The LTFLU (aka SZA263) reference zener diode circuit

[janaf]

Now I need some good advise 

What / how to map the LTFLU transistor to get a basis for making a circuit around it. I Never did any transistor characterizing before.

I have two channels SMU that each can measure in constant current or constant voltage mode, can sweep either. (Voltage and current limits available independently as well). The two SMUs can be synced. Both voltage and current are measured independently for both channels.

For now, I think I will measure

• room temperature
• static data, no dynamics / frequency dependency

Later

• combine with the diode
• measurements at other temperatures
• several devises

The number of measurements must be held at a manageable number.

First measurements could be:

• Constant CE voltage (like 1V, 2V, 5V), sweeping BE voltage (up to 0.1mA?)
• Constant BE current (like 10uA, 100uA, 1mA, 10mA?), sweeping CE voltage
• Constant BE voltage (like 0.4, 0.45, 0.5, 0.55, 0.6V), sweeping CE current

Some results will be redundant but that's OK for double-checking.

Once a clear measurement matrix is established, I could automate the whole sequence.....

Feedback appreciated!

[janaf]

Here are some more measurents made on the LTFLU. This time on the transistor.
They are still just at room temperature as I'm waiting for some parts to build a small temperature chamber.

[janaf]

I just updated the file with the previous post because one of the figure legends was screwed up.

Anyway, I'd appreciate any feedback of what kind of measurements / plots would be useful for making a circuit around the LTFLU. 

[Jim Narem]

In your LTFLU_Measurements_201.pdf file, page 3, you show what looks like
a curve trace of the NPN transistor in the reference, except that the base-emitter
steps are in volts.  Shouldn't that be in amps (probably microamps)?

I'm wondering since I'm repairing a Fluke 5440A which uses 2 SZA263s in it's
ovenized voltage reference and one of them is acting up.  Using a Tek 576,
I can see the zener just fine but the transistor seems a bit odd.  Without
the spec sheet, it's hard to know what to look for and the datasheet for the LTZ1000
has some scary warnings that imply that its on-die transistor isn't very robust.

......jim (narem at narem dot com)

[richiem]

Fluke Motorola ref-amp were also used in the 8800A and 8810A meters, predecessors to the 8840/42 -- these are currently very cheap on ebay if anyone wants to get the Motorola version of the ref-amp with the selected WW zero-TC current-setting resistor. Oh and they are the reference in the Fluke 510A AC standards, too. Fluke really used a lot of these in all kinds of gear, including the 8502/5/6 DMMs, which I think maybe all had the LT versions...

[dr.diesel]

Anyone mind if I necro this thread?

Any thoughts on why Keithley decided on the LTFLU over the LTZ on the new DMM7510?

[ltz2000]

Any thoughts on why Keithley decided on the LTFLU over the LTZ on the new DMM7510?

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

[dr.diesel]

I'm assuming you mean it's simply cheaper, I'm guessing more too it than that.

Perhaps lower noise?

[plesa]

I'm assuming you mean it's simply cheaper, I'm guessing more too it than that.

Perhaps lower noise?

I think that main reason is implementation cost. Fluke/Danaher they have lot of experience with LTFLU and thats why they used it also in Keithley instead of LTZ1000.

[dr.diesel]

Well perhaps. 

Isn't everything that used the LTFLU, including the 8508A discontinued, why was LT still making it vs obsolescence?  Or did Keithley find a pallet of these in Fluke's basement when the thought of the 7510 came up?   

I presume LT was either still making them, or easy for them to do so, otherwise the LTZ would have been cheaper.  Though I can't find a new price for the LTFLU anywhere.

Too bad for the secrecy, I guess we're not likely to find out more.

[Dr. Frank]

Well perhaps. 

Isn't everything that used the LTFLU, including the 8508A discontinued, why was LT still making it vs obsolescence?  Or did Keithley find a pallet of these in Fluke's basement when the thought of the 7510 came up?   

I presume LT was either still making them, or easy for them to do so, otherwise the LTZ would have been cheaper.  Though I can't find a new price for the LTFLU anywhere.

Too bad for the secrecy, I guess we're not likely to find out more.

Why do you think the 8508A is discontinued? It is still available on Flukes site, no hint of obsolescence.
The LTFLU is also used in all actual Fluke calibrators and references, like 5730, 732B, maybe very probably also in the 5790B, which are also not discontinued.

