UC2577 failed in storage? - Page 1
Forum section: electronics / general

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 22, 2012, 11:33:59 pm
content: I was working on a UC2577 based boost converter and the first time I tried to power it on, it drew a lot of current. After debugging, I found that the chip was internally shorted. After checking my circuit for faults that might have caused the failure, I replaced the chip and same problem. Then I took out a third chip (last one I had) and measured it before I even used it, and it was also bad.How would three chips in a row go bad from storage? They were all stored in a piece of antistatic foam, so ESD seems unlikely. Moreover, other chips (including some CMOS logic chips) in the same piece of foam work fine.

author: notsob
author_rank: Frequent Contributor
timestamp: November 22, 2012, 11:42:46 pm
content: not likely a bad batch, more likely someone wearing nylon undies handled them before they were sent to you.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 23, 2012, 04:11:08 am
content: Quote from: notsob on November 22, 2012, 11:42:46 pmtechnically speaking... just by touching or wearing that material wont do much harm. the wearer need a significant amount of "rubbing" with the material before she can build a dangerous voltage that can penetrate antistatic.

author: notsob
author_rank: Frequent Contributor
timestamp: November 23, 2012, 06:22:17 am
content: I was just trying to add some humour to the possibility of incorrect handling of the devices upstream.I once worked for a company that moved from 'casual' component handling, to fully antistatic procedures, (floor mats, table mats, ankle straps, discharge points at every bench, anti static holding bins, you name it), obviously this was quite some time ago, their faulty on manufacture and 'dead' board returns during the first 6 months dropped by an astonishingly unbelievable amount.So yes antistatic procedure are very important, and depending where you source your parts, there could be problems introduced upstream.

author: SeanB
author_rank: Super Contributor
timestamp: November 23, 2012, 02:42:19 pm
content: Could also be a faulty batch, a fake one or a contaminated batch that failed with time.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: November 24, 2012, 12:17:08 pm
content: If you've measured a brand new part and found it to be short circuit, I would very much doubt that static could cause a low impedanceshort- if anything, quite the reverse (until you plugged a faulty part in to a current bearing circuit -thenit might fail to short).It does sound to me like you have manufacturer rejects or even fake parts. How do the markings look? Where did you buy them from ? When you say "short", between what pins and what impedance are you seeing? What is your circuit?I have used these devices myself in the past, and not had any "Dead on Arrival" or subsequent demise problems. They can be unstable if not decoupled as per the spec sheet, however.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 24, 2012, 02:40:54 pm
content: They were TI samples I ordered a few years ago for a self driving model race car. (First year class project.) They went unused because it turns out the control circuit was the bottleneck and boosting the voltage would not do any good.