ADR1001 - Ovenized Voltage Reference System

[sahko123]

Yeah it would have happily lived at 125c since that is one of the potential settings of the adr1001. Though i wouldnt feed it from a divider unless you are using a trimmer. At that point i would simply use a single resistor

[iMo]

OK, this is the "first" myADR1001 measurement ran over night in an insulated box. The external TEMP divider is disconnected, thus working with the stock TEMP setting (70C based on the simulation). Blue is the temperature inside the box.
Anyhow, it looks like my 23y old LM399 works pretty well 

[Villain]

Did anyone create a PCB for ADR1001 yet? Would love to build a board, my PCB design capabilities are almost 0 though.

[sahko123]

at this point its mostly just making sure that the thermals are taken care of properly along with bypassing the IC.

otherwise the pcb design can be very simple. It only gets complicated in the case of the LTZ/ADR1000 where every sniff and fart needs to be accounted for.

So effectively the point of the ADR1001 is to make the pcb as simple an compact as physically possible

[iMo]

There is the question how to make the pcb.. People here will tell you a FR4 or similar "works" based on humidity, temp, etc., thus creating mechanical stress..
That would be the same discussion as with the ADR1399 in smd..
Perhaps a thin flexible pcb?

[Villain]

I think even having "best effort" FR4 layout by someone would be amazing, even if its just to gain data and experience with ADR1001 chip.
Its still a lot more professional than soldering legs to ADR1001 and make due with euro board.

[iMo]

Yeah it would have happily lived at 125c since that is one of the potential settings of the adr1001. Though i wouldnt feed it from a divider unless you are using a trimmer. At that point i would simply use a single resistor

OK, so do you mean to wire the resistor based on where you want to set the temperature (we would probably see that in the DS  ) - see below for example.. ?

[sahko123]

Yes this is how it should be done. Doing it with a divider ends up being redundant and just wastes the space for another resistor. Plus the datasheet table references it this way for the corresponding set temps

[CorporateReference]

Has anyone been able to verify the ADR1001's noise? The data sheet says 0.6μV p-p. That's 0.3μV better than the ADR1000 specs 0.9μV p-p! 

[iMo]

I removed the external TEMP divider, left the jumper X1. It could be used for a faster burn-in at higher temperature (connecting TSET via a resistor to GND, provided ADI recommends that).
Also I added an 0.22ohm resistor to the green ~110ohm ISET one, the output voltage dropped by aprox 60uV.
I also created my diy 111ohm ww resistor, an over night measurement showed an 1ppm relaxation, thus such stuff needs special cure and expertise.
At this moment my home 34401A (calibration doublechecked by Jaromir's great LTZ calibrator) reads 10.000111V so I let it be for a while running and let us all wait for the official ADR1001 release including the datasheet v1.0. !!

[iMo]

Below my today's DIY 110.3ohm WW resistor wound with a 14.9ohm/100mm manganine wire.
Fine tuned by slowly cutting millimeters off, such my meter reads 9.999.998V (the board in the insulation box, temp aprox 30C)
The wire has not been cured yet, just baked for a couple of minutes at 60mA (wire below 50C).
Also ADR1001 will go lower (??), as the experience here with the ADR1000 shows, thus I will try again with the resistor to get it over 10 a little bit..
PS: hopefully I will not be listening short wave broadcasting at the 10V with such a nice loop antenna 
I will try it next time bifillar, or I will change wire direction while in the middle..

PPS: FYI - below a simulation of the fine tuning sensitivity (in uV/ohm) with 3 possible options: RA, RB, RC resistors for 10V output.
All are with negative slope, a pity.

[Villain]

I removed the external TEMP divider, left the jumper X1. It could be used for a faster burn-in at higher temperature (connecting TSET via a resistor to GND, provided ADI recommends that).
Also I added an 0.22ohm resistor to the green ~110ohm ISET one, the output voltage dropped by aprox 60uV.
I also created my diy 111ohm ww resistor, an over night measurement showed an 1ppm relaxation, thus such stuff needs special cure and expertise.
At this moment my home 34401A (calibration doublechecked by Jaromir's great LTZ calibrator) reads 10.000111V so I let it be for a while running and let us all wait for the official ADR1001 release including the datasheet v1.0. !!

