Datasheets and pin ordering

heres the two sheets I'm talking about:

http://www.ortodoxism.ro/datasheets/stmicroelectronics/2168.pdf

These look ok

And this one looks the best(least ambiguous)

http://www.ortodoxism.ro/datasheets/motorola/MC7809.pdf

Is there any place I can get good datasheets instead of relying on luck to get the pins right? Whats the reason for this crap? Laziness, stupidity, or they really want you to screw up some components to get it right so they can make more money?

The motorola doc is the only one that seems like its any good. It seems the graphic design engineers don't realize that pin order is important?

Jon

A trip to the optician would seem in order, or maybe your monitor is no good, or your just plain careless. Just as well its just a cheap regulator.

I really don't see your issue - what regulator are you using?

For instance, this is a standard datasheet from On Semi (nee Motorola SPS)

It's perfectly clear for physical pin order. Perhaps you are confusing schematic pin order and physical pin order.

The two need have no relationship to each other except the function of a pin number is the same.

Standard regulator datasheet schematics usually show input on the left, adjust or gnd in the centre and output on the right. If the pins assigned happen to be (as with the LM317T) Input = 3, Adj = 1, Output = 2, then the schematic would show (left to right) 3,1,2 although the physical graphic shows clearly the pin numbering and positions.

Cheers

PeteS

? I have the two data sheets?

yes, and its perfectly obvious what the pin order is... is it perfectly obvious to you what the pin order is on the two data sheets I've shown?

yes, but at the time I was wiring up the regulator I didn't expect the pin order to be randomly determined...

Maybe there is a reason why you would order the pins(which is what you are doing when you label them) out of order but I don't see it.

Sure its my fault for not noticing that it was 1 *3* 2 But seems kinda stupid to me why you would do something like that when there is no need. I suppose it came after the fact though when they drew the graphic and probably had to have it match up with the schematic that was lableled that way.

Thats not the real issue... its just strange to me that it would be done like that for no reason that I can see as it just makes it less intuitive. It would be like when counting a group of 10 objects to start 8, 3, 5, 2, 9,

The main thing that gets me, which both you and bozo fail to see is that

http://www.ortodoxism.ro/datasheets/auk/S78LXX.pdf

On Page one in the OUtline Dimensions box

orders the pins 1,2,3 like one expects but that it does it using a 2D perspective from the "top" or "bottom"... this is completely ambigously as the top looks exactly like the bottom except for the pins. Its entirely possible that they mean the bottom since it shows the pins and if it were the top they would not show then... but this is somewhat ambigous to someone what does know what the bottom or top is(as if you get it wrong you flip the pin order from 1,2,3 to 3,2,1 and obviously you'll screw something up).

It could be me though... my issue is specifically with that pdf S78LXX and not with the ones you have given as it is obvious. Maybe its clear to you but if so then why. I'm not asking what the real pin order is for the part but how to determine the pin order given that specific datasheet(a big difference). If you can do it unambiguously then there is probably something I'm missing... if you can't then theres a problem with that datasheet(atleast probably).

Jon

hmm... maybe you would be right but since you don't seem to offer any reason to why I am wrong makes me think that you are just BS'ing.

If you are going to say something like that then tell me why, on the 2 sheets I gave, where it tells you the pin order unambiguously else I have to believe you

http://www.ortodoxism.ro/datasheets/auk/S78LXX.pdf

First page under Outline Dimensions...

given that datasheet determine the pin order unambiguously. If you can't then maybe there is something wrong with your eyes? If you assume the graphic i the lower left corner is looking at the bottom then I feel that is a big assumption(atleast for someone that is not used to looking at these types of graphics).

Maybe there is some standard think similar to how DIP's have the little circle or cutout in the corner to determine the first pin but I don't see that here.

Anyways... like I said.. if you are going to say that s*it then back it up with some factual evidence instead of just trying to say something personal else I gotta take your argument as crap.

(and use the damn datasheet for the S78LXX that I gave and not some other one where its obvious. My problem is not with determing the pin order but with determing the pin order from that specific datasheet.).

I eagerly wait your response, Jon

oh, nevermind... sorry... didn't know you were from aol.

someone

the

I agree with you that datasheets do not always show clear pin-outs, escpecially with discrete devices, but in your http://www.ortodoxism.ro/datasheets/auk/S78LXX.pdf case I think it is quite clear. As you say yourself, since they show the pins you should look at the side where the pins are. What is top or bottom is completely irrelevant. And in this case, since they don't even mention top or bottom, they do not create any confusion, so it is actually a very clear datasheet.

--DF

huh?

If you look from the bottom and read the pins from left to right then you have, for example, In Gnd Out but if you read from the top then you have Out Gnd In(reading from left to right again).

If you write the word Apple on a transparent piece of papper then it does matter which side you read from... One side makes perfect sense and the other doesn't.

