New TI REF54EVM Evaluation Module Leaked

[miro123]

Can you dry the PDIP package and then coat it in a marine waterproof epoxy to get the same benefit ?

I think that you are referring to conformal coating. Humiseal  is leader in this area. I evaluated different conformal coating and potting in the past. My conclusion match the findings from AD. Conformal coating only delays reaction to humidity variance. Any material absorb water, some material dry faster. Adding conformal coating makes you mathematical model or resistor/voltage reference more complex as it was.
https://eprintspublications.npl.co.uk/3870/1/DEPC_MPR60.pdf
https://www.analog.com/en/analog-dialogue/articles/does-my-voltage-reference-design-hold-water.html
https://chasecorp.com/humiseal1/wp-content/uploads/sites/12/2018/10/1B51-TDS.pdf

[miro123]

Interesting, looking at the application note for the datasheet, they want at least a 1uF cap on the output ('must be connected') but warn against the cheapest route, X7R MLCC.

Perhaps also a second source is profitable in a niche market like this?

Having another OEM for a good part is never a bad thing

With the risk that I offend AD fanboys I will make the following statement.
 - @ 9-th of December 2023 ADR4525D - only exist on datasheets and Youtube intro videos
 - ADR4525C grade is available on insane price of 21..22Euro -23..24USD
Please correct me if I'm wrong
I'm lucky guy. I have chosen Ref7025QFHT. It is more down to earth device - broadly available and reasonable price of 12 Euro for single pcs. 
My point is, yes the second source is always good to have.

[Kosmic]

Can you dry the PDIP package and then coat it in a marine waterproof epoxy to get the same benefit ?

I think that you are referring to conformal coating. Humiseal  is leader in this area. I evaluated different conformal coating and potting in the past. My conclusion match the findings from AD. Conformal coating only delays reaction to humidity variance. Any material absorb water, some material dry faster. Adding conformal coating makes you mathematical model or resistor/voltage reference more complex as it was.
https://eprintspublications.npl.co.uk/3870/1/DEPC_MPR60.pdf
https://www.analog.com/en/analog-dialogue/articles/does-my-voltage-reference-design-hold-water.html
https://chasecorp.com/humiseal1/wp-content/uploads/sites/12/2018/10/1B51-TDS.pdf

I wonder if potting with a really tick layer could give better results ? From AD tests, 1B73 applied on the board seem useless.

[Kleinstein]

A thick layer of potting material or similar plastics would add additional possible stress from curing / thermal expansion. It would make things slower, but also more compicated with more processes to add drift processes and maybe slower setttling. Unless really water repellant I am afraid it would only make things worse.

There is still quite some long term drift for both the ref54xx and ref70xx. So I don't see them a replacement for a hermetic reference. The nice point is gettting away with low power and having a reference driver included. I already see little sense in using the ref54xx together with an external reference buffer. The main use for the ref54xx would be more less demanding ADCs / DACs that can woork with the internal driver directly. If the ADC needs a lower impedance, the ref70xx may be the better choice.

[iMo]

Keep away from plastic/epoxy packages when targeting something more demanding.
The only suitable packages are the metal hermetic one, then ceramic one (when not soldered directly onto epoxy pcb). There is not a sealant available which would make an epoxy package hermetic..

[miro123]

There is still quite some long term drift for both the ref54xx and ref70xx. So I don't see them a replacement for a hermetic reference.

Just for clarification, not all ADR45xx are in ceramic package and not all REF70xx are plastic. In case of ADR4525 only D grade is ceramic package - unfortunately only awailable on datasheets and AD advertisements. C grade in plastic is available for 22Euro/pcs
In case of REF7025 in ceramic package is available in most shops ~12Euro/pcs -  https://nl.mouser.com/ProductDetail/Texas-Instruments/REF7025QFKHT?qs=TuK3vfAjtkUpFxL4w6H61A%3D%3D

[miro123]

Hopefully I will no  hijack the threat with my questions.
 1. How semiconductor manufacture measure the output voltage thermal hysteresis
   - Temperature ramp-up rate - e.g. from 25->70C with ram rate of 10mK/min
   - time to stay at temperature - e.g. 10 min, 24H or many days stay @70C
   - ramp down time
  - time to stabilize at 25C before take measurements.
2. How the semiconductor manufacture measure the long term drift - The list of parameters is enormous.
3. Is there any ISO standard for testing 1 & 2

[floobydust]

Long-Term Drift in Voltage References TI App. Note  SBAA436 they use an oil bath to measure LTD, so it appears moisture is not included as a factor and I would say misleading for plastic-package parts.

