo  hardware related
To Do list
1. Finish mechanical part using the breadboard
2. Update Altium schematics
3. Make and order PCB
4. Mechanical tasks - a lot
============
Start finally with firmware /software.

[Andreas]

Hello,

I would use sockets that better fit to the wire diameter of the LM399.
Better would be soldering direct to the PCB.

Btw: where did you get those NOS (National Semiconductor) LM399?

with best regards

Andreas

[miro123]

Thanks for the tip.
I'm still in prototype phase. I will make final 4 layer PCB  then I will solder them. Circuit is AD1399 ready. Probably I will have two of them when PCB is ready. The plan to install two ADR1399 and 4 LM399.
NOS LMs are form eBay.I'm sure that they are original. I have internal information.  Personally I will not buy lm399 even if they are good one. ADR1399 seems the logical choice nowadays
https://www.ebay.com/itm/173362279991

[oz2cpu]

Questions
the popcorn noise is normal for LM399 ? on almost all units ?
popcorn noise is compleetly gone in ADR1399 ? or just as normal ?
cant it be removed with a slow low-pass filter ?

please clarify ?
and also what device would you recommend of the two ?
they cost about the same, as far as i see

[Kleinstein]

The popcorn noise seems to be normal for the LM399. At least most units show popcorn noise. For the 4 units I tested so far the amplitude was about the same (some 4-5 µV) and just the frequency of steps different. From curves I have seen of other units the behavious fits that picture.
So from what I have see, expect a similar level of popcorn noise for >90% of the units.  One may get times of 1 hour without a jump, but this still does not mean no popcorn noise.

There is no way to filter the popcorn noise with a simple low pass, as the frequency can be very low (like on average around 1 min to 1 hour between steps). With multiple units here may be a chance to get some kind of detector to decide whether the refs are more in there upper or lower state. However chances are this would not be 100% reliable, but it could still reduce the uncertainy quite a bit.

Another way would be taking a histogram and than with enough time get 2 more frequent values and use the 2 values as reference point and not the average.

Besides the popcorn noise there may be other 1/f noise.

I would not expect the popcorn noise to be completely gone with the ADC1399, but the steps size should be smaller (e.g. 1/2)  to get the lower noie level and chances are the steps may be more frequent to get faster averaging.

The ADR1399 is supposedly quite a bit lower noise and chances are the stability can be similar. However so far there is naturally not as much data on long term drift so to be on the safe side with long term drift the LM399 would still be the best bet.

[Andreas]

Hello,

popcorn noise is normal (for all references).
Some samples have more others less (or even invisible) popcorn noise.
-> you should select the devices for low and rare popcorn noise.
Popcorn noise is random. Filtering is impossible since the time between events is unknown.
So even devices that have been tested with no popcorn noise may develop some at certain temperatures or over time.

The ADR1399 is relatively "new" so unknown long term behaviour compared with LM399.
The ADR1399 needs more zener current.
The ADR1399 has less 1/f noise.
The ADR1399 has less zener impedance and is more critical for oscillations.

So it depends on your needs.

with best regards

Andreas

[Kleinstein]

Selecting for the frequency of the popcorn events is a 2 sided thing. On the short time the less often jumping ref looks better, but on a longer term average the more frequent jumping ref can be preferable, as the jump part can average out. It depends on the application which case of preferable.

The zener current for the LM1399 is higher, but it is still relatively low compared to the heater current. With the lower zener impedance the higher current does not translate to a more critical resistor to set the current.

[floobydust]

What is the ADR1399 oscillation mechanism? Datasheet:
"One of the trade-offs of achieving the much reduced dynamic impedance, however, is an increased sensitivity to direct capacitive loading. The LM399 was stable with practically any capacitive load.
The ADR1399 starts to ring with direct capacitive loads of more than a few hundred pF, and oscillates with 10nF direct. The ADR1399 is optimized for an external compensation series network of 5Ω and 1μF, as is shown in most of the typical application figures (see the Typical Applications section). If updating a legacy design with too much capacitance for the ADR1399, and there is nowhere to add a series 5Ω, try reducing the capacitance to less
than 1nF. Another single-element passive found to work directly with ADR1399 is a 10μF tantalum capacitor, even though the series ohms can measure less than 5Ω on an impedance analyzer."

If its zener has a much sharper knee, ADR1399 dynamic impedance 0.04-0.08Ω (but includes comp. network) compared to LM399 0.5-1Ω, where is the (greater) negative resistance coming from?
Oscillation issue with antique gas tube references like 0B2 adding a large capacitor >0.1μF across it causes oscillation, so only a small cap 0.01μF is used to attenuate HF noise. But this is due to Townsend avalanche multiplication.