Release was postponed unfortunately

[sahko123]

honestly if its released later and is better/more stable than if it were released today than i dont mind the delay. but at this point i think this is the third or fourth delay lmao 

[Villain]

honestly if its released later and is better/more stable than if it were released today than i dont mind the delay. but at this point i think this is the third or fourth delay lmao 

fully agree.. lets see if june is the month

[iMo]

The output voltage went up by some +1ppm a day after the soldering the manganine ISET resistor in.
Out of curiosity I made then a simple TC sweep to get an idea on the board's TC.
Board in the insulation box, the temp sensors inside the box off the chip.
See the results below.
Disclaimer: this is not the metrology grade measurement nor the dmm used is, and the sample has not been officially released yet.

[sahko123]

Do you have this at home or in an office?

[iMo]

FYI - see below the output voltage (10V) vs. input voltage dependence for myADR1001 (on free air, aprox 22C ambient).
The 78L15 has been removed and I will try with 78L12 instead. It seems the ADR1001 starts to operate around 11.5V Vin (configured for 10V output).
"Power_Good" output has not been monitored yet.

PS: done, now with 78L12, stable, and with 10.000.030V output (in the insulated box at 29.2C)..

PPS: when loading the output with 100k the voltage drops down by 20ppm. Is Vin=12V enough for the output buffer then?

[iMo]

My mod for the ADR1002 - INV0 allows a) for output voltage fine tuning with a positive slope, b) easier output buffering (an external opamp or transistor "inside the control  loop")..
 

[iMo]

..
PPS: when loading the output with 100k the voltage drops down by 20ppm. Is Vin=12V enough for the output buffer then?

Removed the 78L12 and tried with 12-16V.
With Vin=16V the 100k load resistor (wired directly at the board's posts) drops the output voltage down by 17ppm (>10Gohm dmm set).
Hmm..

[Kleinstein]

Some 20 /17 ppm of drop from loading with 100 K suggest an output resistance of soem 1.7 to 2 ohm.

It depends on the internals if 12 V supply is enough to drive a 10 V output, but 16 V should definitely be enough. With a higher valtage there can be a thermal problem: more load current gives more power loss from the driver and this can disturb the thermal balance of the chip.  Even with the extra amplifier the ADR1001 is not really suitable to directly drive an external / variable load.

[mawyatt]

One could use a simple NPN Emitter Follower (2N3904) "inside the loop" if the supply is high enough to support an output of 10 volts, or a PNP Emitter Follower (2N3906) if the supply is lower. Either should produce an output impedance well below 1 ohm if the internal op amp has reasonable open-loop gain.

Best,

[iMo]

One could use a simple NPN Emitter Follower (2N3904) "inside the loop" if the supply is high enough to support an output of 10 volts, or a PNP Emitter Follower (2N3906) if the supply is lower. Either should produce an output impedance well below 1 ohm if the internal op amp has reasonable open-loop gain.

Best,

Yep, that would work with the ADR1002 (see above) but not with 1001 - there is the hot side of the divider wired inside the chip to the buffer's output.
How would you wire the npn inside the loop with the 1001?

[magic]

I imagine it could still work if you forgo gain and go for 5V output.

But 0.2mV output step under 100kΩ loading? From an opamp? At DC?
Are you sure everything is star grounded and Kelvin sensed properly?

I recall playing with a breadborded circuit which displayed negative PSRR.
I take it as evidence that given bad enough grounding, everything is possible.

[iMo]

The wiring has been made exactly as in the schematics above, therefore I draw it in that messy way.
I grounded the internal output buffer at the "power_gnd" star.
PS: there is none wire with more than 15mOhm used on the board, so the 170uV delta at 100uA is less probable..

[magic]

Okay, so you connect a DVM across BUF_INP and BUF_S, and you see the offset voltage jumping 0.2mV 0.1mV due to 0.1mA output loading?

BTW, beware that DVM capacitance on input pins could upset an opamp and cause it to oscillate. Series resistance may help.
Actually, output capacitance could do it too, did you check?

I gather it's a preproduction sample, do you have any datasheet / application info or just working completely in the blind?