The LTFLU is a proprietary part, manufactured by Linear Technology exclusively for Fluke.
So no wonder you won't find a price, and can't buy it from them.
There's also no reason to believe that LT stops producing the LTFLU, like the LTZ1000, which is also still available, despite the limited sales volume.

Fluke for sure follows the policy to focus on the reference amplifier topology based on the SZA263/LTFLU type.

They also acquired Datron, including the 7001 reference (based on LTZ1000), and a few years later terminated this instrument.
That at first eliminated a competitor, but also saved cost, as their 732B was as good as the 7001, and they wouldn't have to maintain two different systems any more.

That includes all the validation / verification / monitoring for the references, where now they have to maintain one process and production line only.

Frank

[dr.diesel]

Why do you think the 8508A is discontinued? It is still available on Flukes site, no hint of obsolescence.

A reference here:

https://www.eevblog.com/forum/testgear/its-no-fluke/msg14285/#msg14285

And a search of a couple T&M sites also show it discontinued.  Perhaps you can still get it from Fluke directly.

No worries though, maybe rolling off the line as we speak!   

[Dr. Frank]

Rumors only, obviously..and 5 years old..

If you search for really terminated products on Flukes site, you will get an explicit note, that they are terminated.


Very funny, as I'm reading your response, this ad just appeared on the bottom of the forum: 
So, let's get a quote for it..

[Dr. Frank]

How a query for the 7001 looks like

[dr.diesel]

Very interesting, thanks DM.   

[branadic]

But, that would be really expensive, and with the market as slow as it is for these kinds of parts, who is going to pay for the design work?

Well, let's suggest LT that they advertise a PhD or master thesis for such a redesign with all ideas given by the forum verified by the student

[Macbeth]

But, that would be really expensive, and with the market as slow as it is for these kinds of parts, who is going to pay for the design work?

Well, let's suggest LT that they advertise a PhD or master thesis for such a redesign with all ideas given by the forum verified by the student

That's a good idea. Because their China counterparts can threaten their cushy market with the guys at bbs.38hot.net 

[plesa]

The Zener in the LTFLU has about 4X the area that the LTZ's Zener has, so they can get away with the higher currents without reducing reliability or increasing time-drift [due to the interconnects changing properties].

Hi Ken,

Thanks for sharing!! You mentioned in the LTZ1000 thread reply from Bob Dobkin and he said that "You can safely bias the LTZ1000(A) with 20mA." So It looks like we can increase current also with LTZ1000.But I do not know if this can ruin long term drift and etc.

Let me know if you know cheap source of LTFU (including not working). Die image can follow

[feedback.loop]

By the way, I recently repaired Fluke 341A calibrator, which uses SZA263 reference. Here is the topic: https://www.eevblog.com/forum/metrology/fluke-341a-dc-voltage-calibrator/
One can see the reference in the video at 16:07

Here is the schematic from Fluke web site: http://assets.fluke.com/manuals/341A_343imeng0000.pdf

[zlymex]

.....
Let me know if you know cheap source of LTFU (including not working). Die image can follow

[kriwoel]

.....Let me know if you know cheap source of LTFU (including not working). Die image can follow
[/quote]

Shenzhen...?   
 
http://www.alibaba.com/product-detail/-electronic-parts-and-components-Transistor_60305153923.html

[BU508A]

Hi plesa,

Let me know if you know cheap source of LTFU (including not working). Die image can follow

I've bought here today 5 pieces of LTFLU-1ACH. Price per piece: U$ 25.-- plus shipping plus Paypal fee.
http://goo.gl/aD205s  (Link points to de.aliexpress.com)

Cheers,

BU508A

This is a photo I got from Barry (seller at this webshop)

[Andreas]

This is a photo I got from Barry (seller at this webshop)

Hello,

for me they look like fakes.
The printing orientation does not comply with the original ones.
(the pin 1 marker of the package in direction of the LT logo).

With best regards

Andreas

[plesa]

This is a photo I got from Barry (seller at this webshop)

Hello,

for me they look like fakes.
The printing orientation does not comply with the original ones.
(the pin 1 marker of the package in direction of the LT logo).

With best regards

Andreas

I also suspect that these are fake ones.

[Macbeth]

For sure they are fake. All the same manufactured date? These could only be obtained as salvage surely?

Also, aren't the LTFLU normally matched with individually laser cut precision resistors as a set?