I believe there was terrible disagreement here about having a large capacitor across a ref zener.  The minus was argued to be higher noise currents (capacitive discharge spikes) knocking out defect atoms in the lattice causing an aging issue. If my take on it is correct, it makes sense and the compensation network might then be a problem?

[Andreas]

Hmm,

My opinion is: you do not want to have any popcorn noise.

reason:
Popcorn noise is issued by impurities in the crystal structure.
https://e2e.ti.com/cfs-file/__key/telligent-evolution-components-attachments/00-14-01-00-00-80-75-78/Popcorn-Noise.pdf

The buried zener was invented to avoid impurities near the zener junction leading to less noise and more long term stability.
See Appendix A:
https://www.analog.com/media/en/technical-documentation/application-notes/an82f.pdf

So any device with excessive popcorn noise is a defective device.

With best regards

Andreas

[Kleinstein]

Popcorn noise needs some electronic (or maybe a dislocation ?) quatum state that has a large effect on the result. This could be an impurity (or maybe even vacancy) at a sensitive point, but it could as well be a surface state or isolated state in the oxide layer.
If the popcorn noise is with just 1 defect state, this could well be rather stable. If it moves the popcorn noise would change over time.

The LM399 and LM1399 don't have the zener ref directly at the output, but more like a shunt regulator. So the question of the output stability and sensitivity is more like comparable to a voltage regulator. Some LDOs like capacitance with ESR. If they have the capacitance with ESR, they can that also tolerate additional small capacitance without much ESR. The point is avoiding the near 90 deg phase angle for the load impedance in a certain frequency range.

So chances are high the LM1399 would also be OK with the 22 µF tantalum cap and 100 nF MLCC in parallel.
It is natural that with more capacitance the series resistance can be a bit smaller.

From the impedance curve in the LM1399 datasheet it looks still underdamped with 5 Ohms and 1 µF. So chances are a bit more than 1 µF would be good, espeically if the 1 µF is a MLCC with reduced capacitance due to the DC bias. So I would plan with 2 parallel foot prints for capacitor, just in case.

[branadic]

Got some of these puppies too.

-branadic-

[miro123]

Me too. They are from the same batch 2113.
I wonder why there is a 9 months gap between production and shipment to the customers.

[Kleinstein]

Me too. They are from the same batch 2113.
I wonder why there is a 9 months gap between production and shipment to the customers.

This could be one of the early batches and the data from dirft test may not have been there to decide if the chips are any good. The date could be the date of the wafer production - mounting to the case may have happend later.

[maat]

The game is afoot. I have got the next batch of LM399s and the two ADR1399 in the burnin test setup.

[maat]

I was asked by Andreas  about the scanner card. The card is a replacement for the 2000-SCAN card for the Keithley 200x and DMM6500 series. The complete design files can be found over on Github: https://github.com/PatrickBaus/SCAN2000. The cable used is a Phoenix Contact 2926674 Dsub-50 breakout cable (https://www.mouser.de/ProductDetail/651-2926674).

It is based on the designs by fellow forum members cozdaz (https://www.eevblog.com/forum/projects/20-channel-diy-scanner-card-for-keithley-dmms-and-daqs/) and voltsandjolts (https://www.eevblog.com/forum/circuit-studio/example-project-20-channel-solid-state-scan-card-for-k2000-dmm/). The source code is inspired by George Christidis (https://github.com/macgeorge/SCAN2000STM32).

I did a redesign, because I wanted to use an STM32 MCU, as I use them on a regular basis at uni, so I do have all the SDKs ready and installed. Another thing was, that I wanted to replace some of the components to simplify sourcing them. Also I did not like the mechanical construction, because there was too much wear and tear on the guide rails in the DMMs. So I changed that as well.
The opto relays used are Toshiba TLP3558A (https://toshiba.semicon-storage.com/info/docget.jsp?did=60325&prodName=TLP3558A). These, I believe, are a very good compromise and can replace the original 2000-SCAN in almost all aspects.

The design is still a bit of work in progress. I do want to update a few final things:

• Test it in a K2001 (our neighbouring) group has got one, I believe
• Update the silkscreen to show the channels
• Add a Python example to scan the DMM

I guess I will get all of that done by the end of the week.

Edit: I do still have a couple of PCBs left from my order. So if people are interested, I guess we can work something out.

[daqq]

Found this in my email newsletter. Link is to the normal non-SMD part: https://www.analog.com/en/products/adr1399.html?ADICID=EMAL_WW_P328165_MIX-NPI-PN_996&deliveryName=DM21110

[branadic]

Must be either a marketing gag or a marketing flaw.