The hole point rests on if the pins shown are on the bottom or top. If it is a "solid" in that they don't show the the outline(which is says outline dimensions) then ofcourse thats the bottom...

but if "faces" are transparent then you can't tell what is bottom or top by that graphic. Now it maybe obvious that all faces are considered non-transparent but I didn't know this. I'm sure that datasheets are not written geared towards the amateur so that could be my problem... but simply showing an isometrix perspective solves that problem(which some data sheets seem to do and its completely obvious what is what(I suppose in some cases it could be confusing if the packaging is completely symmetric).

Anyways, I just feel they could have done a little better job. Now that I know the pins are shown cause its *suppose* to represent the bottom then its not a big deal. It just seems kinda stupid that looking at it one has to(if they are not familiar with the "rules") have to "guess"(i.e., assume something that might not be true). There are ways to be completely unambiguous and thats by including an isometric perspective. I guess I shoudln't bitch though. (not that I'm really bitching but just trying to find out whats going on and to make sure.)

Actually I took a course in graphic engineering many years ago so I should probably not have had any problem. Although I do remember using dashed lines for elements that were "behind".

Anyways,

Thanks, Jon

that

entirely

were

flip

Out

is

by

simply

sheets

its

to(if

From a mechanical point of view these drawings are completely clear. They show the device from all its important sides by simply rotating it. There is no reason whatsoever to assume that the device is transparent, especially since no mention is made of top or bottom or whatever.

--DF

Hi, Jon. Sorry, but Ich Bin Ein AOLer, too. Teenage daughters, you know. They'd just die without AOL. :-(

A couple of things come to mind here. First, the two data sheets you're talking about _do_ happen to be perfectly correct, even if the first isn't as clear as possible.

The first says "BOTTOM VIEW" in caps right next to the drawing of the part. It's customary when only giving one view on a drawing to specify the view, which they have done. The business of "1, 3, 2" is a bit of a "gotcha", and it's definitely not as clear as, say, the National Semiconductor datasheet:

where they actually have arrows going from pin descriptions to pins on the bottom view.

The second S78LXX data sheet is perfect. They give the standard three regular views, number the pins on the bottom view, and give the pin numbers on the functional schematic. I would suppose you might not be too familiar with technical drawing. That's not really critical, but you might want to just wander through a high school technical drawing book when you get a chance, and get up to speed. The pinout is just bass-ackwards from the TO-220 pinout you're familiar with.

Look. I've smoked both the TO-92 78LXX (plugged it in backwards) as well as an LM317CT (circuit layout IN-ADJ-OUT-BOOM). When I did that with the LM317, though, they were going for about 10 times as much in today's dollars.

The problem with the drawings is that they aren't what you expect. That can be a problem with datasheets. Very rarely, you'll find an error. Sometimes, you'll find something that isn't very clear. That's more common.

But you need some perspective here. You're a hobbyist, trying to get up to speed on some pretty basic stuff. The semiconductor manufacturers do know what they're doing. If they didn't, they'd be out of business.

Even as a technician or engineer, the rule of thumb is to look for your mistake first -- almost always, you'll save a lot of time that way. And you really have to look at each datasheet as an opportunity to learn. Clear your mind, get a cup of coffee if it helps, and take the time to really read and understand the information there. It will be well worth the time. Then, if something isn't clear, see if the part is second-sourced, and try to get another datasheet. If it's single source, send an email to the app engineers at the manufacturer. They do have people who are paid to help. Just neglect to mention that it's a hobbyist one-off, and make sure to read the datasheet first to avoid looking foolish.

If it helps, I've found there's a slight correlation between the length of a .pdf file and the clarity of the datasheet (not including those which have been scanned). And I find National Semiconductor datasheets are generally (not always) put together with more care than most. Either that, or I'm more accustomed to their way of describing things. But I'll look there first if I can.

What I'd like to know, though, is what you're doing playing with TO-92 packages with your power supply, anyway. They're small, their thermal resistance is around 160 to 180 degrees C per watt, and they aren't really made for attaching a good heat sink. You're cranking current, and you're going to need TO-220 or TO-3 packages here.

Let's assume your 25.2VCT transformer has an unregulated 34V, and you're using your LM317 to put out 3.3V at .5A that means your power dissipation will be

(34V - 3.3V) * .5A = 15.35 watts [Note: Power in a pass element = volts dropped * amps passed]

Your little TO-92 package will glow like a nite lite. Isn't going to happen.

If I could offer you a little free advice. Go to Surplus Sales of Nebraska

and take a look at their Triple Deltron Power Supply (PS) 10656X, that has two 12 - 16 vdc outputs @ 2.5 amps each and a 5 vdc output @ 8 amps. It costs $35 in single quantities. The two 12 - 16 vdc supplies are adjustable, and all the power supplies have independent current limit adjusts on board. If you mount this supply under your bench, you can be set up with a mongo +5V and a +/-12V supply (as well as a 24V supply for the industrial stuff, if you go from the +12 to the -12), which should get you 80% of the way toward where you want to go. Just use a 5 amp 3AG fuse (not slo-blo) in series, and mount that with an industrial power switch in a jiffy box.

