ADR1399 reference

[bobAk]

Hello. Has anyone tried to connect adr1399 in series? Like lm399. It’s more interesting how it behaves, since changes in the control loop of the shunt part in comparison with lm399 led to the need to install ~1 µF 5 ohms. In theory, there should be no problems, due to low impedance. Requires ~14 volts with low noise.

[misterpulcri]

Hello,

Apologies, my question is pretty basic but I see a lot of expertise here and no other suitable ADR1366 forum. Happy to be redirected somewhere more appropriate if I am in the wrong place.

I have attempted to build a basic voltage reference using a ADR1399K with +12v supply, 1K3 shunt for 3mA at 12V, 5R1 and 1uF as per the datasheet. Have built this three times now on breadboard and stripboard. Each iteration produces 6.920V instead of the expected 7.05V. At each power on my DVM reads 6.925 and within a few seconds this decreases and stabilises at 6.920V. I have verified that I have just over 3mA flowing through the shunt. Have checked with 2 other hand held DVMs and get the result as my bench DVM. Have checked DVMs against a fairly accurate voltage source

Am I missing something or is my ADR1399 faulty?

Thanks

Sean

[Kleinstein]

There is quite some variations between different units of LM399 and ADR1399. The ref. voltage can vary quite a bit. The specs are 6.75 to 7.3 V, though the extreme values are rare. 7.05 V is just a typical value. So the 6.92 V are perfectly reasonable.

[misterpulcri]

Ah, OK thanks. I can at least stop pulling my hair out.

[Andreas]

At each power on my DVM reads 6.925 and within a few seconds this decreases and stabilises at 6.920V.

Hmm,

Are you Kelvin sensing the voltage at the zener or are you measuring the sum of the zener voltage and the voltage drop of the heater current on the ground connection?
But even without that it needs some time until steady state is reached.

with best regards

Andreas

[bastl_r]

Hi

What did you use to measure the reference voltage? It is advisable to measure it with a measuring device with an input voltage divider in the G-Ohm range. I once had an aha-experience on my Solartron 7066 when I wanted to check the reference voltage before the buffer. The standard 10MOhm of the 34401a was not enough and the voltage dropped a few 10µV...
Whether this also applies to the ADR1399 I cannot say at the moment.

Greetings bastl_r

Translated with DeepL.com (free version)

[misterpulcri]

Hi all and thanks for your replies. I should explain my objective and reason for constructing an ADR1399 based voltage reference. 

My "best" DMM is an ancient Fluke 8050A and I wanted to check the calibration of this device. I need to be able to measure down to 100s of uV which this meter will not do, but I wanted to ensure I was ballpark in the mV range.

I construct Eurorack synthesiser modules which use the 1V/octave system for voltage to pitch  i.e. note C0 = 0v, C1 - 1.0v etc. Each octave is divided into 12 semitones and each semitone is a 0.0833V increment.

Mouser sent a product announcement for the SMT version of the ADR1399 so I investigated and purchased the through hole version naively thinking that if I built the circuit in the datasheet adjusting my shunt value to ensure 3mA for the Zener, 7.05 volts would be present at the reference output and I could gain a degree of confidence in my meter calibration at least down to the mV range.

Before cominng here I did experiment with different shunt values to swing from <3mA up to 5mA and also varied my supply voltage etc and always seeing 6.920V.
I now know that my voltage reference build is fine and is accurate and stable at 6.920 instead of 7.050V 

Thanks again for taking the time to look at my naive newbie experiments, I will most likely purchase a new DMM that gets me into the uV range.

Thanks

Sean

[Kleinstein]

When the layout is right, the ADR1399 has a rather low output impedance (< 0.1 ohm) and should be OK even with a meter with 10 M input impedance.

The ADR1399 is however the totally wrong way to hope for an absolute value of the voltage. There is quite some tolerance in the voltage, but that value is quite stable.
There are other reference chips for a good accurate initial value (e.g. Ref102C or max6126A) : better accuracy, but not as stable.

[dazz1]

I could post the KiCad, Gerber and BOM file for the circuit I build if that fits your need. But they are pretty messy since that was my first design in KiCad.
I would need at least a few days to clean up the most important errors.

Hi
I like your design.  Simple single purpose, no unnecessary complexity.
If you haven't already, could you clean and post your files please?
Are there any changes or improvements you would make?