Pin-compatible LM399 replacement with improved performance"

Didn't know LM399 was available in a ceramic SMD package.

Edit: Seems like they are serious on that, wow.
https://www.analog.com/media/en/Other/Support/Customer-Service/ADI-Export-and-Import-Classifications.pdf

-branadic-

[Noopy]

A long time ago I have taken some pictures of the LM399 and the MAC199 (https://www.eevblog.com/forum/projects/lm399-die-analysis/msg2875790/#msg2875790) and tried to analyze the circuit. Now that I have a ADR1399 I first have to do an update on the LM399 and the MAC199. Putting the update in this topic here seems to be sensible.










Well you know the package.




Quite a big die for the small TO-46 package. (Yes, that´s an old picture.  )




This picture is a little better than the old one. 199I stands for LM199, the variant with a higher temperature rating.






At the lower edge there are the revisions of six masks. One more revision marking is near the bondpad of pin 1. The arrow highlights bondpad 1.




The LM399 is a shunt regulator. The power part (blue) is built with a sziklai pair. The RC prevents oscillations. The 50R (green) is the emitter resistor for the sziklai pair. It is protected by Q10. If there is to much current flowing through the resistor the transistor opens a bypass.

Q3 (dark green) is the reference, the buried zener. The current necessary for the zener is determined by the 2k resistor.

The red part drives the sziklai pair. If the voltage across the terminals of the LM399 increases, the voltage across the 2k resistor is increasing, increasing the current through Q13, increasing the current through the sziklai pair and finally reducing the voltage across the terminals of the LM399. The RC prevents oscillations.

The pink part is a feedback biasing Q13. A voltage higher than 6,9V at the LM399 terminals gives you more current flow through Q13 and more current through Q16 too. The current mirror Q14/Q15 feeds the current into the node Q12/Q13 working against Q13 sinking current to lower the voltage across the LM399. This is probably for biasing Q13 into an ideal operating point. But it´s interesting that the bias increases with increasing deviation of the voltage across the LM399. 




The shunt regulator is in the upper part of the die. In addition to the parts in the schematic you can find the diode between heater and regulator ground (green) and some more parts at the upper edge of the die (red).
The 10k at the base of Q13 can be tuned.




A nice starpoint supply.  The shunt regulator is connected to red/blue. The zener is supplied by yellow/green and the rest of the circuit is connected to pink/cyan.




Here you can see the additional circuit. T17 is hard to recognize. The right contact of the resistor R14 connects to the n-doped well too and acts as a collector for T17.




Tesla has copied the LM399 (MAC199). In the schematic of the MAC199 you can find the additional circuit (red). It looks like it is an additional current sink for the zener. T17 does some current limiting.
I have no idea why they integrated this circuit. 




The buried zener diode…




The transistor Q16 is interesting. It seems it has a big and a small collector contact, four base contacts (two of them connected) and one emitter contact. A lot of options…




The Darlington pair Q1/Q2 (blue) is the heater. The green circuit is an overcurrent limiter.

The dark green circuit generates a reference current for the two current mirrors (red). Q7 biases the driver circuit. Q4 (pink) is the temperature sensor. With a higher temperature Vbe drops drawing more current of Q7 and reducing the current trough the Darlington stage.

Q5 supplies D1 with a constant current. The orange circuit supplies a voltage at start-up. Q8 isolates the start-up circuit as soon as the reference circuit is active.




At the lower edge there is the big transistor Q1 which consists of 21 transistors. It has to dissipate up to 5,5W. The 4R2 resistor of the current limiting circuit can be adjusted.

In the heater circuit you can find the diode ZD2 above the transistor Q2. The MAC199 schematic shows this diode. It lowers the potential of the transistor Q2 so it´s easier to drive it.

The temperature sensor Q4 is near the reference zener. The voltage divider 11k2/1k allows a lot of different connections which moves the desired temperature.

The combination Q8/Q9/D2 is integrated quite efficient. 




In the first place I guessed the die is placed on an additional layer that protects the reference circuit from mechanical stress. Today I assume the rough edge is due to breaking of the wafer after sawing the upper part.


https://www.richis-lab.de/REF02.htm

 

[Noopy]

Here comes the update for the MAC199.
Tesla has built the MAC199, the MAB399 and the MAE299. These are just binned variants of the same reference which allow different ambient temperatures. The MAC199 is specified for a temperature range of -55°C up to +125°C.






The MAC199 uses the same package type as the LM399 but the case is a little higher because the package is a little higher.






Looks like the LM399. There are just some small differences.




Here you can see some structures that show the mask alignment. And there is the logo Tesla puts on all of its circuits.




In the upper left corner you can see eight mask revisions. In the LM399 we just saw seven masks. Some of the masks were modified four times.




