Advantages of Cells in DIL Package - Page 1
Forum section: electronics / projects

author: SparkFly
author_rank: Regular Contributor
timestamp: January 22, 2017, 03:55:44 pm
content: Hi all,I have been reading some pages on HP oscilloscope repairs, and noticed that a few issues are the result of a dead cell inside NVSRAM packages. Aside from the advantage of not needing to solder a separate cell (and maybe some voltage sensing circuitry) elsewhere on your board, what other advantages (if any) are there in using such a device? Whilst the devices I have looked at claim to have a minimum of 10 years data retention, and 10 years is a relatively long time for electronics, wouldn't the pain of a dead cell require a pretty compelling reason to use such a device?Of course, I might be assuming that not needing to use a separate cell/associated circuitry isn't a compelling enough reason... I'd still be interested to hear if anyone else knows of other benefits of including the cell inside the DIP vs a little extra circuitry.Many thanks for your time.SF

author: Ian.M
author_rank: Super Contributor
timestamp: January 22, 2017, 04:38:44 pm
content: Leakage - the cell is epoxy potted so when it fails it wont destroy the instrument.Removable without loss of contents.Otherwise its a crass decision, especially if not socketed.

author: SeanB
author_rank: Super Contributor
timestamp: January 22, 2017, 04:52:12 pm
content: Well, first of all no need to clean the board after assembly, no need to have special handling to avoid shorting a battery, no need to have extra covers to prevent shorting in use from dust, and most importantly it survives the warranty period, is a single part to install and means no special processing at all during manufacture, service or field servicing , plus no special spares handling as well.That it will fail after 10-20 years is not a worry, you will be buying a new one, or buying service instead. As IanM says being potted means no leakage, or at least the leakage is confined to inside the sealed package, plus those cells inside rarely leak till at least 30 years after manufacture.

author: Benta
author_rank: Super Contributor
timestamp: January 22, 2017, 05:58:40 pm
content: Advantages? Today, none. This kind of device is a child of its time, and even illegal to sell today in certain regions of the world, EU being one. If you check the manufacturer websites, you'll see that they have mostly disappeared.Replace it with a Cypress/Ramtron NvRAM and you're done.

author: Ian.M
author_rank: Super Contributor
timestamp: January 22, 2017, 06:10:05 pm
content: There's still the need for battery backed RTC chips, and FRAM's destructive read requires extra circuitry to prevent power glitches destroying data.. Maybe there's an opportunity to make pin-compatible replacements as a potted module with an exposed CR1632 holder?

author: Benta
author_rank: Super Contributor
timestamp: January 22, 2017, 06:33:31 pm
content: Quote from: Ian.M on January 22, 2017, 06:10:05 pmMy apologies, I meant nvSRAM from Cypress/SimtekConcerning the "piggy-back" clip-on battery solution, ST tried this to get around the EU battery directive. It was commercially a total flop.To solve the RTC issue, the only viable solution at this point is a PCB-mounted battery clip.

author: SparkFly
author_rank: Regular Contributor
timestamp: January 22, 2017, 07:33:17 pm
content: Thanks all for your answers, they do make a lot of sense.Benta, may I ask which directive you are referencing? I have tried looking, but there seem to be a number of EU battery directives.Many thanks,SF

author: Benta
author_rank: Super Contributor
timestamp: January 22, 2017, 07:53:24 pm
content: QuoteIt's called the "Batteries Directive", DIRECTIVE 2006/66/ECThere's a lot of stuff in it, prohibiting Cadmium and Mercury cells, for instance.Relevant for us electronic guys is the part mandating that batteries must be disposed of separately. This means: no soldered-in batteries on PCBs (clip needed instead) and no embedded batteries like in the NVRAM we're discussing.I've no idea how Apple got around this one with their non-repairable iPhone. Hammer, perhaps, when disposing?

author: DBecker
author_rank: Frequent Contributor
timestamp: January 22, 2017, 08:23:57 pm
content: There is an additional advantage: leakage current.An external cell is likely to have higher leakage current, even if the assembly is carefully cleaned and sealed.A replaceable cell has contacts exposed to contamination. Pollution will increase the leakage over time.The worst effect is fingerprints. While the factory installed battery might last five years, the replacements could last only 6 months to a year because contamination bridges the battery surfaces.I still prefer batteries that are easily replaceable for my own equipment. But as a friend used to remind me, "you are not a market".

author: Benta
author_rank: Super Contributor
timestamp: January 22, 2017, 08:28:34 pm
content: QuoteI think that was in post #2 already...

author: SparkFly
author_rank: Regular Contributor
timestamp: January 22, 2017, 08:52:50 pm
content: Thanks again Benta, I shall give that a read.