REF5010 question - Page 1
Forum section: electronics / general

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 26, 2020, 07:19:14 pm
content: In TI application report they stacked REF5010 in serial to create high voltage precision voltage reference:http://www.ti.com/lit/an/sbaa203/sbaa203.pdfIt was discovered that by connecting the Vin and Vout pins together, the REF50xx is converted to an ideal Zener diode without any negative side effects. This is technically a small violation of the datasheet but when they tested it... it worked. Why couldn't you do the same thing with multiple REF5010's instead in parallel? Wouldn't this spread out the drift and TC issues across multiple sources and average out many of the things we're always trying to reduce in a precision 10V voltage reference? In addition, wouldn't this allow larger loads to be applied to the reference? Maybe I'm thinking about this too simply but it would seem putting this on a PCB in a temp controlled container could produce a better reference than you could ever get with just one REF5010. Am I missing something? Can't you do basically the same thing with multiple LTZ refs in parallel? Reduce noise and average out drift?Regards,Bill

author: iMo
author_rank: Super Contributor
timestamp: February 26, 2020, 07:44:21 pm
content: Wiring N references in parallel is a standard approach. It will decrease the noise sqrt(N) times and it averages the output voltages as well.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 26, 2020, 07:48:26 pm
content: One can use multiple reference in parallel - however this requires additional resistors or a similar circuit to get the average. Just the chips in parallel will not work, as they are not perfectly identical and fighting each other. So one would not get the average, but more like the highest of lowest value.For the noise averaging works, but is not very efficient for larger numbers as it only improved with the square root.As some units may be quite noisy, one may have check those, as a bad unit can increase the average noise quite a bit. Ideally one would used different resistors for averaging, depending on the individual noise levels.For the drift things are even worse, as same type chips tend to have a preferred drift direction.Here it may help to check multiple references to check of there are a few that are really off the pack.In this case it can help to have different types of references, not all the same.Temperature drift may be a little better than aging, but there still tends to be a more or less common square and higher part. So only the linear part may get some compensation - the higher order effects tend to be correlated. Chances are chips from the same batch could behave similar - so the average may not be much better than a typical one and a selected unit may very well be better.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 26, 2020, 08:28:03 pm
content: Quote from: Kleinstein on February 26, 2020, 07:48:26 pmThat makes sense... In that case it would almost make more sense to buy a bunch and test them all to hand pick a "best" one to use so it's just like selecting the best LTZ to keep/use.B

author: Kleinstein
author_rank: Super Contributor
timestamp: February 26, 2020, 09:08:05 pm
content: Temperature drift is only one aspect. There are also noise and the long term drift that can matter.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: February 27, 2020, 03:27:50 pm
content: I have found many pitfalls trying to series/parallel ref102c references as you are trying. The biggest and first issue is burn in time, after you have over 100 hours on multiple references only then should you start cherry picking form the selection you have. From my experiments I started off by trimming each of mine during burn in and found that some required very minimal trim while others required more than expected. Depending on if you plan on trimming your own refs I would suggest getting initial vout without trim with logging humidity,temp, input voltage, and output voltage daily and after 100 or so hours pick the best untrimmed refs to stack.

author: iMo
author_rank: Super Contributor
timestamp: February 27, 2020, 04:32:54 pm
content: The REF50xx is a bandgap based (1.23V up) reference, the REF102 is buried zener based (6.9V). Thus it could be the stacking 5010 via shorting Vin and Vout may work fine (while feeding the chip with a constant current) as described in the first post.

author: notfaded1
author_rank: Frequent Contributor
timestamp: February 28, 2020, 04:34:14 am
content: Quote from: imo on February 27, 2020, 04:32:54 pmThey worked in series in posted link... very low drift and in series they made 1000V then megavolt outputs with low drift. That's what made me think the same thing could work in parallel to reduce the drift issues. Same idea different arrangement. It made me picture a solution for another low drift 10V reference.As @Kleinstein said... what about the noise though? There may be only one way to find out for sure. One advantage to the REF5010 is it's already a precision 10V reference. There aren't any resistors needed to step up the voltage to 10V which would be affected by temp and aging too.Bill

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2020, 01:37:42 pm
content: The ref5010 is already a 10 V reference - this has some advantage for low demand on the stability, but it is also a problem as it limits the stability. Averaging help against random noise, but not mauch against aging. So one saves the resistors for the 7 to 10 V scaling, but one is stuck with the given quality grade inside the chip. With plastic case the stability is also not very good.The more logical part for sich a stacked high voltage reference would be more like a raw 7 V reference in a hermetic case, so more like LM129 (obsolete), LM399 or LT1021-7 and maybe selected 1N829. With so many references in series scaling the final result and using something like 1.4 times the number is not a big deal.Parallel connection to get lower noise needs quite a large number - so it may be better to start with a higher grade and do less averaging.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 03, 2020, 11:25:05 am
content: Multi zener in parallel.

author: PixieDust
author_rank: Frequent Contributor
timestamp: November 10, 2022, 05:16:18 am
content: Quote from: Kleinstein on March 01, 2020, 01:37:42 pmThese are very expensive if they don't have good stability due to their case.