The buried zener looks quite the same as the buried zener in the LM399.






The circuit of the LM399 and the MAC199 are quite similar. As we have seen the red circuit is integrated in the LM399 too.
You can find the resistor R16 neither in the MAC199 nor in the LM399. It´s probably highly integrated in the dense area in the upper right corner, perhaps in the LM399 too.




The reference circuit looks pretty like the LM399.




But hey, there is a connection missing between T16 (yellow) and T15 (red). That´s strange...

By the way: T16 looks interesting. There are five base connections and four emitter connections.






Without the connection a lot of the circuit is dead. But it would probably still act like a reference. Probably a worse reference.




Looking closer you can spot some edges caused by the buried collector. It looks like the buried collector of T16 and T15 are connected. 




The MAC199 heater schematic is more complete than the schematic of the LM399. Here we have the zener in the collector of the transistor T2. The emitter resistors of T1 are represented by R2.




The heater part on the die of the MAC199, nothing special…




The side of the die has the same structure as the side of the LM399 die. It is probably sawn a bit and then broken out of the wafer too.


https://www.richis-lab.de/REF02a.htm

 

...on my side it looks like the forum shows the old die overview and the mask revision pictures.  The new and better one are on my website. Perhaps you have to clear your cache.

[magic]

I always assumed that those trenches indicate location of holes where isolation dopant had been applied.



So there is no isolation diffusion between Q16, Q15 and Q14 on both versions of the chip and hence Q16 collector is connected with PNP bases through the whole thickness of the epitaxial layer.
The green/mustard border between transistors looks identical as NPN bases, suggesting it's surface processing. Maybe an effort to strengthen isolation diffusions, applied more or less automatically (and mindlessly) at some distance from active areas of all transistors.

Regarding T17, T18 - it's a current mirror. Of sorts. T17 sinks T14 collector current through R14. T18 base voltage is simply T17 base voltage, minus whatever is R14 voltage drop. Then there is some further resistance in T18 emitter.
It obviously provides additional bias to the zener and I can guess it's supposed to have some particular kind of variation with temperature. Similar tricks are found bandgap references.

[Noopy]

I always assumed that those trenches indicate location of holes where isolation dopant had been applied.

You are probably right. 

So there is no isolation diffusion between Q16, Q15 and Q14 on both versions of the chip and hence Q16 collector is connected with PNP bases through the whole thickness of the epitaxial layer.

I agree with you.
But it would probably be a relevant resistance. With the buried collector you get a low resistance path.

The green/mustard border between transistors looks identical as NPN bases, suggesting it's surface processing. Maybe an effort to strengthen isolation diffusions, applied more or less automatically (and mindlessly) at some distance from active areas of all transistors.

Sounds reasonable. 

Regarding T17, T18 - it's a current mirror. Of sorts. T17 sinks T14 collector current through R14. T18 base voltage is simply T17 base voltage, minus whatever is R14 voltage drop. Then there is some further resistance in T18 emitter.
It obviously provides additional bias to the zener and I can guess it's supposed to have some particular kind of variation with temperature. Similar tricks are found bandgap references.

T17/T18 is a current mirror? Sound strange...
As long as the base current of T18 is low enough and the resistor R14 is small enough T17 shouldn´t conduct anything. R14 looks like round about 3k. 100µA should be no problem.
Yeah, it´s probably some kind of compensation for something. Temperature should be constant but of course you can´t guarantee it´s always exactly the same value.

[Noopy]

Wait a minute! Now I see your point!
Since the supply is a current source T17/T18 behave like some kind of current source! You are right! 
Thanks for your input!

[magic]

The biasing of Q13 is another old trick. Each of those mirrors has an emitter resistor and more active area in the output transistor than in the input.

At low currents, more active area means more current for the same Vbe so the mirror's output is more than the input.
At high currents, the resistor drops serious voltage, Vbe of the output transistor decreases and its current is less than the input.
Equality is achieved at a particular current which causes output emitter resistor voltage to be the logarithm of the ratio of active areas, and the base of the logarithm depends on temperature.

In LM199:
Low voltage: Ic(Q13) < Ic(Q16) and Ic(Q14) > Ic(Q16) → output stage is pulled up (disabled)
High voltage: Ic(Q13) > Ic(Q16) and Ic(Q14) < Ic(Q16) → output stage is pulled down (enabled)

Observe that both Q13 and Q16 have a lot of potential emitters but only one is actually connected. It looks like some serious tweaking took place on the design stage.

Example sim attached. I can change transistor types and it behaves more or less the same.

[RikV]

Is there any information on the ADR1399 in ceramic HLS8 package? what is the exact reference number? Datasheet? specifications?