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I got an infrared led emitter, with model ""L1I0-0850060000000" and the datasheet is plenty of technical data but I can`t find why it has three terminals - 2 anodes and 1 catode. Usually it's used for data transmittion.

Datasheet: https://www.lumileds.com/uploads/685/DS191-pdf

Here is the datasheet showing the three terminals:

enter image description here

I don't have many experience with light data links, but I know that some common leds have three terminals to allow switching the color. As far as I understand, this model is made for one specific infrared radiation - I could be wrong.

Has someone any idea on how to figure out this? I tried looking on google but cound't find a solid answer. I plan to use this for digital transmission.

Ramiro Vargas
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    There are only two conductors visible in the top view. I suspect that the centre tab is for heatsinking but that there is a limit on the pad size for mechanical reasons. Would this be to avoid a reflow soldering issue? – Transistor Feb 24 '19 at 18:15
  • the datasheet states that the part number `L1I0-0850060000000` is `peak wavelength of 850nm and a FWHM beam angle of 60°` ...... the reason for the two LEDs could be either luminous intensity or beam pattern ...... if you have one of those LEDs, then you could check how the beam pattern is different from one side to the other ..... shine the light on a piece of paper and view the pattern with your phone camera ..... afterthought: i don't know much about fiberoptics ..... i wonder if the light from the two LEDs would exit a fiber strand at different angles and therefore separate – jsotola Feb 24 '19 at 18:29
  • Your question SEEMED to be asking whether the two Anodes were functionally different. You mention some LEDs producing more than one wavelength of light. However, you have accepted an answer that does not address this question at all and which simply states that the centre pad is a thermal sink point (which it is). I'm puzzled as to why you consider that that is a good answer to what you are asking. – Russell McMahon Feb 26 '19 at 12:03

3 Answers3

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It's indeed as @Transistor suggests. The centre tab is a thermal pad. Check this Assembly and Handling Guidelines , page 3

Huisman
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  • See my answer. That is the norm but not wholly the case in this case, probably :-). – Russell McMahon Feb 25 '19 at 02:29
  • If you'd look carefully at the Guidelines i linked to, it says **"Thermal pad – Anode"**. So, it is fully the case. It's a thermal pad (and anode as well, but that was already clear from the datasheet). – Huisman Feb 26 '19 at 07:48
  • The question "seems" to be (non verbatim) "Why are there two "Anodes" and are they different". If looking closely at page 3 of a data sheet revealed useful relevant information then adding the reference and information to your answer would seem wise. And still does. I suggest that you add it. The centre tab is a thermal tab. The centre tab is an Anode that is electrically identical to the other anode. – Russell McMahon Feb 26 '19 at 11:59
  • You cannot "accept" all answers. You CAN upvote as many as you wish that you consider useful. Note that the criteria shown when you hover over the upvote arrow is "This answer is useful". If you value answers you should (probably) upvote them to encourage the people who spent time trying to help you. [The "rep" makes no difference to me either way - to some people it may]. – Russell McMahon Feb 26 '19 at 13:04
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In a number of Lumiled devices the middle conductor is neither Anode nor Cathode and is used for thermal sinking of the die.

In thus case the central conductor is shown in the datasheet as "Anode" as is one of the side pads.
While this COULD be a datasheet typo, Lumileds usually provide good quality datasheets and it is likely that both pads are electrically connected, as shown. The use of 3 pads is most likely related to this allowing a standardised Luileds pad specification for manufacturing.

enter image description here

The pads are NOT labelled Anode1 Anode2 or similar - there is no indication that they are different electrically.

The lead frame image suggests that the areas concerned are electrically common. This is not certain but likely.

There is no good reason to doubt the datasheet, and a check may be made with a suitably low voltage Ohm-meter without likely damage.
No Vreverse is specified, and a footnote states that the LEDs are not designed to be driven in reverse bias. However, the circled device shown below is not mentioned in the datasheet but is probably a diode or zener or (functionally) both. A diode is often used in this location to prevent Vreverse damage.
A zener or similar here protects against ESD damage in reverse breakdown mode and against Vreverse damage in fwd conduction mode.

enter image description here

Russell McMahon
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  • I havent the leds with me right now to check the continuity between both "anodes". But the EAGLE footprint for this component has three terminals: A_1, A_2 and K. I thought A_1 stands for "anode 1" and A_2 for "anode 2". – Ramiro Vargas Feb 25 '19 at 02:39
  • @RamiroVargas Eagle is obliged to have two names in the event that you wish to treat them differently for whatever reason. That **MAY** have bearing on what Lumileds do, or may not. Based on "their getting things correct more often than not" I'll go with my answer. I **may** be wrong. So may they :-).| A eter will tell you - and I'd be interested in the result. A simple and (probably) no damaging test would be to do a supply+-Anodex-cathode-resistor-supply- test using Anode1 and Andode2 in turn for Anodex. If (as I'd expect) Philips and I were correct then the results would be identical. – Russell McMahon Feb 25 '19 at 03:25
  • Ok. I will do your suggestion and will post what I get. Thanks – Ramiro Vargas Feb 25 '19 at 04:20
  • My friend tested one led and he says there is continuity between both anodes. So I guess that just one of them must be connected to current supply. The other could be connected to a pad in the PCB just for the sake of having somewhere to drop heat. Right? – Ramiro Vargas Feb 25 '19 at 05:27
  • @RamiroVargas Presumably that merits an upvote to my answer - I don't need the 'rep' BUT it serves as a guide to others re the answer quality. The centre terminal is usually the thermal sink point. The package has Tjc = 2.5 C/W so for say 1A x 3.2V = 3.3 Watt in and about 1.2 Watt of light out that gives about 5 or 6 C rise AT THE CENTRE POINT. If yuou want the temperature to be stable you need to heatsink the centre connection reasonably well. ... – Russell McMahon Feb 25 '19 at 08:33
  • @RamiroVargas ... As temperature increases: efficiency falls, emission wavelength changes, ... . Changes are not vast if external sink is under about say 5 C/W. OK ish at 10 C/W. Worse as heatsink gets worse. – Russell McMahon Feb 25 '19 at 08:33
  • I created a PCB board to test. I included a random size area for the thermal sink – Ramiro Vargas Feb 26 '19 at 07:22
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The reason being, for this type of specialized LED, manufacturers often use the same package for many types of LEDs to simplify the production, same machines, same process, etc...

They also use the same package for sometimes multi chip LED. You have to pay attention as sometimes for LEDs within the same series same manufacturer and same package the connection may vary with sometimes the central tab connected to the anode, sometimes the cathode or sometimes not connected at all. I ran in trouble once because of this.

The central tab is also used a heatsink as the other answer mentioned.

Damien
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