[solved] D-flip-flops (TTL) driving me crazy (going haywire instead of 1 or 0) - Page 1
Forum section: electronics / projects

author: omulki
author_rank: Unknown
timestamp: August 12, 2017, 12:19:29 am
content: Hi there.This posting might turn out to be really embarrasing, but I'm stuck with something, that could be very simple for most of you:I'm using a 74LS189, which is more or less a bunch of D-flip-flops with some logic at both ends.http://ltodi.est.ips.pt/lab-dee-et/datasheets/TTL/74189.pdfMy problem: as soon as I try to set the chip to read or write, it gets hot and does nothing, that I would expect. Best case: All outputs go crazy. I've tried binding all inputs to zero (A-inputs as well as D-inputs). No matter what, as soon as I set "chipselect" or "writeEnable", it gets hot and does nothing sensible.Of course, I checked the supply rails for ringing and such. Nothing to tell as far as my old CRO goes. I've tried several different power supplies and I think that I've hooked up any capacitor one could suggest. Supply is 5.0 V, steady as a brick, DC to 1 MHz.The datasheet speaks of 37..55 mA typical operating current, which seems a real lot to me, but anyways, the chip getting hotter, than bearable to touch indicates a much higher power consumption. (Haven't measured that, estimating 200 mA).Does anyone have any suggestions?TNX.OM.

author: C
author_rank: Super Contributor
timestamp: August 12, 2017, 12:50:54 am
content: couple of thoughtsVoltmeter check of power supply 4.5v to 5.5vdo not ground unused pins, Use a pull up resistor to VccDisconnect output pins , High load can cause heat.You might be powering the chip with other pins then with 8 for ground and 16 for Vcc

author: Rerouter
author_rank: Super Contributor
timestamp: August 12, 2017, 12:52:00 am
content: First up, 5v * 37mA = 0.2W more or less, so you should not feel it get hot, perhaps a little warmer than ambient, but i would not expect hot.Now instead of hard tying your pins to ground, instead try a pullup of say 10K to VCC, based on the datasheet, its lowest power state is with all inputs pulled up. with all at ground, it would be supplying a fair amount of extra current,You say your 5V is steady. good, but your certain you dont have an odd by 1 error, (e.g. correct pin, looked over with fresh eyes.)If that is all good, what current is it pulling on the 5V rail? if its more than 100mA, you may have a toasted chip.If any of your outputs are shorted to ground, it appears it can sink atleast 150mA into that pin, so pull out a multimeter and make sure nothign is shorted.

author: rstofer
author_rank: Super Contributor
timestamp: August 12, 2017, 12:54:19 am
content: If it were mine, I would bet there is a shorted output. The chip shouldn't get hot!All inputs need to be valid level '1' or valid level '0'. Floating inputs can sometimes lead to excessive current.I would pull all the A and D lines to '0' or '1' (probably '1' through a 1k resistor), leave the O lines open and pull the WE' and OE' lines to '1', again through a 1k resistor. Then measure the current.That's a pretty neat device. I hadn't run across it before.

author: omulki
author_rank: Unknown
timestamp: August 12, 2017, 09:05:42 am
content: First of all: thank you.Btw. I'm absolutely sure, that it is okay to tie all address and input pins hard to ground or VCC (w/o resistors). I've seen people doing that successfully. Also, I'm equally sure that it is okay to tie chipselect to ground. After all, its (foolproof) TTLs, not a micro. Problem persists with open outputs, but the only thing I had attached to them was an inverter (74LS04)... couple µA shouldn't be too much a load :-) Yes, I had the outputs of the 189 connected to INputs of the 04 :-)Double checked every connection (breadboard) with fresh eyes, next day, no beer. Even built a minimalistic test setup aside of my project.Go figure:As it turns out, my complete stock of 74LS189 is counterfeit rubbish. To an extent, that some of them don't even have all 16 pins. See photo; compare the labelling, its identical (including the date and fabric codes) on two chips with a differing pin number.I cannot (or shouldn't publicly) express the feelings I have for China.OM.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 12, 2017, 10:56:00 am
content: And how much money you was thinking to save with ordering in china ?Lesson learnd, next time you save money for big orders only from normal shops.I only buy LCD displays in china, together with stuff like a DIP converter, switches or pin headers, whatever dont run on power,i also bought 10UF ceramic capacitors, only i am not sure about the quality, next time i buy for €0,50 each, instead of 100 for 4 dollar,what was i thinking : connecting a 4 cent cap to a 5 euro chip ?I also have these rotary encoders from china, no problems so far, others might say i,m crazy,i look at it as stuff that needs replacement one day sooner or later, like the LCD displays.

author: omulki
author_rank: Unknown
timestamp: August 12, 2017, 11:06:03 am
content: Costs are no issue and I was surely not trying to save anything (c'mon, I'm bying 64 bits of RAM for the price of a gigabyte - doesn't make me feel cheap altogether :-). This (fairly antique) chip was simply sold out at every German store, so I resorted to some Chinese source. Lesson learned. I have now found a store in Austria where I got their very last pieces for 8 € each, plus some 74LS219 which are much cooler anyways, as they have non-inverted outputs. Hoping for a datecode of 8xxx, TI real deal.Have a nice day!

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 12, 2017, 11:11:26 am
content: Ordering at Mouser also ships from Germany, did you know ?

author: Ian.M
author_rank: Super Contributor
timestamp: August 12, 2017, 11:25:12 am
content: Don't hard-tie bipolar TTL inputs to Vcc (+5V) unless you are CERTAIN that the specific chips you are using don't use the classic TTL input circuit to the input transistor emitter.Seehttp://www.edn.com/electronics-blogs/living-analog/4428104/Pull-up-Resistors-for details.The 74189 is pretty much obsolete so very few reputable distributors stock it. Jameco and Futurlec claim to have stock and as you have found there are still a few to be had from some local specialists. Newer/faster versions (S, LS or F) are rare like hens teeth - most suppliers that still list them say out of stock or NLA and those that claim to have it I mostly wouldn't trust further than I could spit upwind.

author: omulki
author_rank: Unknown
timestamp: August 12, 2017, 11:34:02 am
content: Quote from: Ian.M on August 12, 2017, 11:25:12 amThank you. I wasn't aware of that.Gladly, all the TTLs I've been treating this way have input and output buffers, so I never fried one.

author: rstofer
author_rank: Super Contributor
timestamp: August 12, 2017, 02:39:35 pm
content: Jameco does say they are in stock and the price isn't unreasonable. Shipping might be...http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?search_type=jamecoall&catalogId=10001&freeText=74189&langId=-1&productId=49883I've been doing business with Jameco (off and on) for a very long time - they're very reputable!

author: omulki
author_rank: Unknown
timestamp: August 17, 2017, 10:01:56 am
content: Just a little follow up to close the case.Got the new parts today, plugged them in and guess what? Worx a treat.Label code: TI Germany 8547. The good stuff.Also, that Chinese vendor fully refunded me for the fake chips. Honorable, I guess. Or he simply needed a lever to have my rather distinct rating deleted.I'm starting to enjoy this day ;-)OM.