REF7025 LCC package same price point as REF54 SOIC-8.  I guess the $ is for the lower quiescent current.

[Andreas]

Hello,

the sad truth is that you often cannot compare these values.
In some older data sheets hysteresis is given for 25 deg C +/- 25 deg. In others over the full commercial or industrial range.
As a rule of thumb the drift is proportional to the square of the temperature excursion.

Often hysteresis and ageing drift are only given for the best package (metal can) and the information is not updated if this package is no longer produced ...

Some specs for the hysteresis are given for the 2nd temperature cycle.
Or for the 2nd 1000 hrs regarding ageing.

So I never trust the datasheet values.

with best regards

Andreas

[eplpwr]

In my earlier post, I should have included the link to Analog Dialogue Vol 53 number 3. Here it is:

https://www.analog.com/media/en/analog-dialogue/volume-53/number-3/volume53-number3.pdf

There are no pictures of the board(s) they used, but they tried different HumiSeal coatings for the plastic Vrefs. In summary, the coating didn't do much.

BTW, somewhere in my stash I have 10pcs ADR4550DEZ, so they do exist. I remember putting in a back order with Mouser DigiKey, and receiving the chips long after I had forgotten about my order.  [Shipped 4th of june 2021]

Edit: Wrong distributor specified.

Edit2: DigiKey order history says I ordered (and they shipped) 2 pcs ADR4525DEZ on 2021-11-15, so those exists as well. Maybe I need some better inventory management skills ...

[floobydust]

I wonder if they are collectibles    Mouser does not list the ADR45xxD. Digi-Key shows no stock, no price, no lead time - request quotation only.
There were delays closing the Milpitas wafer fab(s)/hermetic packaging, it might have happened end 2021/beginning 2022 and you got that stock? But today it appears the parts are unobtainium.

Why is the new REF54 not offered in the LCC-8 package?

[Kleinstein]

Why is the new REF54 not offered in the LCC-8 package?

That is a good question. Still with the ref70xx the performance in the LCC-8 package is still not that much better than in a plastic case as one may hope for.
If power is not a big issue the ref70xx may be the alternative that is available in LCC-8.

[floobydust]

It must be marketing specmanship - advertise the Holy Grail of low TC, yet moisture and flex stress of the plastic package undermine the overall performance and let's all be in denial and not mention it in app notes or datasheets.

I found this on LCC CTE which I was wondering about, did not compare to old friend TO-46 package rolled out in 1962, it's over 60 years old.

[Andreas]

Hmm,

https://cleanroom.byu.edu/cte_materials

Kovar (the bottom of a TO-package) is 5.9
Silicon is 2.6
The big advantage of a TO-package is that the PCB stress is decoupled by the wires.

with best regards

Andreas

[floobydust]

I was thinking of thermal properties between the PCB and LCC, and any advantages of the LCC package beyond the hermetic seal.

LCC ceramic material I find Kyocera A440 CTE 7.1 and thermal conductivity 14.0 W/mK, Young's Modulus 310.
So it is quite rigid and an excellent conductor of heat. CTE is greater than Kovar by a little. FR-4 CTE is 13-17 and I have no idea how much stress is on the IC package after reflow, if it's significant. Ceramic is very stiff.

A reference with on-die heater i.e. ADR1399KEZ "The heater power for the LCC version is about 3× to 4× greater than the TO-46 version." They could probably use the LTZ1000A die attach technology if they weren't lazy.

So it seems a REF54 in LCC would only benefit from the hermetic seal against moisture, and see much less package flex and die stress from that?
I remember a product SOIC-8 op-amps that had huge offset shifts when the PCB was flexed, it was a nightmare in production to calibrate.