If you're dying for a variable supply too, get a 28VDC @ 1A linear open frame ((PS) IHB28-1) for $25, set the on-board current limit for 1/2A, and place an LM317CK in series to give you your 1.25V-to-24VDC variable supply. Don't forget to put 10uF caps at the input and output of the regulator. And also, get a good heat sink capable of dissipating more than 15 watts without cooking the LM317CK IC.

Linear open frames are typically based on a standard LM723 circuit (not shown in datasheets -- from what I understand, someone tried to copyright the circuit a long time ago, without success). They have very low ripple, great line and load regulation, and they're pretty much indestructible, as long as you keep them fairly cool. It might also be a good idea to run a couple of small muffin fans on the open frame linears to help with heat dissipation. They also have remote sensing, which means they can compensate for line drops to the load.

If you want, you can also put 0.1 ohm 1% resistors in line with each V+out, if you put the V+sense on the other side of the resistor. You can then use your DMM and a 4PDT break-before-make switch to read current exactly with an autoranging DMM on whichever supply you choose (100mV/amp, to the resolution of the meter you're using).

You'll have the electronics for the whole shebang for less than $75. That way, you can spend your electronics time actually learning, instead of preparing to learn. A good bench power supply is a necessity for electronics, so you might as well just get something good on the bench right now, and play when you have the toy. You're walking into getting stuck in a chicken and egg problem.

Good luck Chris

Heh, its obvious to you ;) Its not 100% obvious to me and leaves something like 3% ambiguity(being resonable)... while, say, the isometric view leaves

Although you cannot be at 0% since on another datasheet they did label the view as bottom. If it was not ambiguous to the person who wrote that they would not have done it. Obviously they must have thought to themselfs(even if for a nanosecond) that they should write it(hence there was some ambiguity). That or they could have just did it for fun. What if they wrote top instead? Would there still be no confusion?

My point is that it might make complete sense to you but thats simply because you probably have more experience dealing with them... take some avg joe's and ask them and I'm sure you won't get 100% positive results. This leads me to the conlusion that they should show the isometric view as virtually unambiguous. Maybe there are overiding reasons not to do this but thats a different story. I was mainly interested in how to interpret it and since I don't really doubt you I will assume you are right(obviously you are since I didn't destroy my regulator(which I actually tested before I posted anyways)). Just trying to be absolutely clear on whats going on so if I get another datasheet and it does the same thing I can be confident that I won't screw up my component.

Jon

orders

as 1,

data

"bottom"

leads

guess

the

regulator(unless I

voltage

for

I looked at your datasheets and I do agree that the 132 numbering thing is a bit odd, but there is nothing unclear about the pictures. Standard drafting (or is it draughting) technique is to draw non-hidden features with solid lines and hidden features with dashed/broken lines. Since the leads don't protrude thru the top of the part, it should now be clear to you that the bottom was pictured. The bottom is the side that would normally be placed against a circuit board. The top would be the portion that would normally be visible when the part is mounted to a board.

or

Well, I'm in complete agreement. You've the benefit of looking with fresh eyes and can see the laziness and crass stupidity that turns up too often in these things. All they really need is a labelled perspective drawing but that'd then be regarded as non-technical, hence passe. john

well its obvious now but it wasn't obvious at 3AM ;) The datasheet should take those types of considerations into account. Specially the 1 3 2. I swear I first saw 1 2 3.

Thanks, Jon

I'm glad someone agree's with me ;) Its not that Theres anything technically wrong with what they did but seems that they could make it alittle easier on some of us. Its good to see some of these datasheets using the perspective view so it's very easy to get it at a glance so one can get on with the real work(instead of trying to make sure the the pin ordering is correct).

Thanks, Jon

It is unambiguous. Each drawing is rotated 90 degrees. The vertical diagram, when rotated 90 degrees to the horizontal, must end up with its flat side down, or its flat side up. Picture it: to rotate from the vertical position shown to horizontal, how could it end up with the pins facing away from you *and* lying on its round side as shown? Impossible with only a 90 degree rotation.

Logically, if you don't know about engineering drawing, how could you see the pins if they were facing away from you?

I suppose it's something like a doctor reading an xray: he or she would see things on it that are obvious that I would miss. Or, if someone posted the engineering drawing of a nuclear submarine or a pocket watch or whatever, you wouldn't be able to read it unless you were trained/experienced in that field.

Ed

If you can't

Oh hell - talk to us after you've correctly identified the pin 1 end of an IC, and correctly identified where it goes on the board, and then plugged it in backwards. Three times in a row.

Ed